DNA replication is the process by which DNA copies itself to produce identical daughter molecules. Some key points: - The Meselson-Stahl experiment provided evidence that replication is semiconservative. - Replication begins at the origin and proceeds bidirectionally. DNA polymerase is the main enzyme that carries out replication. - Replication in eukaryotes involves multiple origins of replication, several DNA polymerases, and other proteins like PCNA and RFC. It also must coordinate with packaging DNA into chromatin and replication of mitochondrial DNA. - Differences between prokaryotic and eukaryotic replication include the number of replication forks, presence of histones, and size of Okazaki fragments.

1. DNA REPLICATION
RITTU CHANDEL
JR(MD BIOCHEMISTRY)
30-04-2013

2. REPLICATION
• A process in which DNA copies itself to produce
identical daughter molecules of DNA
• It is carried out with high fidelity

3. MESELSON AND STAHL EXPERIMENT
conclusion:
Semiconservative
replication

4. REPLICATION begins at origin;
proceeds bidirectionaly
1.Cairns experiment:
Both DNA strands replicate
simultaneously
2.Inman’s denaturation
technique

5. DNA synthesis is SEMIDISCONTINUOUS

6. DNA POLYMERASE
3 important properties
Bacteria- 5 polymerases
Dna polymerase1
3 ' - 5 ' and 5 ' - 3 ' exonuclease activity
5 ' - 3 ' endonuclease activity
Klenow fragment
When DNA
polymerase can
replicate DNA why
other enzymes
required?

8. REPLICATION- very accurate

11. DNA POLYMERASE 3(replicase)-main
replication enzyme

13. Comparisonoftwotypesofnick
sealingreactions

14. 1. initiation

16. • elongation
elongation

20. Final step in synthesis of lagging
strands

21. 3.termination

22. MEMBRANE BOUND REPLICATION

23. DNA replication IN EUKARYOTES
1. CELL CYCLE

24. 2. ORIGIN OF REPLICATION
Why many origin
of replication?
150 hrs in
comparison to 9
hrs

25. 3. EUKARYOTIC DNA POLYMERASE

26. • Eukaryotic enzymes
• PCNA
• RFC(replication factor C)
• MCM
• Prokaryotic counterparts
• Β sliding clamp
• Γ complex (clamp loader)
• helicases

27. 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

28. REPLICATION AT ENDS OF
CHROMOSOME

29. DIFFERENCE
• PROKARYOTIC REPLICATION
1. Initiation point specific(ori)
2. DNA poly-1,2,3,4,5
3. No mitochondria
4. Replication with only 1
replication fork
5. Theta structure observed
6. Only unwinding takes place
7. RNA as primer
8. Okazaki fragments are large
• EUKARYOTIC REPLICATION
1. Many ori
2. Many types-α, β, γ, δ, ε
3. γ DNA polymerase found in
mitochondria
4. Many replication forks
5. Theta structure not observed
6. Histone seperation as well as
unwinding
7. RNA/DNA as primer
8. Okazaki fragments are small

30. Inhibitors of DNA replication
• That affect either template or priming ability of
the growing strand
1. Intercalating agents-
anthracyclins(daunorubicin,doxorubicin)
2. Chain breakage-bleomycin
3. Interstrand crosslinks-mitomycin,nitrogen
mustard

31. • Act directly on polymerase or other enzymes
1. Acyclovir
2. DNA gyrase inhibitor-nalidixic acid
3. Topoisomerase 1 inhibitor- quinolone

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