DNA replication is the process by which DNA copies itself for cell division. It is semiconservative, meaning the parental double helix separates and each strand acts as a template for a new partner strand. Replication begins at an origin and proceeds bidirectionally. It occurs in 5'-3' direction and is semidiscontinuous on the lagging strand. High-fidelity replication depends on polymerase selectivity, proofreading, and mismatch repair. Helicases unwind DNA while topoisomerases relieve torsional strain. Single-stranded DNA binding proteins and DNA primase facilitate replication. DNA polymerase, ligase, and various repair proteins ensure accurate copying of the genome.

1. DNA
REPLICATION
Dr. Neethi R Krishnan

2. The process by which copying of base sequence
present in the parent strand to daughter strand,
thereby passing the genetic information from parent
to progeny

3. FUNDAMENTAL RULES OF
DNA REPLICATION

4. 1.DNA REPLI CATI ON I S
SEMI COSERVATI VE
This structure has no ve lfe ature s which are o f co nside rable bio lo g icalinte re st . . . It
has no t e scape d o ur no tice that the spe cific pairing we have po stulate d
im m e diate ly sug g e sts a po ssible co pying m e chanism fo r the g e ne tic m ate rial.
—Watson & Crick (1953)
lippincott's biochemistry 5th edition

5. REPLI CATI ON I S
SEMI COSERVATI VE
lippincott's biochemistry 5th edition

6. Nelson & Cox - Lehninger Principles of Biochemistry 5th
ed 977

7. 2. REPLI CATI ON BEGI NS AT AN
ORI GI N & USUALLY PROCEEDS
BI DI RECTI ONALLY
E.COLI ori C
BACTERIOPHAGE LAMBDA ori lambda
YEAST Autonomous replicating sequence
HUMANS Similar to yeast

9. REPLICATION FORKS
• The site where the pair of replicated segments come together
and join the non-replicated DNA.
• It’s a site where :
1)the parental double helix is undergoing strand separation.
2)nucleotides are being incorporated into the newly
synthesized Complementary strands

10. lippincott's biochemistry 5th edition

11. 3. REPLI CATI ON PROCEEDS I N 5’-3’
DI RECTI ON & I S
SEMI DI SCONTI NUOUS

12. 4.REPLI CATI ON HAS HI GH
FI DELI TY
• POLYMERASE SELECTIVITY
• PROOF-READING
• MISMATCH REPAIR

14. HELICASES
ATP-DRIVEN PROCESSIVE UNWINDING OF DNA

15. Cell and Molecular Biology - Concepts and Experiments (7th Ed);550

16. TOPOISOMERASES
• RELIEVES TORSIONAL STRAIN THAT
RESULTS FROM HELICASE-INDUCED
UNWINDING OF DNA
• NICKING RESEALING ENZYME

18. TWO FUNCTIONS :
1.Keep the two strands
of DNA separated in the
area of the replication
origin.
2.Protect the DNA from
nucleases that degrade
ssDNA.
SINGLE STRANDEDBINDING
PROTEIN (SSBP)

19. DNA POLYMERASES
• Enzyme that catalyse deoxyribonucleotide
polymerization
• Fundamental reaction is a phosphoryl group
transfer
• Central requirement:
A template strand
A primer

20. DNA POLYMERASES
3 IMPORTANT PROPERTIES
I. POLYMERISATION RATE
II. PROCESSIVITY
III. PROOFREADING

21. PROKARYOTIC DNA
POLYMERASE
Nelson & Cox - Lehninger Principles of Biochemistry 5th
ED;987

23. DNA POLYMERASE 1

26. DNA POLYMERASE III
Cell and Molecular Biology - Concepts and Experiments (7th Ed) ; 555

27. EUKARYOTIC DNA
POLYMERASE
lippincott's biochemistry 5th edition

28. DNA PRIMASE
• INITIATE THE SYNTHESIS OF RNA PRIMER
• DNA DEPENDENT RNA POLYMERASE(DNAG)
• LEADING STRAND : ONE PRIMER
SEQUENCE IS NEEDED
• LAGGING STRAND : CONTINUOUSLY
PRODUCED

29. DNA LIGASE
SEALS THE SINGLE STRANDED NICK BETWEEN
THE NASCENT CHAIN TO OKAZAKI FRAGMENTS
ON THE LAGGING STRANDS

37. I. LEADING STRAND SYNTHESIS
II. LAGGING STRAND SYNTHESIS
III. REMOVAL OF RNA PRIMER & GAP FILLING
IV.SEALING THE NICK

39. •The region where the two replication forks meet is defined as the “terminus
region” located roughly opposite of oriC.
•Bacteria use a “replication fork trap” system for successful termination of
replication and fork fusion. This requires two factors:
1) DNA terminator (Ter) sites
2) A specific terminator protein that can bind Ter (Tus protein in E.coli)

46. Jorrit M. Enserink; https://www.researchgate.net/

47. Jorrit M. Enserink; https://www.researchgate.net/

48. REPLICATION HAPPENS ONCE
IN EACH CELL CYCLE

51. TELOMERES
A telomere is a region of repetitive sequences at each
end of eukaryotic chromosomes; which protects the
end of the chromosome from deterioration or from
fusion with neighboring chromosomes.

52. While replicating DNA, the eukaryotic DNA
replication enzymes (the DNA polymerase protein
complex) cannot replicate the sequences present at
the ends of the chromosomes (or more precisely
the chromatid fibres). Hence, these sequences and
the information they carry may get lost. This is the
reason telomeres are so important in context of
successful cell division: They "cap" the end-
sequences and themselves get lost in the process of
DNA replication.

53. TELOMERASE
• Terminal transferase
• Ribonucleoprotein that adds a species-dependent
telomere repeat sequence to the 3' end of telomeres.
• reverse transcriptase enzyme that carries its
own RNA molecule which is used as a template
when it elongates telomeres

58. BASE EXCISION REPAIR

59. NUCLEOTIDE EXCISION
REPAIR

60. MISMATCH REPAIR

61. MISMATCH REPAIR

62. MISMATCH REPAIR
Guillotin, D., & Martin, S. A. (2014). Exploiting DNA mismatch repair deficiency as a
therapeutic strategy. Experimental Cell Research, 329(1), 110–115

63. PHOTOLYASE DNA DAMAGE

64. Ribezzo, F., Shiloh, Y., & Schumacher, B. (2016). Systemic DNA damage responses in
aging and diseases. Seminars in Cancer Biology, 37-38, 26–35.

67. REFERRANCES
• Biochemistry-stryer-5th-edition.
• Lippincott's biochemistry 5th edition
• Harpers illustrated biochemistry (29th edition)
• Nelson & Cox - Lehninger Principles of Biochemistry 5th
ED;
• Cell and Molecular Biology - Concepts and Experiments