BioChem I - 05. Lipid.ppt

8/14/2019 BioChem I - 05. Lipid.ppt

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HEMISTRY OF LIPIDS

Definition:Lipids are organic compounds formed

mainly from alcohol and fatty acidscombined together by ester linkage.

CH 2R

Fatty alcoholOH C R

Fatty acidHO

O

+H2O

CH 2R O C R

O

Esterase (lipase) ester (lipid)


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Lipids are insoluble in water, but

soluble in fat or organic solvents(ether, chloroform, benzene,acetone).

Lipids include fats, oils, waxes andrelated compounds.They are widely distributed innature both in plants and inanimals.


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Biological Importance of Lipids :1. They are more palatable and storable to unlimited

amount compared to carbohydrates.2. They have a high-energy value (25% of body needs)

and they provide more energy per gram thancarbohydrates and proteins but carbohydrates arethe preferable source of energy.

3. Supply the essential fatty acids that cannot besynthesized by the body.4. Supply the body with fat-soluble vitamins (A, D, E

and K).5. They are important constituents of the nervous

system.6. Tissue fat is an essential constituent of cell

membrane and nervous system. It is mainlyphospholipids in nature that are not affected by

starvation.


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CL SSIFIC TION OF LIPIDS

1. Simple lipids (Fats & Waxes)2. Compound or conjugated lipids3. Derived Lipids4. Lipid-associating substances


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F TTY LCOHOLS

1-Glycerol:It is a trihydric alcohol (containing

three OH groups) and has the popularname glycerin.It is synthesized in the body from

glucose. It has the following properties:


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1. Colorless viscous oily liquid withsweet taste.

2. On heating with sulfuric acid orKHSO4 (dehydration) it gives acroleinthat has a bad odor. This reaction is

used for detection of free glycerol orany compound containing glycerol.

CH 2 OH

CH

CH 2 OH

HO

CHO

CH

CH 2

2 H 2 O

Heating, KHSO 4

Glycerol Acrolein


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3-It combines with three molecules of nitricacid to form trinitroglycerin (TNT) that is

used as explosive and vasodilator.4-On esterification with fatty acids it gives:Monoglyceride or monoacyl-glycerol : onefatty acid + glycerol.Diglyceride or diacyl-glycerol : two fattyacids + glycerol.Triglyceride or triacyl-glycerol : three fatty

acids + glycerol.5-It has a nutritive value by conversion into

glucose and enters in structure ofphospholipids .


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Uses of Glycerol :1. Glycerol enters in pharmaceutical and

cosmetic preparations.2. Reduces brain edema in cerebrovascular

disease.3. Nitroglycerin is used as vasodilator

especially for the coronary arteries, thus itis used in treatment of angina pectoris .Also, enters in explosives manufacturing.

4. Glycerol is used in treatment of glaucoma (increased intraocular pressure)due to itsability to dehydrate the tissue from itswater content.


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2-Sphingosine:

- It is the alcohol(monohydric) presentin sphingolipids.- It is synthesized in the body from

serine and palmitic acid.It is not positive with acrolein test .

CH CH NH 2

CH 2 OH

CHCH(CH 2 )12CH 3

OH

Sphingosine


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FATTY ACIDS

Definition :Fatty acids are aliphatic mono-carboxylicacids that are mostly obtained from thehydrolysis of natural fats and oils.

Have the general formula R-(CH 2)n -COOH and mostly have straight chain (a few exceptionshave branched and heterocyclic chains). Inthis formula " n " is mostly an even number ofcarbon atoms (2-34 ) with a few exceptionsthat have an odd number.Fatty acids are classified according toseveral bases as follows :


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I. According to presence or absence ofdouble bonds they are classified into:

A-Saturated Fatty Acids they contain no double bonds with 2-24or more carbons.They are solid at room temperatureexcept if they are short chained.They may be even or odd numbered.They have the following molecularformula, C nH2n+1 COOH.


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Saturated fatty acids (no double )

A-Short chain Saturated F.A. (2-10carbon).

a-Short chain Saturated volatile F.A.(2-6carbon).b- Short chain Saturated non volatile F.A.(7-

10 carbon).B-Long chain Saturated F.A.(more the10

carbon)


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a-Volatile short-chain fatty acids : They are liquid in nature and contain(1-6) carbon atoms. water-soluble and volatile at roomtemperature, e.g., acetic, butyric, andcaproic acids.Acetic F.A. (2C ) CH 3-COOH.Butyric F.A. (4C ) CH 3-(CH 2)2-COOH.Caproic F.A. (6C ) CH 3-(CH 2)4-COOH.


