This document presents information on the enzymes involved in DNA replication. It discusses six main enzymes - helicase, DNA polymerase, ligase, DNA topoisomerase I, DNA topoisomerase II, and telomerase. It provides details on the name, EC number, reaction catalyzed, and function of each enzyme. The conclusion states that DNA replication involves four classes of enzymes, including hydrolases, transferases, ligases and isomerases. It also notes a difference in ATP utilization between DNA topoisomerase I and II.

1. A PRESENTATION ON
ENZYMES INVOLVED IN DNA REPLICATION
Presented By :
Sunil Kumar Sahoo
Enrolment No-CUSB1703132020
First Semester, L.Sc.-503

2. CONTENTS –
INTRODUCTION
ENZYMES INVOLVED IN DNA REPLICATION
FUNCTION OF EACH ENZYME
CONCLUSION
REFERENCES

3. INTRODUCTION -
DNA is made up of two strands and the two strands of a parental
double helix of DNA are separated, the base sequences of each
parental strand serve as a template for the synthesis of new
complementary strand ,producing two identical progeny double
helices , called as DNA repliation.
It includes 3 processes like initiation ,elongation & termination.
DNA replication is a complex process involving numerous enzymes and
proteins.

4. ENZYMES INVOLVED IN DNA REPLICATION -
ENZYME NAME E.C NO CLASS OF ENZYME
HELICASE 3.6.4.12 HYDROLASE
DNA POLYMERASE 2.7.7.7 TRANSFERASE
LIGASE 6.5.1.1 LIGASE
DNA TOPOISOMERASE I 5.99.1.2 ISOMERASE
DNA TOPOISOMERASE II 5.99.1.3 ISOMERASE
TELOMERASE 2.7.7.49 TRANSFERASE
PRIMASE

5. 1. HELICASE -
E.C No – 3.6.4.12
EC 3– Hydrolases
EC 3.6– Acting on acid anhydrides
EC 3.6.4- Acting on ATP
EC 3.6.4.12- Dna helicase
REACTION : ATP +H2O = ADP+ Phosphate
SYSTEMATIC NAME : ATP phosphohydrolase
COMMENTS : DNA Helicases utilize the energy from ATP hydrolysis to
unwind double stranded DNA.

6. 2. DNA POLYMERASE -
E.C No – 2.7.7.7
EC 2 –Transferases
EC 2.7 –Transferring phosphorus containing groups
EC 2.7.7 –Nucleotidyltransferases
EC 2.7.7.7 –DNA-directed Dna polymerase
REACTION : 2’-deoxyribonucleoside 5’-triphosphate + DNAn = diphosphate +DNAn+1
OTHER NAMES - DNA polymerase ( I, II ,III ,α,ß ,ý )
SYSTEMATIC NAME – 2’-deoxyribonucleoside 5’-triphosphate : DNA
deoxynucleotidyltransferase (DNA –directed )
COMMENTS – Catalyses DNA -template –directed extension of the 3’- end of a DNA strand
by one nucleoide at a time.

7. 3. LIGASES -
E.C No - 6.5.1.1
Reaction: ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-
(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate
(overallreaction)

8. Continued..
SYSTEMATIC NAME: poly(deoxyribonucleotide)-3'-hydroxyl:5'phospho-
poly(deoxyribonucleotide) ligase (ATP)
COMMENTS: The enzyme catalyses the ligation of DNA strands with 3'-
hydroxyl and 5'-phosphate termini, forming a phosphodiester and
sealing certain types of single-strand breaks in duplex DNA.

9. 4.DNA TOPOISOMERASE I –
E.C No - 5.99.1.2
REACTION: ATP-independent breakage of single-stranded DNA, followed by
passage and rejoining.
SYSTEMATIC NAME: DNA topoisomerase
COMMENTS: These enzymes bring about the conversion of one topological
isomer of DNA into another, e.g., the relaxation of superhelical turns in
DNA, the interconversion of simple and knotted rings of single-stranded
DNA, and the intertwisting of single-stranded rings of complementary
sequences.

10. 5.DNA TOPOISOMERASE II –
E.C No - 5.99.1.3
REACTION: ATP-dependent breakage, passage and rejoining of double-
stranded DNA
ACCEPTED NAME: DNA topoisomerase (ATP-hydrolysing)
SYSTEMATIC NAME: DNA topoisomerase (ATP-hydrolysing)
COMMENTS: The enzyme can introduce negative superhelical turns into
double-stranded circular DNA. One unit has nicking-closing activity, and
another catalyses super-twisting and hydrolysis of ATP.

11. 6. TELOMERASE -
E.C No - 2.7.7.49
REACTION: a 2'-deoxyribonucleoside 5'-triphosphate + DNAn =
diphosphate + DNAn+1

12. Continued..
SYSTEMATIC NAME: 2'-deoxyribonucleoside-5'-
triphosphate:DNAdeoxynucleotidyltransferase (RNA-directed)
COMMENTS: Catalyses RNA-template-directed extension of the 3'- end
of a DNA strand by one deoxynucleotide at a time.

13. CONCLUSION -
Here 4 classes of enzymes ( Hydrolase, Transferase , Ligase , Isomerase
,Transferase ) are involved in DNA replication.
DNA Topoisomerase I & DNA Topoisomerase II belong to isomerase
group where DNA Topoisomerase I does not utilize ATP where as
DNA Topoisomerase II utilizes ATP.

14. REFERENCES -
Principle of Genetics ( Snustad & Simmons )
I.U.B.M.B
PDB (Protein Data Bank)