Molecular Biology in Medicine.2014

8/21/2019 Molecular Biology in Medicine.2014

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MOLECULARBIOLOGY IN

MEDICINEA. A. Osuntoki, Ph.D.


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Molecular biology involves the study of DNA andRNA, the role of these molecules in biological

systems and how interaction(s) with othermolecules and / or environmental factors affecttheir function.

The primary role of DNA is to carry genetic

information. There are various forms of RNA and they have

various roles in protein synthesis.


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WHAT IS GENETICS ?

The study of heredity and variations.

The study of how characteristics are

passed from parents to offspring.Also studies how new traits arise.


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GENETICS AND CLINICAL PRACTICE

Genetic variation is linked to many humandiseases.

Some 4000 genetic diseases have been identified

Genetics is becoming an integral part of healthcare in all medical specialties.

Clinician are at the interface of science and care

Lack of genetic training is a common problem forhealth professionals.


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Knowledge of genome structure and

function coupled with advances in DNAtechnology are aiding the development ofnovel diagnostic and treatment strategies.

There is a need to understand the basics

as genome technologies move from thebench to the clinic.


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THE CHROMOSOME

A nucleoprotein complex

Contains the genetic material

Polygenic Consists of DNA and basic proteins

The protein kind and types may vary in

different cell types Twenty three (23) pairs in humans


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THE GENE

Contained on the chromosome

The unit of heredity

Finite sequence of nucleotides

In eukaryotes, each cell contains the full genetic complement

(exception: mature rbc)

Made up of DNA in most life forms

Contains information for the blueprint for the organism

Sequence of DNA capable of independent expression

The major function is to specify the sequence of amino acids in aprotein

Determines the structure of a protein

Must be expressed to perform its biological roles.

Specific genes determine hereditary traits


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DEOXYRIBONUCLEIC ACID (DNA)

Is the store of genetic information in all life forms exceptsome viruses where RNA is the genetic material

Double stranded helix

The two strands are anti-parallel The structure is stabilized by hydrogen bonds between

base pairs (AT, GC)

The double stranded chain structure ensuresinformation retrieval in case of damage to a strand.

In the cell DNA serves as a template for its ownreplication and as a template for RNA synthesis.


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BASE PAIRING IN DNA


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DNA STRUCTURE


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THE GENETIC CODE

Genetic information is organized into genes or cistrons

The message is encoded in a triplet of bases called codons

Codons specify the amino acids to be incorporated into agrowing protein chain

Codons also specify chain termination

There are 64 codons

61 codons specify amino acids

3 codons specify chain termination

The code is degenerate The code is universal


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RIBONUCLEIC ACID(RNA)

A close chemical relative of DNA.

The major difference is the absence of oxygenat the 2Iposition of the sugar-phosphate

backbone of DNA which is present in RNA. RNA is single stranded while DNA is double

stranded.

Present in several different forms in living cells

* messenger RNA (mRNA)* transfer RNA (tRNA)

* ribosomal RNA (rRNA)


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GENE EXPRESSION

A gene is said to be expressed when the

gene product is being produced.

The flow of genetic information is depicted

below:

DNA RNA PROTEIN

i ii


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The implication is that DNA makes RNA which in turn makesproteins.

This is what is generally referred to as the Central dogma ofgene expression.

The formation of daughter DNA strands is called replication.This process is semiconservative i.e. a strand in a new pairis newly formed while the other is inherited.

The transfer of genetic information to RNA (i) is calledtranscription. All RNA types are transcribed from DNA.

The conversion of the genetic information into a polypeptide(ii) is called translation.


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REPLICATION

Replication is semiconservative.

Starts at a unique origin and proceeds inopposite directions.

Both strands serve as templates. DNA synthesis is primed by RNA.

One strand is synthesized discontinuously.

DNA polymerase takes instruction from the

template. DNA polymerase corrects mistakes during

replication.


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TRANSCRIPTION

Only one strand of DNA is transcribed in aparticular region of the genome.

Direction of synthesis is 51 31like that of DNA.

Transcription is initiated at promoter sites on theDNA template.

RNA polymerase takes instructions from a DNAtemplate.

Many RNA molecules undergo post-transcriptional modifications.


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TRANSLATION

The conversion of the information in a gene intoa protein molecule.

The process of reading the genetic code.

Takes place in the ribosome. mRNA is the template.

The tRNAs carry amino acids in the activatedform to the ribosome for incorporation into a

nascent chain. AUG is the start codon while UUA, UAG and

UGA are stop codons.


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PHENOTYPES ANDGENOTYPES

Phenotypes : All the observablecharacteristics of an individual

Traits: refer to the single characteristic of the

individual

Genotypes: The genes that make up thechromosomes showing a characteristic trait

Genes contain the actual code for traits Alleles: variations of a gene that relate to the

same characteristic are called alleles


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GENETIC DISORDERS

Genetic disorders can result from:

Abnormal chromosome numbers Changes in the reading frame caused by

deletions and insertion

Changes in nucleotide sequence


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MUTATION ANDDISEASES

The information carrying function of DNArequires the protection of the integrity of themolecule.

It is apparent that faithful transmission(copying) of the information at eachgeneration is essential for preserving the

characteristics of organisms..


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Mutation contd

A nucleotide sequence alteration may

change the composition of nucleotides in a

codon, or affect the way the gene is read.This may result in the incorporation of an

incorrect amino acid into the protein .

A mutation may have significant effects on

the organism or may be harmless


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mutation contd..

An altered amino acid sequence may greatly affect the abilityof the protein to perform its biological role.

