April 2001 Paper II

1) Discuss the metabolism of tyrosine Name the biologically important compounds derived from

tyrosine What are the inborn errors of metabolism of this aminoacid (April 2001 feb 2005 feb

2012 nov 2001)

ANS Tyrosine is an aromatic aminoacid It is synthesized from phenylalanine It is both

glucogenic and ketogenic

Catabolism of tyrosine

Step1 tyrosine is transaminated by tyrosine transaminase using PLP and alpha keto glutarate to

form p-hydroxy phenyl pyruvate and glutamic acid

Step2 p-hydroxy phenyl pyruvate is converted to homogentisate by hydrolase It is a copper

containing enzyme Ascorbic acid is required for the reaction

Step3 homogentisate is converted to maleyl acetoacetate by a dioxygenase called

homogentisate oxidase

Step4 Maleyl acetoacetate is converted to its isomer fumaryl acetoacetate by isomerase using

Glutathione

Step5 fumaryl acetoacetate is cleaved into fumarate(glucogenic) and acetoacetate(ketogenic)

Fig tyrosine catabolism

Other products formed from tyrosine

1 Melanin

- Tyrosine is hydroxylated by tyrosinase to DOPA(dihydroxy phenyl alanine) It is a

monooxygenase containing copper

- Tyrosinase acts again on DOPA to form DOPAquinone

-decarboxylation and oxidation of DOPAquinone converts it to indole quinone

Indolequinone is polymerized to melanin

2 Catecholamines

- Tyrosine is first hydroxylated to DOPA by tyrosine hydrolase It requires tetrahydro

Biopterin

- DOPA is decarboxylated to form Dopamine by DOPA decarboxylase a PLP dependent

enzyme

- Dopamine is hydroxylated to Nor epinephrine by dopamine hydrolase

- Nor epinephrine is converted to epinephrine by methyl transferase requiring SAM

Fig formation of melanin

Fig Formation of catecolamines

2 Thyroid hormones- specific tyrosine molecules is iodinated to form mono Di Tri iodo

thyronines and thyroxine

3 Tyramine-tyrosine is decarboxylated to tyramine by intestinal bacteria which is one of the

reasons for food allergy

Inborn errors of tyrosine metabolism

1 Alkaptonuria

- Itrsquos an autosomal recessive condition affecting 1250000 births It is due to defect of

homogentisate oxidase

-homogentisate accumulates becomes benzoquinone acetate and forms alkaptone

bodies and deposits in bone causing ochronosis Also it deposits in intervertebral discs

cartilages of nose etc Urine turns black on standing FeCl3 test is positive Benedictrsquos test is

strongly positive since homogentisate is a reducing agent Otherwise itrsquos a harmless condition

2 Albinism

- it is due to deficiency of tyrosinase leading to melanin deficiency Patient will have

nystagmus photophobia Skin is hypo pigmented contains naevi melanomas Hair is also

white Iris may be grey or red

3 Hypertyrosinemias

- Tyrosinemia type I autosomal recessive condition affecting 151000 births it is due to

fumaryl acetoacetate hydrolase deficiency In the first 6 months of life cabbage like odor

hypoglycemia seen and itrsquos usually fatal Urine contains para hydroxyl phenyl pyruvate

hydroxyl phenyl lactate

- Tyrosinemia type II It is due to deficiency of tyrosine transaminase Mental

retardation palmar keratosis painful corneal lesions and photophobia seen

2) Write short notes on

a) Metabolic role of methionine(oct 2003 feb 2007 aug 2008 feb 2009)

ANS 1 Methionine converts to SAM

2 SAM donates methyl group to methyl acceptors by methyl transferases to form S-adenosyl

homocysteine (SAH)

3 SAH loses adenosine using adenosine homocysteinase to form homocysteine

4 Homocysteine forms methionine by homocysteine methyl transferase This step uses methyl

tetrahydrofolate which becomes THFA using B12

5 Homocysteine combines with serine to form Cystathionine using Cystathionine synthase and

Cystathionine is hydrolyzed to cysteine and homoserine by cystathioninase

Fig Catabolism of Methionine

Transmethylation reaction is acceptance of a methyl group from a donor like S-adenosyl

methionine (SAM) by a compound resulting in another compound

Transmethylation reaction requires SAM which is obtained by accepting adenosyl group from

