Gene Anatomy

Three Major processes in cellular Three Major processes in cellular utilization of genetic information:utilization of genetic information:– Replication: copying of parent DNA to Replication: copying of parent DNA to

form daughter DNA molecule having form daughter DNA molecule having identical nucleotide sequence.identical nucleotide sequence.

– Transcription: part of the coded Transcription: part of the coded message in DNA is copied precisely in message in DNA is copied precisely in the form of RNA.the form of RNA.

– Translation : genetic message coded in Translation : genetic message coded in RNA is translated on the ribosome into a RNA is translated on the ribosome into a protein with a specific sequence of protein with a specific sequence of amino acids.amino acids.

GeneGene

The fundamental unit of information The fundamental unit of information in living system is the gene.in living system is the gene.

A gene is defined as a segment of A gene is defined as a segment of DNA that encodes the information DNA that encodes the information required for the synthesis of required for the synthesis of functional biological product or functional biological product or affects a single character or affects a single character or phenotype ( visible property). phenotype ( visible property).

DNADNA

DNA is vast information database.DNA is vast information database.

It resides in the core of the nucleus It resides in the core of the nucleus of each bodyof each body’’s trillions of cells.s trillions of cells.

It carries the complete set of It carries the complete set of instructions for making all the instructions for making all the proteins a cell will ever need.proteins a cell will ever need.

Chemical Bases in DNAChemical Bases in DNADNA exists as two DNA exists as two long,paired strands long,paired strands spiraled into double spiraled into double helixhelixEach strand is made up Each strand is made up of millions of chemical of millions of chemical bases.bases.There are only four There are only four different chemical different chemical bases bases (adenine A ,thymine (adenine A ,thymine T,cytosine C, guanine G)T,cytosine C, guanine G)

The order in which the The order in which the bases occur determines bases occur determines the messages to be the messages to be conveyedconveyed

Watson & Crick ModelWatson & Crick Model Two helical polynucleotide Chains(strand),run Two helical polynucleotide Chains(strand),run

in opposite direction.in opposite direction. Plan of the bases are perpendicular to helical Plan of the bases are perpendicular to helical

axis.axis. Helical structure repeats itself every 10.6 Helical structure repeats itself every 10.6

residues.residues. Two chains are held together by hydrogen Two chains are held together by hydrogen

bonds & stacking of the bases.bonds & stacking of the bases. The precise sequence of bases carries the The precise sequence of bases carries the

genetic information.genetic information. Always one base is purine while the other is Always one base is purine while the other is

pyrimidine.pyrimidine.

Two helical polynucleotide Chains(strand),run Two helical polynucleotide Chains(strand),run in opposite direction.in opposite direction.

Plan of the bases are perpendicular to helical Plan of the bases are perpendicular to helical axis.axis.

Helical structure repeats itself every 10.6 Helical structure repeats itself every 10.6 residues.residues.

Two chains are held together by hydrogen Two chains are held together by hydrogen bonds & stacking of the bases.bonds & stacking of the bases.

The precise sequence of bases carries the The precise sequence of bases carries the genetic information.genetic information.

Always one base is purine while the other is Always one base is purine while the other is pyrimidine.pyrimidine.

Introduction of supercoilingIntroduction of supercoiling

Most DNA superhelices in Most DNA superhelices in nature are negatively nature are negatively supercoiled, to form a supercoiled, to form a supercoil, three steps are supercoil, three steps are required:required:

Cleavage of one or both DNA strandsCleavage of one or both DNA strands

Passage of one segment of DNA Passage of one segment of DNA through this breakthrough this break

Resealing of the break.Resealing of the break.

Most DNA superhelices in Most DNA superhelices in nature are negatively nature are negatively supercoiled, to form a supercoiled, to form a supercoil, three steps are supercoil, three steps are required:required:

Cleavage of one or both DNA strandsCleavage of one or both DNA strands

Passage of one segment of DNA Passage of one segment of DNA through this breakthrough this break

Resealing of the break.Resealing of the break.

