HUMAN DNA POLYMERASE

INTRODUCTION

DEFINATIONA DNA polymerase is an enzyme that catalyzes the polymerization of deoxyribonucleotides into a DNA strand FAMILIESDNA polymerase is further subdivided into seven families A,B,C,D,X,Y,R,T

EUKARYOTIC DNA POLYMERASE ;Eukaryotes there are five DNA polymerases: alpha, beta, gamma, delta, and epsilon which are responsible for different reactions of DNA synthesis.

•eukaryotes there are five DNA polymerases: alpha, beta, gamma, delta, and epsilon which are responsible for different reactions of DNA synthesis.

FIVE IMPORTANT DNA POLYMARASEPol α 

multisubunit, with the subunits acting as a primase (synthesizing an RNA primer), and then with DNA Pol α elongating that primer with DNA nucleotides. After around 20 nucleotides elongation is taken over by Pol ε (on the leading strand) and δ (on the lagging strand).

Pol β: Implicated in repairing DNA, in base excision repair and gap-filling

synthesis.Pol γ

: Replicates and repairs mitochondrial DNAand has proofreading 3'->5' exonuclease activity.

Pol δ: Highly processive and has proofreading 3'->5' exonuclease activity. It is

the main polymerase involved in lagging strand synthisesPol ε:

It has proofreading 3'->5' exonuclease activity. Highly related to pol δ, and it is the main polymerase involved in leading strand synthesis,.

PROPERTIES

DNA polymerase works at very high pace .it adds 2000 neucleotide bases per sec in prokyreotes and 1000 bases per sec in eukyreotes.

It always needs a primer sequence of 20 neuleotide bases for initiation of replication.

It is not able to initiate the replication process. It can only elongates the primer by adding neucleotide bases.

DNA polymerase always moves in 5’-3’ direction .

STRUCTURE

DNA polymerase is akin to human hand

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DNA polymerase is a dimer

FUNCTION

DNA REPLICATION

DNA PROOFREADING

DNA REPAIR

PROOF READING

Error correction the property of some but not all of DNA Polymerase this process corrects mistakes in newly synthesized DNA when incorrect base is recognized DNA POL moves backwards by one base pair .the 3’-5’ exonuclease activity of enzyme allow incorrect base pair to be excised .The polymerase can re-insert the correct base and replication forwards.

REPLICATION

Once primase has created the RNA primer DNA Pol alpha elongates that primer with DNA neucleotides after around 20 nucleotides elongation is taken over by Pol eta at leadind strand and by Pol delta on lagging strand.

DNA REPAIR

Any damage or change occurred in DNA is recovered by DNA polymerase .it will add correct bases in damaged part and borken bonds are again formed.in this way structure of DNA is recovered again.

IMPORTANCE

Having its role in DNA replication DNA polymerase holds great importance for existance of life.

in Cell divison it confirms the exact copy of genome.

Due to its proof reading ability it eliminat many kind of mutations including point mutation caused by wrong insertion of any one base .or the mutations caused by deletion, addition, translocation and inversion .

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