ATP by methionine by methionine adenosyl transferase

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

Other products formed from tyrosine

1 Melanin

- Tyrosine is hydroxylated by tyrosinase to DOPA(dihydroxy phenyl alanine) It is a

monooxygenase containing copper

- Tyrosinase acts again on DOPA to form DOPAquinone

-decarboxylation and oxidation of DOPAquinone converts it to indole quinone

Indolequinone is polymerized to melanin

2 Catecholamines

- Tyrosine is first hydroxylated to DOPA by tyrosine hydrolase It requires tetrahydro

Biopterin

- DOPA is decarboxylated to form Dopamine by DOPA decarboxylase a PLP dependent

enzyme

- Dopamine is hydroxylated to Nor epinephrine by dopamine hydrolase

- Nor epinephrine is converted to epinephrine by methyl transferase requiring SAM

Fig formation of melanin

Fig Formation of catecolamines

2 Thyroid hormones- specific tyrosine molecules is iodinated to form mono Di Tri iodo

thyronines and thyroxine

3 Tyramine-tyrosine is decarboxylated to tyramine by intestinal bacteria which is one of the

reasons for food allergy

Inborn errors of tyrosine metabolism

1 Alkaptonuria

- Itrsquos an autosomal recessive condition affecting 1250000 births It is due to defect of

homogentisate oxidase

-homogentisate accumulates becomes benzoquinone acetate and forms alkaptone

bodies and deposits in bone causing ochronosis Also it deposits in intervertebral discs

cartilages of nose etc Urine turns black on standing FeCl3 test is positive Benedictrsquos test is

strongly positive since homogentisate is a reducing agent Otherwise itrsquos a harmless condition

2 Albinism

- it is due to deficiency of tyrosinase leading to melanin deficiency Patient will have

nystagmus photophobia Skin is hypo pigmented contains naevi melanomas Hair is also

white Iris may be grey or red

3 Hypertyrosinemias

- Tyrosinemia type I autosomal recessive condition affecting 151000 births it is due to

fumaryl acetoacetate hydrolase deficiency In the first 6 months of life cabbage like odor

hypoglycemia seen and itrsquos usually fatal Urine contains para hydroxyl phenyl pyruvate

hydroxyl phenyl lactate

- Tyrosinemia type II It is due to deficiency of tyrosine transaminase Mental

retardation palmar keratosis painful corneal lesions and photophobia seen

2) Write short notes on

a) Metabolic role of methionine(oct 2003 feb 2007 aug 2008 feb 2009)

ANS 1 Methionine converts to SAM

2 SAM donates methyl group to methyl acceptors by methyl transferases to form S-adenosyl

homocysteine (SAH)

3 SAH loses adenosine using adenosine homocysteinase to form homocysteine

4 Homocysteine forms methionine by homocysteine methyl transferase This step uses methyl

tetrahydrofolate which becomes THFA using B12

5 Homocysteine combines with serine to form Cystathionine using Cystathionine synthase and

Cystathionine is hydrolyzed to cysteine and homoserine by cystathioninase

Fig Catabolism of Methionine

Transmethylation reaction is acceptance of a methyl group from a donor like S-adenosyl

methionine (SAM) by a compound resulting in another compound

Transmethylation reaction requires SAM which is obtained by accepting adenosyl group from

ATP by methionine by methionine adenosyl transferase

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

Fig Formation of catecolamines

2 Thyroid hormones- specific tyrosine molecules is iodinated to form mono Di Tri iodo

thyronines and thyroxine

3 Tyramine-tyrosine is decarboxylated to tyramine by intestinal bacteria which is one of the

reasons for food allergy

Inborn errors of tyrosine metabolism

1 Alkaptonuria

- Itrsquos an autosomal recessive condition affecting 1250000 births It is due to defect of

homogentisate oxidase

-homogentisate accumulates becomes benzoquinone acetate and forms alkaptone

bodies and deposits in bone causing ochronosis Also it deposits in intervertebral discs

cartilages of nose etc Urine turns black on standing FeCl3 test is positive Benedictrsquos test is

strongly positive since homogentisate is a reducing agent Otherwise itrsquos a harmless condition