The chemical and physical features (including the structure)of a protein result from the arrangement and composition of

amino acids in the chain. The function of biological molecules is intrinsically linked to

the structure. Thus, the replacement of even a single aminoacid with another may diminish the capacity of a protein tofunction or inactivate it.

The end results are genetic defects which may manifest withnegative impacts on the health of individuals.


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Alterations in the nucleotide sequence results inmutation

There are two broad classifications of mutation- Point mutation (single base substitution)

- Frame shift mutation (indel)

Mutation contd


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If one purine [A or G] or pyrimidine [C or T] is replaced by theother, the substitution is called a transition

If a purine is replaced by a pyrimidine or vice-versa, the

substitution is called a transversion

Samesense: The mutation results in the formation of a codonthat is a synonym of the wild type

Missense:The mutation alters the codon to produce an

altered amino acid in the protein product Nonsense: The mutation changes a codon for an amino acid

into a stop codon

POINT MUTATION


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Insertion

Deletion

FRAMESHIFT MUTATION


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GENETICS AND DRUG THERAPY

Virtually every human ailment, except

perhaps trauma, has some genetic basis.

Genetic variation can affect the ability ofindividuals to respond effectively to

medication.

This may result in adverse drug reaction orpoor drug response.


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Genetic polymorphism is important not only indetermining the predisposition to diseases butalso for determining an individuals ability tometabolize different therapeutic agents given foralleviating disease severity.

PHARMACOGENETICS: Examines the linkbetween genes and drug response.

PHARMACOGENOMICS: Examines the inherited

variations in genes that dictate drug response andexplores ways in which these variations can beused to predict a patients response to a drug.

GENETICS AND DRUG THERAPY


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PHARMACOGENOMICS

The aim is to improve the overall process of

drug development and develop products

that will benefit the largest population. The ultimate goal is to provide new

strategies for optimizing drug therapy

based on each patients genetic

determinants of drug efficacy and toxicity.


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PROSPECTS OF PHARMACOGENETICS

Personalized medications

More powerful drugs

Better, safer drugs the first time More accurate determination of appropriate

drug doses

Improvements in the drug discovery andapproval process

Decrease in health care costs.


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CLONING

Transfer of a gene from one cell to the other.

Method for purifying, propagating and amplifying aspecific DNA sequence or gene.

The cloned fragment is placed under the geneticexpression machinery of a suitable host cell.

The extraneous DNA is faithfully copied.

The cloned DNA is inherited by the clone cell line.

Possible because of the universality of the geneticcode.


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DNA AMPLIFICATION DNA amplification protocols enable the scientist to

increase the copy of number of a gene or DNA ofinterest.

Unlike in cloning, the chromosome does not haveto be fragmented and extensive purification maynot be carried out.

The most commonly used amplification protocol isthe polymerase chain reaction (PCR).

PCR is a primer directed in vitro DNAamplification protocol which requires knowledge of

the nucleotide sequences of the flanking regionsof a gene / region of interest for primer synthesis.


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POLYMERASE CHAIN REACTION(PCR)

PCR is a primer directed enzymaticamplification process

It enables the amplification of specific DNA

sequences The target sequence is defined by the primers

The sequences of the flanking regions to thetarget site must be known

The primers are complementary to the flankingregions


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PCR: A POWERFUL TOOL

PCR is one of the most powerful laboratory toolsavailable

It possesses a unique combination of attributes

It can be carried out with comparative ease It is sequence specific

It is sensitive

It is flexible

It is relatively cheap

Permits rapid amplification of template DNA


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APPLICATIONS OF PCR

Due to the simplicity and versatility, PCRhas become ubiquitous and with a widerange of general applications

The application will be considered under 3broad headings:

Clinical applications

Forensic applications Research applications


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CLINICAL APPLICATIONS

There are three primary diagnostic applications

Genotyping

Detecting unknown mutations

Detecting pathogens

Other areas of possible use include:

Tissue typing

Blood typing


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OTHER USEFUL TECHNIQUES

GENE THERAPYClinical intervention involving the transfer of a gene into apatient with the aim of correcting a genetic disease.

ANTISENSE TECHNOLOGYThis utilizes oligonucleotide sequences designed to becomplementary to a specific gene sequence to alter geneexpression. The aim is to prevent protein expression from a

targeted sequence.


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GENOMICS AND PROTEOMICS

Genomics and proteomics seek to decipher thefundamental biology of living organisms and to usethe information to enhance the quality of life

The study of genomes is called genomics An organisms complete set of DNA is known as itsgenome.

A genome is the total genetic complement of anorganism.

DNA is the molecule that contains the instruction forthe structure and function of nearly every life form.

Genetic information is determined by the sequenceof nucleotides in a DNA molecule.


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GENOMICS AND PROTEOMICS CONTD.

Proteins make up the body structures and are involved in numerouscellular processes.

Alterations in the sequence of nucleotides in a DNA (mutation) cangenerate abnormal proteins with altered functions leading todiseases.

Sequencing of DNA is a useful technique of detecting variations andmutations which may play a role in the development/ progression ofa disease and in drug response and adverse drug reactions.

The complete DNA sequences of the genomes of many organismsare available.

The genomic data along with proteomics and the tools ofbioinformatics and computational biology enable detailed studies ofgenes and an understanding of the properties of the encodedproteins.


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CONCLUSION

A thorough understanding of the molecular basis of

heredity will ultimately reveal how various elements

interact to affect the human body in health and

disease. There is a promise of a tomorrow wherediagnosis will be exact and the drugs prescribed

more effective and far less likely to induce adverse

drug reactions.


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Molecular Biology in Medicine.2014