TopoisomeraseTopoisomerase

Two types of topoisomerasesTwo types of topoisomerases– Type 1 topoisomerases: creates a single Type 1 topoisomerases: creates a single ––

stranded breaks in DNA. In prokaryotes stranded breaks in DNA. In prokaryotes removes negative supercoils while in removes negative supercoils while in eukaryotes both negative & positive eukaryotes both negative & positive supercoils can be removed. Important supercoils can be removed. Important only in repair of damaged DNA & in only in repair of damaged DNA & in transcription.transcription.

– Type 11 topoisomerases: cuts double Type 11 topoisomerases: cuts double stranded DNA.stranded DNA.

Prokaryotes-DNA gyrase.Prokaryotes-DNA gyrase.Eukaryotes- it is involved in resolving the Eukaryotes- it is involved in resolving the tangles that exist in newly replicated linear tangles that exist in newly replicated linear chromosome.chromosome.

DNA GyraseDNA Gyrase Introduces negative supercoiling Introduces negative supercoiling

converts the energy of ATP into converts the energy of ATP into torsional energy of supercoilingtorsional energy of supercoiling

Wraping of 200 bp around the enzymeWraping of 200 bp around the enzyme Binding of ATP which trigers cleavage of Binding of ATP which trigers cleavage of

strandsstrands Segment of DNA pass through the gap of the Segment of DNA pass through the gap of the

2 fixed ends2 fixed ends Linking of the two strandsLinking of the two strands Hydrolysis of bound DNA leads to release of Hydrolysis of bound DNA leads to release of

segmentsegment Novobiocin inhibits bacterial gyrase but not Novobiocin inhibits bacterial gyrase but not

eukaryotic gyrase by blocking the binding of eukaryotic gyrase by blocking the binding of ATPATP

Introduces negative supercoiling Introduces negative supercoiling converts the energy of ATP into converts the energy of ATP into torsional energy of supercoilingtorsional energy of supercoiling

Wraping of 200 bp around the enzymeWraping of 200 bp around the enzyme Binding of ATP which trigers cleavage of Binding of ATP which trigers cleavage of

strandsstrands Segment of DNA pass through the gap of the Segment of DNA pass through the gap of the

2 fixed ends2 fixed ends Linking of the two strandsLinking of the two strands Hydrolysis of bound DNA leads to release of Hydrolysis of bound DNA leads to release of

segmentsegment Novobiocin inhibits bacterial gyrase but not Novobiocin inhibits bacterial gyrase but not

eukaryotic gyrase by blocking the binding of eukaryotic gyrase by blocking the binding of ATPATP

DNA MoleculeDNA Molecule

Every human cell contains the same Every human cell contains the same DNADNA

Each cell has 46 molecules of double Each cell has 46 molecules of double stranded DNAstranded DNA

Each DNA molecule is made up of 50 Each DNA molecule is made up of 50 to 250 million bases housed in a to 250 million bases housed in a chromosomechromosome

Gene SubunitsGene Subunits

The gene is the working subunit of The gene is the working subunit of DNADNA

A gene is a segment along the DNA A gene is a segment along the DNA carrying a particular set of carrying a particular set of instructioninstruction

There are between 35000 and 50000 There are between 35000 and 50000 genesgenes

Every gene is made up of thousands, Every gene is made up of thousands, even hundreds of thousands of baseseven hundreds of thousands of bases

Genes in the NewsGenes in the NewsWhat is the connection between What is the connection between gene discoveries and cancergene discoveries and cancer

Is there a connection between Is there a connection between genes and cancergenes and cancer’’s diagnosis or s diagnosis or treatmenttreatment

The answer lies in The answer lies in – Understanding gene discoveriesUnderstanding gene discoveries– The science behind gene testingThe science behind gene testing– The ability to identify changes within The ability to identify changes within

genesgenes