2 Albinism

- it is due to deficiency of tyrosinase leading to melanin deficiency Patient will have

nystagmus photophobia Skin is hypo pigmented contains naevi melanomas Hair is also

white Iris may be grey or red

3 Hypertyrosinemias

- Tyrosinemia type I autosomal recessive condition affecting 151000 births it is due to

fumaryl acetoacetate hydrolase deficiency In the first 6 months of life cabbage like odor

hypoglycemia seen and itrsquos usually fatal Urine contains para hydroxyl phenyl pyruvate

hydroxyl phenyl lactate

- Tyrosinemia type II It is due to deficiency of tyrosine transaminase Mental

retardation palmar keratosis painful corneal lesions and photophobia seen

2) Write short notes on

a) Metabolic role of methionine(oct 2003 feb 2007 aug 2008 feb 2009)

ANS 1 Methionine converts to SAM

2 SAM donates methyl group to methyl acceptors by methyl transferases to form S-adenosyl

homocysteine (SAH)

3 SAH loses adenosine using adenosine homocysteinase to form homocysteine

4 Homocysteine forms methionine by homocysteine methyl transferase This step uses methyl

tetrahydrofolate which becomes THFA using B12

5 Homocysteine combines with serine to form Cystathionine using Cystathionine synthase and

Cystathionine is hydrolyzed to cysteine and homoserine by cystathioninase

Fig Catabolism of Methionine

Transmethylation reaction is acceptance of a methyl group from a donor like S-adenosyl

methionine (SAM) by a compound resulting in another compound

Transmethylation reaction requires SAM which is obtained by accepting adenosyl group from

ATP by methionine by methionine adenosyl transferase

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

- it is due to deficiency of tyrosinase leading to melanin deficiency Patient will have

nystagmus photophobia Skin is hypo pigmented contains naevi melanomas Hair is also

white Iris may be grey or red

3 Hypertyrosinemias

- Tyrosinemia type I autosomal recessive condition affecting 151000 births it is due to

fumaryl acetoacetate hydrolase deficiency In the first 6 months of life cabbage like odor

hypoglycemia seen and itrsquos usually fatal Urine contains para hydroxyl phenyl pyruvate

hydroxyl phenyl lactate

- Tyrosinemia type II It is due to deficiency of tyrosine transaminase Mental

retardation palmar keratosis painful corneal lesions and photophobia seen

2) Write short notes on

a) Metabolic role of methionine(oct 2003 feb 2007 aug 2008 feb 2009)

ANS 1 Methionine converts to SAM

2 SAM donates methyl group to methyl acceptors by methyl transferases to form S-adenosyl

homocysteine (SAH)

3 SAH loses adenosine using adenosine homocysteinase to form homocysteine

4 Homocysteine forms methionine by homocysteine methyl transferase This step uses methyl

tetrahydrofolate which becomes THFA using B12

5 Homocysteine combines with serine to form Cystathionine using Cystathionine synthase and

Cystathionine is hydrolyzed to cysteine and homoserine by cystathioninase

Fig Catabolism of Methionine

Transmethylation reaction is acceptance of a methyl group from a donor like S-adenosyl

methionine (SAM) by a compound resulting in another compound

Transmethylation reaction requires SAM which is obtained by accepting adenosyl group from

ATP by methionine by methionine adenosyl transferase

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

2) Write short notes on

a) Metabolic role of methionine(oct 2003 feb 2007 aug 2008 feb 2009)

ANS 1 Methionine converts to SAM

2 SAM donates methyl group to methyl acceptors by methyl transferases to form S-adenosyl

homocysteine (SAH)