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b-Non-volatile short-chain fatty acids :They are solids at room temperatureand contain 7-10 carbon atoms. They are water-soluble and non-volatile at room temperature includecaprylic and capric F.A.

caprylic (8 C ) CH 3-(CH 2)6-COOH.Capric (10 C ) CH 3-(CH 2)8-COOH.


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1-Monounsaturated fatty acids : 1-Palmitoleic acid :

It is found in all fats.It is C16:19 , i.e., has 16 carbons andone double bond located at carbonnumber 9 and involving carbon 10.

CH3-( CH

2 )

5CH = CH-(CH

2)

7 COOH


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2-Oleic acid Is the most common fatty acid innatural fats.It is C18:19 , i.e., has 18 carbons andone double bond located at carbonnumber 9 and involving carbon 10.

CH3-(CH

2)

7- CH=CH (CH

2)

7-COOH


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3-Nervonic acid (Unsaturated lignoceric acid).

It is found in cerebrosides.It is C24:1 15 , i.e., has 24 carbons andone double bond located at carbonnumber 15 and involving carbon 16.

CH 3 (CH 2)7 CH= CH (CH 2)13 - COOH


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2-Polyunsaturated fatty acids :

(Essential fatty acids ):Definition: They are essential fatty acids that can

not be synthesized in the human bodyand must be taken in adequateamounts in the diet.

They are required for normal growthand metabolism


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Source: vegetable oils such as corn oil,linseed oil, peanut oil, olive oil,

cottonseed oil, soybean oil and manyother plant oils, cod liver oil and animalfats. Deficiency: Their deficiency in the dietleads to nutrition deficiency disease .Its symptoms include: poor growth andhealth with susceptibility to infections,

dermatitis, decreased capacity toreproduce, impaired transport of lipids,fatty liver, and lowered resistance tostress.


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Function of Essential Fatty Acids: 1. They are useful in the treatment of atherosclerosis

by help transporting blood cholesterol and

lowering it and transporting triglycerides.2. The hormones are synthesized from them.3. They enter in structure of all cellular and

subcellular membranes and the transportingplasma phospholipids.

4. They are essential for skin integrity, normal growth and reproduction.

5. They have an important role in blood clotting(intrinsic factor).

6. Important in preventing and treating fatty liver.7. Important role in health of the retina and vision.8. They can be oxidized for energy production.


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2-Linolenic acid :

C18:3 9, 12, 15, in corn, linseed, peanut, olive,cottonseed and soybean oils.

CH 3-CH 2-CH=CH-CH 2-CH=CH-CH 2-CH=CH-(CH 2)7-COOH


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3-Arachidonic acid: C20:4 5, 8, 11, 14 . It is an important component ofphospholipids in animal and in peanutoil from which prostaglandins are

synthesized .

CH 3-(CH 2)4-CH=CH-CH 2-CH=CH-CH 2-CH=CH-CH 2-CH=CH-(CH 2)3-COOH


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1-Simple LipidsA-Neutral Fats and oils (Triglycerides)

Definition:- They are called neutral because theyare uncharged due to absence of

ionizable groups in it. The neutral fats are the most abundantlipids in nature. They constitute about98% of the lipids of adipose tissue, 30%of plasma or liver lipids, less than 10%of erythrocyte lipids.


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They are esters of glycerol with various fattyacids. Since the 3 hydroxyl groups ofglycerol are esterified, the neutral fats arealso called Triglycerides. Esterification of glycerol with one moleculeof fatty acid gives monoglyceride , and that

with 2 molecules gives diglyceride .

H2C O

C HO

H2C

C

C

O C

R1

R3

R2

O

O

O

+

3 H2O

CH2 OH

C HHO

CH2 OH

HO C R1

O

HO C R3

O

HO C R2

O

Fatty acids Glycerol Triglycerides

(Triacylglycerol)


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TYPES OF TRIGLYCERIDES

1-Simple triglycerides : If the three fatty acidsconnected to glycerol are of the same typethe triglyceride is called simple triglyceride,e.g., tripalmitin.

2-Mixed triglycerides : if they are of differenttypes, it is called mixed triglycerides, e.g.,stearo-diolein and palmito-oleo-stearin. Natural fats are mixtures of mixedtriglycerides with a small amount of simpletriglycerides.

