DNA REPLICATION

Prepared by ,NAVEENA GIRISHSTUDENT OF CENTRAL UNIVERSITY OF KERALAKASARAGOD

REQUREMENTS -dNTPs , template enzymes, proteins3’ oh end , primer ,mg2+

DNA REPLICATION IS A SEMI CONCERVATIVE SYNTHESIS OF DAUGHTER STRAND,EACH PARENTAL STRAND

SERVES AS TEMPLATE

Previous 3 models

concervative

• Original fully concerved

dispersive

• Fragmented and old and new one mixed

Semi concerva

tive

• Each strand template

• Widely accepted

Meselson and stahl

Semi concervative -evidence

Models of replication

model DNA template

Breakage of strand

Number of replicons

Uni/bidirectional

e.g. products

theta no 1 Uni/bi Bacteria

Rolling circle

yes 1 uni virus,F

Linear eukaryotic

yes many Bidirectional eukaryotic

DNA POLYMERASE ARTHUR KONBERG-ECOLI

ACTUALLY DOES REPAIR –KONBERG ENZYME

HELP TO ELONGATE DNA STRAND

IT CAN POLYMERASE 5’-3’ DIRECTION

ONLY ADD IN PRESENCE OF PRIMER

PROKARYOTIC POLYMERASE POLYMERASE ш IMP

1ST ,2ND AND 3RD

EUKARYOTIC POLYMERASEothers –repair and recombination

IN MITOCHONDRIAL DNA REPLICATION

in nuclear AND PRIMASE ACTIVITY

IN NUCLEAR,IN LAGGING STRAND

NUCLEAR , LEADING STRANDREPLICATION

High fidelity- high specific active sites and repair mechanism

Escaped errors –leads to mutation

Proof reading

Mismatch repair

REPLICATION FORK

Replication fork – point of unwinding and active DNA synthesis

Experiment- Ecoli - john cairns -RADIOACTIVE –THYMIDINE-autoradiography-replication bubble -2 replication forks

Replication happens in the direction of unwinding

5’-3’ direction –leading strand

3’-5’ –lagging strand-composed of okazaki fragments

-Reiji okazaki discovered it

Prokaryotic DNA replication

INITIATION AND UNWINDING

ONLY 1 ORI

INTIATOR PROTEIN JUST UNWIND

HELICASE- UNWINDING ENZYME

HELICASE BIND LAGGING STRAND –MOVE 5’ TO3’ BY BREAKING H BOND

SSB PROTEINS –PREVENT SUPER COILING AND REVERSIONING

DNA GYRASE-TOPOISOMERASE –REDUCE TORQUE( 1st and 2nd )

PRIMASE+ HELICASE=COMPLEX PRIMING ACTIVITY AND UNWINDING

ELONGATION AND TERMINATIONSLIDING CLAMB AND CLAMB LOADING PROTEIN BOUND ; POLYMERISEш- ELONGATION AND EXONUCLEASE ACTIVITY

B POLYPEPTIDE CLAMP HELP TO ATTACH TO TEMPLATE

DNA POLYMERASE 1 - EXO NUCLEASE ,REMOVE PRIMERS

DNA POLYMERASE 2,4,5 DNA REPAIR

DNA POLYMERASE

5’-3’ POLYMERIZATION

3’-5’ EXO NUCLEASE

5’-3’ EXO NUCLEASE

FUNCTION

Ì YES YES YES REPLACE PRIMER

2 YES YES NO DNA REPAIR

3 YES YES NO ELONGATES DNA

4 YES NO NO DNA REPAIR

5 YES NO NO DNA REPAIR

DNA LIGASE – JOINS OKAZAKI FRAGMENTS BY NICKS

TERMINATION- 2FORKS MEET/TERMINATION PROTEIN BIND TO HELICASE

PROOF READING 3’-5’ direction

MIS MATCH REPAIR

Eukaryotic replication

DNA polymerase activity

Helicase , topoisomerase, replication protein A bind

Replication licensing factor - mini chromosome maintenance –bind

A multiprotein origin-recognition complex binds to initiate the unwinding of the DNA

They are autonomously replicating sequences( AT) rich

Many ORIGIN OF REPLICATION

Linear and large genome

After DNA Replication ,new nucleosomes reassemble on the DNA quickly

Nucleosomes apparently break

Reassemble from a random mixture of old and new histones

Location of replication –replication factories

TELOMERASE LINEAR GENOME FACES GAP AT IT S END AFTER REMOVING THE PRIMERSRESPONSIBLE FOR AGING

PROTEIN RNATELOMER

ASE ENZYME

RNA PART 15-20 NUCLEOTIDES

IT EXTENDS PROTRUDING STRAND

PRIMER REMOVES AND GAP IS FILLED BY ALPHA- POLYMERASE / TELOMERES FOLD BACK FOR UNCONVENTIONAL BASE PAIRING

REPLICATION AND CELLCYCLE PROKARYITE –CONTINUOS

EUKARYOTE –AFTER G1 –IN S PHASE

LICENCING SYSTEM RESTRICT REPLICATION AFTER THAT

THANK YOU