3 SAH loses adenosine using adenosine homocysteinase to form homocysteine

4 Homocysteine forms methionine by homocysteine methyl transferase This step uses methyl

tetrahydrofolate which becomes THFA using B12

5 Homocysteine combines with serine to form Cystathionine using Cystathionine synthase and

Cystathionine is hydrolyzed to cysteine and homoserine by cystathioninase

Fig Catabolism of Methionine

Transmethylation reaction is acceptance of a methyl group from a donor like S-adenosyl

methionine (SAM) by a compound resulting in another compound

Transmethylation reaction requires SAM which is obtained by accepting adenosyl group from

ATP by methionine by methionine adenosyl transferase

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

The transmethylation reactions are

Methyl acceptor Methylated product

Guanidoacetic acid Creatine

Serine Choline

Epinephrine Metanephrine

Nor epinephrine Epinephrine

tRNA Methylated tRNA

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

b) PCR (feb 2010 sep 2002)

ANS it is a vitro DNA amplification procedure in which millions of a particular

sequence of DNA can be produced within few hours

Two primers of about 20-30 nucleotides with complementary sequence of the

flanking region can be synthesized

I) DNA strands are separated by heating at 95c for 15 sec to 2 min

II) The primers are annealed by cooling to 50c the primer hybridise with their

complementary single stranded DNA produced

III) New DNA strand are synthesized by taq polymerase This enzyme is derived from

bacteria that found in hot springs The polymerase reaction is allowed to take place at

72c for 30 sec in presence of dNTPs

IV) Clinical applications

V) PCR detect even one bacillus present in the specimen Any other bacteria also

detect similarily This technique is widely used in the diagnosis of viral infections like

hepatitis C and HIV

VI) PCR allows the DNA in a single cell or in a hair follicle to be analysedthis is highly

useful in forensic medicine to identify the criminal

VII) PCR especially useful for prenatal diagnosis of inherited diseases

VIII) PCR is widely used to monitor residual abnormal cells present in treated patients

IX) Diagnosis of genetic disorder the PCR technology has been widely used to

amplify the gene segments that contain known mutations for diagnosis such as sickle

cell anemia etc

X) Real time PCR ndash quantitation of the number of virus present in the sample can be

calculated Eg viral load in HIV

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

Fig PCR

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

c) Metabolic acidosis(aug 2004 aug 2007 feb 2006 aug 2009 feb 2011)

ANS Acidosis is reduction of pH less than 738 it is classified into metabolic and

respiratory acidosis

Metabolic acidosis is primarily due to base deficit The bicarbonate deficit may occur

due to excess acid production or depletion of bicarbonate

Anion gap it is difference between measured cations and measured anions Usually it shows

the unmeasured anions The normal value is 12 mmolL

Metabolic acidosis is classified into

1 High anion gap metabolic acidosis- accumulation of acid

Renal failure- H+ excretion is less

DKA- ketoacid production is more

Lactic acidosis- hypoxia circulatory failure many drugs and bacterial metabolism

increases lactic acid

Methanol ethanol also causes lactic acidosis

2 Normal anion gap metabolic acidosis- both anions and cations lost but acidosis present

Diarrhea- loss of bicarbonate from intestinal secretions

Hyperchloremic metabolic acidosis- in renal tubular acidosis- which may be due to

either failure to secrete acid or conserve bicarbonate acetazolamide treatment

Compensation

Metabolic acidosis is compensated by hyperventilation so that pCO2 comes down

Features

PH will be low Bicarbonate will be low PCO2 starts decreasing due to respiratory compensation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

3) Write an account of DNA replication( aug 2007)

ANS DNA replication

During cell division two daughter cells receives DNA from mother cell The DNA divides

by the process called replication In daughter cell only one strand is from mother other is

newly synthesized This is called semiconsevative method of replication

Steps of replication

Each strand serves as template for new complementary strand synthesis The base

pairing rule is always followed

1 Initiation At the origin of replication (ori) there is an association of sequence-specific

dsDNA-binding proteins with a series of direct repeat DNA sequences This leads to the local

denaturation and unwinding of an adjacent A+T-rich region of DNA

2 Unwinding of DNA The interaction of proteins with ori defines the start site of replication

and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA

strand A critical step is provided by a DNA helicase that allows for processive unwinding of