O


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CH 2 O

C HO

CH2

C

C

O C

(CH 2 )14

O

O

O

Tripalmitin(simple triacylglycerol)

CH 3

(CH 2 )14CH 3

(CH2

)14

CH3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2 )16

O

O

O

1-Stearo-2,3-diolein(mixed triacylglycerol)

CH 3

(CH 2 )7CHCH(CH 2 )7CH 3

(CH 2 )7 CH CH (CH 2 )7 CH 3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2 )14

O

O

O

1-palmito-2-oleo-3-stearin(mixed triacylglycerol)

CH 3

(CH 2 )16 CH 3

(CH 2 )7CHCH(CH 2 )7CH 3


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Physical properties of fat and oils:1. Freshly prepared fats and oils are

colorless, odorless and tasteless.Any color,or taste is due to association with otherforeign substances, e.g., the yellow color ofbody fat or milk fat is due to carotenepigments (cow milk) .

2. Fats have specific gravity less than 1 and,therefore, they float on water.

3. Fats are insoluble in water, but soluble in

organic solvents as ether and benzene. 4. Melting points of fats are usually low,

but higher than the solidificationpoint,


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2-Saponification . Alkaline hydrolysisproduces glycerol and salts of fatty acids

(soaps ).Soaps cause emulsification of oily materialthis help easy washing of the fatty materials

CH2 O

C HO

CH2

C

C

O C

R1

R3

R2

O

O

OH2C OH

C HHO

H2C OH

ONaCR1

O

ONaCR3O

+ ONaCR2

O

Triacylglycerol Glycerol Sodium salts of fatty acids (soap)

3 NaOH


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3-HalogenationNeutral fats containing unsaturated fatty acids have

the ability of adding halogens (e.g., hydrogen orhydrogenation and iodine or iodination) at thedouble bonds.- It is a very important property to determine thedegree of unsaturation of the fat or oil thatdetermines its biological value

CH (CH 2 )7 COOHCHCH 2CH

Linoleic acidCH(CH 2 )4CH 3

2 I 2

CH (CH 2 )7 COOHCHCH 2CH

Stearate-tetra-iodinate

CH(CH 2 )4CH 3

II I I


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4-Hydrogenation or hardening of oils :It is a type of addition reactions acceptinghydrogen at the double bonds of unsaturatedfatty acids.The hydrogenation is done under highpressure of hydrogen and is catalyzed byfinely divided nickel or copper and heat.It is the base of hardening of oils ( margarinemanufacturing ), e.g., change of oleic acid offats (liquid) into stearic acid (solid).

It is advisable not to saturate all doublebonds; otherwise margarine produced will bevery hard, of very low biological value anddifficult to digest.


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5-Oxidation(Rancidty)

This toxic reaction of triglyceridesleads to unpleasant odour or taste ofoils and fats developing after oxidationby oxygen of air, bacteria, or moisture.Also this is the base of the drying oilsafter exposure to atmospheric oxygen.Example is linseed oil, which is used inpaints and varnishes manufacturing


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RancidityDefinition:

It is a physico-chemical change in thenatural properties of the fat leading tothe development of unpleasant odor or

taste or abnormal color particularly onaging after exposure to atmosphericoxygen, light, moisture, bacterial orfungal contamination and/or heat.

Saturated fats resist rancidity morethan unsaturated fats that haveunsaturated double bonds.


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Hazards of Rancid Fats :1. The products of rancidity are toxic,

i.e., causes food poisoning andcancer.

2. Rancidity destroys the fat-solublevitamins (vitamins A, D, K and E).

3. Rancidity destroys thepolyunsaturated essential fatty acids.

4. Rancidity causes economical lossbecause rancid fat is inedible.


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Analysis and Identification of fats and oils(Fat Constants)

Fat constants or numbers are tests usedfor:

1. Checking the purity of fat for detection of

adulteration.2. To quantitatively estimate certain properties

of fat.3. To identify the biological value and natural

characteristics of fat.4. Detection of fat rancidity and presence of

toxic hydroxy fatty acids.


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1-Iodine number (or value):Definition : It is the number of grams of iodine absorbed by 100 grams of fat oroil.Uses : It is a measure for the degree ofunsaturation of the fat, as a natural propertyfor it.Unsaturated fatty acids absorb iodine at theirdouble bonds, therefore, as the degree of

unsaturation increases iodine number andhence biological value of the fat increase.It is used for identification of the type of fat,detection of adulteration and determining the

biological value of fat.


