JAIPUR NATIONAL UNIVERSTY,JAGATPURA,JAIPUR

DNA Replication

Name :-Arihant jain Department of life scienceM.Sc. Microbiology 2nd Semester

GENETIC INFORMATION TRANSFER

DNA

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Replication of eukaryotes Chromosome of eukaryotes have multiple

origins. The space between 2 adjascent origins is

called the replicon, a functional unit of replication.

Orgin of DNA replication (every-150 kb)

Semi-continuous Replication The daughter strands on 2 template strands

are synthesized differently since the replication process obeys the principle that DNA is synthesized from the 5’ to the 3’ end.

OKAZAKI FRAGMENTS:-Many DNA fragments are synthesized sequentially on the DNA template strand having the 5’ end. These DNA fragments are called Okazaki fragments. They are 100-150 nucleiotide long for eukaryotes

On the template having the 3’ end the daughter strand is synthesized continuouslyin the 5’-3’ direction. This strand is referred as the leading strand.The daughter strand consisting of okazaki fragments is called the lagging strand.Continuous synthesis of the leading strand & discontinuous synthesis of lagging strand represent a unique feature of DNA replication,its referred as semi-continuous replication.

Primase (DnaG)

Primase is able to synthesize primers using free NTPs as the substrate & the ssDNA as the template.

Primers are short RNA fragments of a several decades of nucleotides long.

Helicase (DnaB) It opens the dsDNA with consuming ATP. The opening process with the assistance of

DnaA & DnaC

SSB Protein Stand for ssDNA binding protein. SSB Protein maintain the DNA Template in the

single strand form order to -prevent the ds DNA formation; -protect the vulnerable ssDNA from

nucleases.

Topoisomerase

Opening the ds DNA will create supercoil ahead of replication forks.

The supercoil constraint needs to be released by topoisomerase.

DNA Ligase

Connect 2 adjascent ssDNA strands by joining the 3’-OH of one DNA strand to the 5’-P of another DNA strand.

Sealing the nick in the process of replication , repairing, recombination & splicing

Replication Fedelity

Replication based on the principle of base pairing is crucial to the high accuracy of the genetic information transfer.

Enzymes use 2 mechanism to ensure the replication fidelity.

-Proofreading & real-time correction

-Base selection

DNA Replication in Eukaryotes DNA replication is closely related with the cell

cycle. Multiple origin on 1 chromosome replications

are activated in a sequential order rather than simultaneously

INITIATION

Elongation

Termination

Telomerase

Significance of telomerase:-

Telomerase may play important role in cancer cell biology & in cell aging

References:- Book reference:-

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