DNA Single-stranded DNA-binding proteins (SSBs) stabilize this complex

3 Formation of replication fork A replication fork consists of four components that form in the

following sequence

(1) The DNA helicase unwinds a short segment of the parental duplex DNA

(2) A primase initiates synthesis of an RNA molecule that is essential for priming DNA

synthesis

(3) The DNA polymerase initiates nascent daughter strand synthesis and

(4) SSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA

The polymerase III holoenzyme binds to template DNA and synthesizes DNA in the 5prime to 3prime

direction Because the DNA strands are antiparallel the polymerase functions asymmetrically

On the leading (forward) strand the DNA is synthesized continuously On the lagging

(retrograde) strand the DNA is synthesized in short (1ndash5 kb) fragments the so-called Okazaki

fragments

4 Initiation and elongation The initiation of DNA synthesis requires priming by a short length

of RNA about 10ndash200 nucleotides long This priming process involves the nucleophilic attack by

the 3prime -hydroxyl group of the RNA primer on the α-phosphate of the first entering

deoxynucleoside triphosphate with the splitting off of pyrophosphate The 3rsquo-hydroxyl group of

the recently attached deoxyribonucleoside monophosphate is then free to carry out a

nucleophilic attack on the next entering deoxyribonucleoside triphosphate again at itrsquos α

phosphate moiety with the splitting off of pyrophosphate

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

5 Gap filling In mammals after many Okazaki fragments are generated the replication

complex begins to remove the RNA primers to fill in the gaps left by their removal with the

proper base paired deoxynucleotide and then to seal the fragments of newly synthesized DNA

by enzymes referred to as

DNA ligases

Fig DNA Replication

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

4) Write short notes on

a) Detoxification ( aug 2004 feb 2009)

ANS Xenobiotics are compounds which may be accidentally ingested or taken as drugs

or compounds produced in the body by bacterial metabolism

Various xenobiotics

Compounds accidentally ingested like preservatives food additives and adulterants

Drugs taken for therapeutic purposes

Endogenous compounds which has to be eliminated by body like bilirubin steroids

Compounds produced by bacterial metabolism

o Histidinehistamine

o Lysinecadaverine

o Ornithineputrescine

Phases of detoxification

1 Phase 1 reactions it is the alteration of foreign molecule by adding a functional group like

hydroxylation oxidation hydrolysis dealkylation Epoxidation etc the main function of phase

1 is to convert it into anon toxic metabolite

Eg Toluene Benzyl alcohol by oxidation

Benzene phenol by oxidation

Picric acid picramic acid by reduction

Aspirin acetic acid and salicylic acid by hydrolysis

Sometimes phase one reaction will to production of a toxic product

Eg Methanol formic acid

2 phase 2 reactions conjugation

A xenobiotic that undergone a phase 1 reaction is now a new metabolite that contains a

chemical group like OH NH2 COOH groups Phase 2 reactions lead to conjugation(addition) of

conjugating agents like

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

Glucuronic acid Bilirubin conjugated with glucuronic acid to form Bilirubin

Diglucuronide and excreted in bile

Sulfate conjugation phenol converted to phenol sulphate using PAPS(phosphor

adenosyl phosphor sulphate-active sulphate)

Cysteine and Glutathione alkyl or aryl halide epoxide are detoxified in this manner

Acetylation acetic acid s is conjugated to sulfanilamide INH

Glycine Benzoic acid is conjugated with glycine to form hippuric acid

Glutamine phenyl acetic acid is conjugated to form Phenyl acetyl glutamine

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

b) Oncogenes (nov 2001 feb 2007 aug 2008)