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2-Saponification number (or value):Definition : It is the number of milligrams of KOH required to completely saponify onegram of fat .Uses :Since each carboxyl group of a fatty acidreacts with one mole of KOH duringsaponification, therefore, the amount of alkalineeded to saponify certain weight of fatdepends upon the number of fatty acidspresent per weight.

Thus, fats containing short-chain acids willhave more carboxyl groups per gram thanlong chain fatty acids and consume morealkali, i.e., will have higher saponificationnumber.


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3-Acids Number (or value):Definition :It is the number of milligrams of KOH required to neutralize the free fattyacids present in one gram of fat.Uses: It is used for detection of hydrolyticrancidity because it measures theamount of free fatty acids present.


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4-Reichert- Meissl Number (or value):Definition : It is the number of milliliters of 0.1

N KOH required to neutralize the water-soluble fatty acids distilled from 5 grams offat. Short-chain fatty acid (less than 10carbons) is distillated by steam.

Uses : This studies the natural compositionof the fat and is used for detection of fatadulteration.

Butter that has high percentage of short-chain fatty acids has highest Reichert-Meisslnumber compared to margarine.


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5-Acetyl Number (or value):Definition : It is number of milligrams of KOHneeded to neutralize the acetic acid liberatedfrom hydrolysis of 1 gram of acetylated fat (hydroxy fat reacted with acetic anhydride ).Uses: The natural or rancid fat that containsfatty acids with free hydroxyl groups areconverted into acetylated fat by reaction withacetic anhydride. Thus, acetyl number is a measure of numberof hydroxyl groups present. It is used for studying the natural propertiesof the fat and to detect adulteration andrancidity.

B Waxes


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B-WaxesDefinition : Waxes are solid simple lipidscontaining a monohydric alcohol (with ahigher molecular weight than glycerol)esterified to long-chain fatty acids. Examplesof these alcohols are palmitoyl alcohol,cholesterol, vitamin A or D.Properties of waxes : Waxes are insoluble inwater, but soluble in fat solvents and arenegative for acrolein test.

Waxes are not easily hydrolyzed as the fatsand are indigestible by lipases and are veryresistant to rancidity.Thus they are of no nutritional value.


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Type of Waxes :- Waxes are widely distributed in nature such as

the secretion of certain insects as bees-wax,protective coatings of the skins and furs ofanimals and leaves and fruits of plants. They areclassified into true-waxes and wax-like

compounds as follows:A-True waxes : include:

Bees-wax is secreted by the honeybees thatuse it to form the combs. It is a mixture ofwaxes with the chief constituent is mericylpalmitate.


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Differences between neutral lipids and waxes :

Waxes Neutral lipids

1.Digestibility: Indigestible (nothydrolyzed by lipase).

Digestible (hydrolyzed by lipase).

2-Type ofalcohol :

Long-chain monohydricalcohol + one fatty acid.

Glycerol (trihydric) + 3 fatty acids

3-Type of fattyacids :

Fatty acid mainly palmiticor stearic acid.

Long and short chain fatty acids.

4-Acrolein test : Negative. Positive.

5-Rancidability: Never get rancid. Rancidible.

6-Nature atroomtemperature .

Hard solid. Soft solid or liquid.

7-Saponification Nonsaponifiable. Saponifiable.

8-Nutritivevalue :

No nutritive value. Nutritive.

9-Example: Bee & carnuba waxes. Butter and vegetable oils.


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2-Compound LipidsDefinition :

They are lipids that contain additionalsubstances, e.g., sulfur, phosphorus, aminogroup, carbohydrate, or proteins besidefatty acid and alcohol.Compound or conjugated lipids areclassified into the following types accordingto the nature of the additional group:

1. Phospholipids2. Glycolipids.3. Lipoproteins4. Sulfolipids and amino lipids.

A Ph h li id


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A-PhospholipidsDefinition: Phospholipids or phosphatides are

compound lipids, which contain phosphoric acidgroup in their structure .

Importance : 1. They are present in large amounts in the liver and

brain as well as blood. Every animal and plant cellcontains phospholipids.

2. The membranes bounding cells and subcellularorganelles are composed mainly of phospholipids.Thus, the transfer of substances through thesemembranes is controlled by properties ofphospholipids.

