Download - DNA Replication
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DNA REPLICATION
RITTU CHANDELJR(MD BIOCHEMISTRY)30-04-2013
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REPLICATION
•A process in which DNA copies itself to produce identical daughter molecules of DNA
•It is carried out with high fidelity
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MESELSON AND STAHL EXPERIMENT
conclusion:
Semiconservative replication
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REPLICATION begins at origin; proceeds bidirectionaly
1.Cairns experiment:Both DNA strands replicate simultaneously
2.Inman’s denaturation technique
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DNA synthesis is SEMIDISCONTINUOUS
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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?
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REPLICATION- very accurate
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DNA POLYMERASE 3(replicase)-main replication enzyme
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Com
pari
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ypes
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seali
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react
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s
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1. initiation
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•elongation
elo
ng
ati
on
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Final step in synthesis of lagging strands
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3.termination
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MEMBRANE BOUND REPLICATION
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DNA replication IN EUKARYOTES1. CELL CYCLE
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2. ORIGIN OF REPLICATION
Why many origin of
replication?
150 hrs in comparison to
9 hrs
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3. EUKARYOTIC DNA POLYMERASE
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• Eukaryotic enzymes• PCNA• RFC(replication factor C)• MCM
• Prokaryotic counterparts• Β sliding clamp• Γ complex (clamp loader)• helicases
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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
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REPLICATION AT ENDS OF CHROMOSOME
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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
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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
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•Act directly on polymerase or other enzymes
1. Acyclovir2. DNA gyrase inhibitor-nalidixic acid3. Topoisomerase 1 inhibitor- quinolone
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BIBLIOGRAPHY•SATYANARYAN•VASUDEVAN•RANA SHINDE•LIPPINCOTT•HARPER•LEHNINGER•BHAGVAN•MARKS•VOET THANK YOU