DNA REPLICATION

RITTU CHANDELJR(MD BIOCHEMISTRY)30-04-2013

REPLICATION

•A process in which DNA copies itself to produce identical daughter molecules of DNA

•It is carried out with high fidelity

MESELSON AND STAHL EXPERIMENT

conclusion:

Semiconservative replication

REPLICATION begins at origin; proceeds bidirectionaly

1.Cairns experiment:Both DNA strands replicate simultaneously

2.Inman’s denaturation technique

DNA synthesis is SEMIDISCONTINUOUS

DNA POLYMERASE3 important properties

Bacteria- 5 polymerases

Dna polymerase1

3 ' - 5 ' and 5 ' - 3 ' exonuclease activity5 ' - 3 ' endonuclease activityKlenow fragment

When DNA polymerase can replicate DNA

why other enzymes required?

REPLICATION- very accurate

DNA POLYMERASE 3(replicase)-main replication enzyme

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1. initiation

•elongation

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Final step in synthesis of lagging strands

3.termination

MEMBRANE BOUND REPLICATION

DNA replication IN EUKARYOTES1. CELL CYCLE

2. ORIGIN OF REPLICATION

Why many origin of

replication?

150 hrs in comparison to

9 hrs

3. EUKARYOTIC DNA POLYMERASE

• Eukaryotic enzymes• PCNA• RFC(replication factor C)• MCM

• Prokaryotic counterparts• Β sliding clamp• Γ complex (clamp loader)• helicases

4. REPLICATION

Primase associated with pol α—produces RNA primer

Adds deoxynucleotides to RNA and dissociates from template

Pol δ adds deoxynucleotides on both leading as well as lagging strand

REPLICATION AT ENDS OF CHROMOSOME

DIFFERENCE • PROKARYOTIC

REPLICATION1. Initiation point

specific(ori)2. DNA poly-1,2,3,4,53. No mitochondria4. Replication with only 1

replication fork5. Theta structure observed6. Only unwinding takes

place7. RNA as primer8. Okazaki fragments are

large

• EUKARYOTIC REPLICATION

1. Many ori2. Many types-α, β, γ, δ, ε3. γ DNA polymerase

found in mitochondria4. Many replication forks5. Theta structure not

observed6. Histone seperation as

well as unwinding7. RNA/DNA as primer8. Okazaki fragments are

small

Inhibitors of DNA replication

•That affect either template or priming ability of the growing strand

1. Intercalating agents-anthracyclins(daunorubicin,doxorubicin)

2. Chain breakage-bleomycin3. Interstrand crosslinks-

mitomycin,nitrogen mustard

•Act directly on polymerase or other enzymes

1. Acyclovir2. DNA gyrase inhibitor-nalidixic acid3. Topoisomerase 1 inhibitor- quinolone

BIBLIOGRAPHY•SATYANARYAN•VASUDEVAN•RANA SHINDE•LIPPINCOTT•HARPER•LEHNINGER•BHAGVAN•MARKS•VOET THANK YOU