3. They are important components of the lipoproteincoat essential for secretion and transport of plasmalipoprotein complexes. Thus, they are lipotropicagents that prevent fatty liver .

4. Myelin sheath of nerves is rich with phospholipids.

5 I i di i d b i f


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5-Important in digestion and absorption ofneutral lipids and excretion of cholesterolin the bile.

6-Important function in blood clotting andplatelet aggregation.7-They provide lung alveoli with surfactants

that prevent its irreversible collapse .

8-Important role in signal transduction acrossthe cell membrane.9-Phospholipase A2 in snake venom

hydrolyses membrane phospholipids intohemolytic lysolecithin or lysocephalin.

10-They are source of polyunsaturated fattyacids for synthesis of eicosanoids.


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Sources: They are found in all cells (plantand animal), milk and egg-yolk in the

form of lecithins.Structure : phospholipids are composed of:1. Fatty acids (a saturated and an

unsaturated fatty acid).2. Nitrogenous base (choline, serine,

threonine, or ethanolamine).3. Phosphoric acid.4. Fatty alcohols (glycerol, inositol or

sphingosine).


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Classification of Phospholipids areclassified into 2 groups according to thetype of the alcohol present into two types:

A-Glycerophospholipids : They are regarded asderivatives of phosphatidic acids that are thesimplest type of phospholipids and include:

1. Phosphatidic acids.2. Lecithins3. Cephalins.4. Plasmalogens.5. Inositides.6. Cardiolipin .B-Sphingophospholipids : They contain

sphingosine as an alcohol and are namedSphingomyelins .


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A-Glycerophospholipids 1-Phosphatidic acids: They are metabolic intermediates

in synthesis of triglycerides andglycerophospholipids in the body and may havefunction as a second messenger . They exist in twoforms according to the position of the phosphate

CH 2 O

C HO

CH 2

C

C

O P

R 1

R 2

O

O

-Phosphatidic acid

OH

OH

O

S a t u r a t e d f at t y a c i d P o l y u n s a t u r a t e d

f at t y a c i d

P h o s p h a t e

CH 2 O

C H

CH 2

C

O

R 1

O

-Phosphatidic acid

S a t u r a t e d f a tt y a c i d

P o l y u n s a t u r a t e d f at t y a c i d

P h o s p h a t e PHOO H

O

C R 2

O

O

2-Lecithins:


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2 Lecithins:Definition : Lecithins areglycerophospholipids that contain choline as

a base beside phosphatidic acid. They existin 2 forms - and -lecithins. Lecithins are acommon cell constituent obtained from brain( -type), egg yolk ( -type), or liver (both

types). Lecithins are important in themetabolism of fat by the liver.Structure: Glycerol is connected at C2 or C3with a polyunsaturated fatty acid, at C1 with

a saturated fatty acid, at C3 or C2 byphosphate to which the choline base isconnected. The common fatty acids inlecithins are stearic, palmitic, oleic, linoleic,linolenic, clupandonic or arachidonic acids.


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Certain cephalins are constituents of the complexmixture of phospholipids, cholesterol and fat thatconstitute the lipid component of the lipoprotein

thromboplastin which accelerates the clotting ofblood by activation of prothrombin to thrombin inpresence of calcium ions .

CH 2 O

C HO

CH 2

C

C

O P

R 1

R 2

O

O

-Cephalin

O

OH

OCH 2 CH 2 NH 2 EthanolamineHO CH 2 CH COO H Serine

NH 2HO CH CH COOH Threonine

NH 2CH 3


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4-Plasmalogens:Definition: Plasmalogens are found in thecell membrane phospholipids fraction ofbrain and muscle (10% of it is plasmalogens),liver, semen and eggs.Structure : Plasmalogens resemble lecithinsand cephalins in structure but differ in thepresence of , -unsaturated fatty alcohol rather than a fatty acid at C1 of the glycerolconnected by ether bond. At C2 there is an unsaturated long-chainfatty acid, however, it may be a very short-chain fatty acid


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Properties : Similar to lecithins .