ANS Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src product

The c-Oncogenes are under the control of regulatory genes and are expressed only

when required

Activation of Oncogenes

Viruses chemical carcinogens chromosome translocations gamma rays spontaneous

mutations and all such factors may converge into one biochemical abnormality the

activation of Oncogenes which leads to malignancy

Examples for Oncogenes causing cancer

erb-B1- lung cancer

erb-B2-gastric tumors

erb-B3-breast cancer

sis- osteosarcoma by activating PDGF

abl- leukemia

Ras- leukemias lung cancer pancreatic and colon cancer Functions of Oncogenes

Oncogenes are normal genes whose products perform various functions in the cell

Products of many Oncogenes are polypeptide growth factors

Some of the products act as receptors for growth factors Eg Erb-B

Some oncogene products act on key intracellular pathways involved in growth control

Eg Src products

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

c) Role of kidneys in acid-bace balance(march 2002 oct 2003 feb 2005 feb 2007 feb 2009

aug 2010 aug 2011 feb 2012)

ANS Kidneys regulate acid base balance by

1 Excretion of H+ -In PCT cells CO2 combines with water to form carbonic acid using carbonic

anhydrase Then it becomes H+ and HCO3- This H+ is then excreted into lumen in exchange for

Na+

2 Reabsorption of HCO3- - sodium bicarbonate in the lumen becomes sodium and bicarbonate

Sodium is taken up by PCT cell in exchange of hydrogen ions H+ combines with HCO3- to form

carbonic acid which forms CO2 and water and both are reclaimed into the cell and converted

back to carbonic acid and again to H+ and HCO3- HCO3- is taken into blood with sodium

Fig Excretion of H+ fig Reabsorption of HCO3-

3 Excretion of titrable acid- The Na2 HPO4 becomes Na+ and NaHPO4 - Sodium is exchanged

with H+ ions and H+ combines with NaHPO4 ndash to become Na H2PO4 and gets excreted

Fig Excretion of titrable acid and ammonium ions

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

4 Excretion of NH4 + - Glutamine in DCT becomes glutamate and ammonia This ammonia is

secreted into the lumen which combines with hydrogen ions to become ammonium ions and

gets excreted

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

d) Gout (feb 2005 feb 2007 aug 2008 aug 2009)

ANS When uric acid levels increase in the blood it tends to get deposited as crystals in

synovial fluid of joints leading to inflammation and acute arthritis This disease is called Gout

Etiology

Primary gout

o 5-phosphoribosyl amidotransferase- there will be increased production of

purines due to absence of regulation on this enzyme Itrsquos a genetic defect

o Abnormal PRPP synthase- there will be increased production of PRPP due to

absence of regulation on PRPP synthase Itrsquos a genetic defect

o Salvage pathway enzyme deficiencies-there would be more availability of PRPP

leading to production of purines uric acid

o Von Gierkersquos Disease- due to G-6-Pas deficiency G-6-P is not converted to

glucose So it goes through HMP shunt resulting in more nucleotide bases

increasing urate production

Secondary Gout

o Increased production of uric acid- malignancy- lymphomas leukemias after

treatment of cancer cancer cells breakdown leading to hyperuricemia trauma-

tissue damage starvation-where catabolism is increased

o Reduced excretion- renal failure thiazide diuretics- which inhibits urate

secretion lactic acidosis and Ketoacidosis- interferes with urate secretion

Clinical features

Uric acid gets deposited in the cooler areas of body like distal joints to form tophi

Hypeuricemia leads to increased excretion of uric acid through the kidneys so uric acid crystals

gets deposited in the urinary tract leading to renal calculi

Treatment

1 Dietary Purine intake should be reduced alcohol should be restricted

2 Uricosuric drugs which increases the excretion of uric acid like probenecid should be used

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation

3 For calculi Allopurinol can be used It inhibits xanthine oxidase and reduces the formation of

uric acid Itrsquos a type of suicide inhibition like aspirin where the enzyme becomes completely

functionless

4 Colchicine an anti-inflammatory drug used in RA can be used to reduce inflammation in

joints

Lysch Nyhan syndrome

it is a X-linked inborn error of purine metabolism incidence 110000

deficiency of HGPRTase which acts in salvage pathway

so the salvage pathway is stopped and PRPP accumulates which will go for catabolism to

uric acid

Hyperuricemia leads to nephrolithiasis and gout

it is also characterized by self mutilation mental retardation