CH 2

C HO

CH 2

C

O P

R2

O

-Plasmalogen

O

OH

O

CH 2 CH2 N

CH 3

CH 3

CH 3

+

-Unsaturatedfatty alcoholCH CH R 1O


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5-Inositides :Definition :

- They are phosphatidyl inositol. Structure : They are similar to lecithins or cephalinsbut they have the cyclic sugar alcohol, inositol asthe base. They are formed of glycerol, one saturated

fatty acid, one unsaturated fatty acid, phosphoricacid and inositol

CH 2

C HO

CH 2

C

O P

R 2

O

-Phosphatidylinositol

O

OH

O

C R 1OO

H

H

OHO H

HOH

H

OHOH

H H1

2 3

4

56


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Source : Brain tissues .Function :Phosphatidyl inositol is a major componentof cell membrane phospholipids particularlyat the inner leaflet of it. They play a major role as secondmessengers during signal transduction forcertain hormone..On hydrolysis by phospholipase C,phosphatidyl-inositol-4,5-diphosphateproduces diacyl-glycerol and inositol-

triphosphate both act to liberate calciumfrom its intracellular stores to mediate thehormone effects.


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6-Cardiolipins:

Definition : They are diphosphatidyl-glycerol. Theyare found in the inner membrane of mitochondriainitially isolated from heart muscle (cardio). It isformed of 3 molecules of glycerol, 4 fatty acids and 2

phosphate groups .Function : Used in serological diagnosis ofautoimmunity diseases.

CH 2

C HO

CH 2

C

O P

R 2

O

Cardiolipin

O

OH

O

C R 1OO

CH 2

CH OH

CH 2 CH 2

CH O

CH 2

C

OP

R 3O

O

OH

O

CR 4 OO


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Ceramide This part of sphingomyelin in which the


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Ceramide This part of sphingomyelin in which theamino group of sphingosine is attached to the fattyacid by an amide linkage.

Ceramides have been found in the free state in thespleen, liver and red cells.

CH CH NH

CH 2

CHCH(CH 2 ) 12CH 3

OH

Sphingosine

C R 1

O

O

P O

OH

O CH 2 CH 2 N

CH 3

CH 3

CH 3

+

Choline

Fatty acid

Phosphate

Ceramide

Sphingomyelin

B-Glycolipids


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B GlycolipidsDefinition : They are lipids that containcarbohydrate residues with sphingosine as the

alcohol and a very long-chain fatty acid (24 carbonseries).They are present in cerebral tissue, therefore arecalled cerebrosides

Classification : According to the number andnature of the carbohydrate residue(s) present inthe glycolipids the following are

1. Cerebrosides. They have one galactose

molecule (galactosides).2. Sulfatides. They are cerebrosides with sulfate on

the sugar (sulfated cerebrosides).3. Gangliosides. They have several sugar and

sugaramine residues.

1-Cerebrosides:


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Occurrence: They occur in myelin sheath of nerves and whitematter of the brain tissues and cellular membranes. They areimportant for nerve conductance.

Structure : They contain sugar, usually -galactose and may beglucose or lactose, sphingosine and fatty acid, but no phosphoricacid.

CH CH NH

CH 2

CHCH(CH 2 ) 12CH 3

OH

Sphingosine

C R 1

O

O

Psychosin

Fatty acid

Ceramide

Cerebroside

OOH

H HH

OHH

OH

CH 2 OH

HGalactose


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2 S lf id


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2-Sulfatides :They are sulfate esters of kerasin or phrenosin inwhich the sulfate group is usually attached to the OH group of C3 or C6 of galactose. Sulfatides areusually present in the brain, liver, muscles andtestes.

CH CH NH

CH 2

CHCH 2(CH 2 ) 12CH 3

OH

C R 1

O

O

Sulfatides (sulfated cerebroside)

OOH

H HH

OHH

OSO 3 H

CH 2 OH

H

3 G gli id


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3-Gangliosides: They are more complex glycolipids that occur in thegray matter of the brain, ganglion cells, and RBCs.They transfer biogenic amines across the cellmembrane and act as a cell membrane receptor. Gangliosides contain sialic acid (N-acetylneuraminic acid), ceramide (sphingosine + fatty acid of 18-24carbon atom length), 3 molecules of hexoses (1glucose + 2 galactose) and hexosamine. The mostsimple type of it the monosialoganglioside,. It worksas a receptor for cholera toxin in the human

intestine.Ceramide-Glucose-Galactose-N-acetylgalactosamine-Galactose

MonosialogangliosideSialic acid

C Lipoproteins


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C-LipoproteinsDefinition : Lipoproteins are lipids combined withproteins in the tissues. The lipid component is

phospholipid, cholesterol or triglycerides. Theholding bonds are secondary bonds.They include:

1. Structural lipoproteins : These are widely distributedin tissues being present in cellular and subcellular

membranes. In lung tissues acting as a surfactant ina complex of a protein and lecithin. In the eye,rhodopsin of rods is a lipoprotein complex.Transport lipoproteins :These are the forms present in blood plasma. They

are composed of a protein called apolipoprotein anddifferent types of lipids. (Cholesterol, cholesterolesters, phospholipids and triglycerides). As the lipidcontent increases, the density of plasmalipoproteins decreases

Cholesterol:


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Importance: - It is the most important sterol in animal tissues as

free alcohol or in an esterified form ( with linoleic ,oleic, palmitic acids or other fatty acids ). Steroid hormones, bile salts and vitamin D arederivatives from it. Tissues contain different amounts of it that serve astructural and metabolic role, e.g., adrenal cortex content is 10%, whereas, brain is 2%, others 0.2-0.3%. Source: - It is synthesized in the body from acetyl-CoA (1gm/day, cholesterol does not exist in plants)and is also taken in the diet ( 0.3 gm/day as in, butter,milk, egg yolk, brain, meat and animal fat).

Physical propeties: It has a hydroxyl group on C3 a


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Physical propeties: It has a hydroxyl group on C3 , adouble bond between C5 and C6, 8 asymmetric carbon atoms and a side chain of 8 carbon atoms .

It is found in all animal cells, corpus luteum andadrenal cortex, human brain (17% of the solids).In the blood (the total cholesterol amounts about 200mg/dL of which 2/3 is esterified , chiefly to

unsaturated fatty acids while the remainder occursas the free cholesterol .

CH 3

CH 3

HO

CH 3CH 3

CH 3

Cholesterol

h l


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Chemical properties Intestinal bacteria reducecholesterol into coprosterol and dihydrocholesterol .- It is also oxidized into 7-Dehydrocholesterol andfurther unsaturated cholesterol with a second doublebond between C7 and C8. When the skin isirradiated with ultraviolet light 7-dehydrocholesterolis converted to vitamin D3. This explains the valueof sun light in preventing rickets.

CH 3

CH 3

HO

CH 3CH 3

CH 3

Coprosterol,in feces

H

CH3

CH 3

HO

CH 3CH 3

CH 3

Dihydrocholesterol,in blood and other tissues

H

E l


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Ergosterol differs from 7-dehydrocholesterol inthe side chain. Ergosterol is converted to vitamin D2by irradiation with UV Ergosterol and 7-dehydrocholesterol are called Pro-vitamins D orprecursors of vitamin D.- It was first isolated from ergot, a fungus then fromyeast. Ergosterol is less stable than cholesterol(because of having 3 double bonds ).

CH3

CH3

HO

CH3CH3CH3

7-dehydrocholesterol

CH3

CH3

HO

CH3CH3CH3

Ergosterol

CH3

Steroids


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Steroids constitute an important class ofbiological compounds.

Steroids are usually found in associationwith fat. They can be separated from fatsafter saponification since they occur in theunsaponifiable residue. They are derivatives of cholesterol that isformed of steroid ring or nucleus. Biologically important groups of substances, whichcontain this ring, are:

1. Sterols.

2. Adrenal cortical hormones.3. Male and female sex hormones.4. Vitamin D group.5. Bile acids.6. Cardiac glycosides.


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Bile acids :Th d d f id ti f h l t l i


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They are produced from oxidation of cholesterol inthe liver producing cholic and chenodeoxycholicacids that are conjugated with glycine or taurine toproduce glycocholic, glycochenodeoxycholic,taurocholic and taurochenodeoxycholic acids. Theyreact with sodium or potassium to produce sodium or potassium bile salts .Their function is as follows :

1. Emulsification of lipids during digestion.2. Help in digestion of the other foodstuffs.3. Activation of pancreatic lipase.4. Help digestion and absorption of fat-soluble

vitamins.5. Solubilizing cholesterol in bile and prevent gall stoneformation.6. Choleretic action (stimulate their own secretion).7. Intestinal antiseptic that prevent putrefaction


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CH3

CH3

HO

CH3

C

Sodium-tauro or glyco-cholate

CH3

CH3

HO

CH3

C

Sodium-tauro or glyco-chenodeoxycholate

OH

OH OH

O O

R1 or R 2 R1 or R 2

(CH2)2

SO3

-Na +H2NCH2 COO

-Na +H2N

Sodium taurateSodium glycateR1 R

2


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BioChem I - 05. Lipid.ppt