DNA REPLICATION IN PROKARYOTES INITIATION ELONGATION AND TERMINATION

1. KUVEMPU UNIVERSITY
SAHYADRI SCIENCE COLLEGE
SEMINAR TOPIC ON:
DNA Replication in prokaryotes
PRESENTED BY:
Anita P.D
1st Msc,
Dept of Biotechnology,
Sahyadri Science College,
Shivamogga.

2. CONTENTS
 Introduction
 History
 DNA Replication steps
 DNA Replication prokaryotes
 Role of enzymes in DNA replication
 Conclusion
 Reference

3. INTRODUCTION
 DNA replication is a biological process which produces two
identical daughter DNA strands from a double stranded parental
DNA.
 A basis for biological inheritance in all living organisms.
 This process is important in all known life forms and the general
mechanisms of DNA replication are not the same in prokaryotic
and eukaryotic organisms.
 Theoretically replication of double stranded DNA can be
conservative, dispersive or semi-conservative.

4. HISTORY
ARTHUR KORNBERG :-
 ArthurKornberg discovered DNA Polymerase.
 The Nobel prize in physiology or medicine 1959
was awarded jointly to Severo ochoa and Arthur
Kornberg for their discovery of the mechanisms in
the biological synthesis of ribonucleic acid and
deoxyribonucleic acid.
 Meselson and Stahl:- During the DNA replication
process we didn’t know about semi-conservative
method , so some of the scientists assumed that, the
DNA cell are totally newly synthesized , but some other
scientists said that due to huge content of DNA in a cell
of an organisms the fragmentation takes place to
replicate the cells, but from another hypothesis its
considered as semi-conservative method.

5. DNA Replication steps
The important steps involved in DNA replication.
 Initiation
 Elongation
 Termination
1. Initiation:- DNA replication demands a high degree of accuracy
because even minute mistake would result in mutations.
 Thus, replication cannot initiate randomly at any point in DNA.
 For the replication to begin there is a particular region called the
origin of replication.

6. 2.Elongation :-
 As the strands are separated , the polymerase enzymes start synthesising the
complementary sequence in each of the strands.
 The parental strands will act as a template for newly synthesising daughter strands.
 It is to be noted that elongation is unidirectional that is DNA is always polymerised
only in the 5’to 3’ direction.
 They occur as fragments called Okazaki fragments .

7. 3.Termination:- Termination of replication occurs in different ways in
different organisms. In E.coli like organisms, chromosomes are circular.
And this happens when the two replication forks between the two
terminals meet each other.

8. Role of enzymes in DNA replication
Enzyme/protein Specific function
DNA Polymerase I Removes RNA primer and replaces it with newly synthesized DNA
DNA Polymerase II Repair enzyme with 3`to 5` exonuclease activity.
DNA Polymerase III Main enzyme that adds nucleotides in the 5’-3’ direction.
Helicase Opens the DNA helix by breaking hydrogen bonds between the nitrogeneous bases
Ligase Seals the gaps between the Okazaki fragments to create one continuous DNA
strand
Primase Synthesis RNA primers needed to start replication
Sliding clamp Helps to hold the DNA Polymerase is place when nucleotides are being added
Topoisomerase Helps relieve the strain on DNA when unwinding by causing breaks, and then
resealing the DNA
Single-Strand binding proteins
(SSB)
Binds to single-stranded DNA to prevent DNA from rewinding back.

9. DNA Replication prokaryotes
 DNA unwinds at the origin of replication.
 Helicase opens up the DNA-forming replication forks; these are extended
bidirectionally
 Single-strand binding proteins coat the DNA around the replication fork to
prevent rewinding of the DNA
 Topoisomerase binds at the region ahead of the replication fork to prevent
supercoiling.
 Primase synthesizes RNA primers complementary to the DNA strand.
 DNA polymerase III starts adding nucleotides to the 3’-OH end of the primer.
 Elongation of both the lagging and the leading strand continues
 RNA Primers are removed by exonuclease activity

10. Gaps are filled by DNA Polymerase I by adding dNTPs.
The gap between the two DNA fragments is sealed by DNA ligase, which helps
in the formation of phosphodiester bonds.
DNA gyrase (reduces supercoiling which builds up during DNA unwinding)
The leading and lagging strands continue to elongate.

11. CONCLUSION
DNA replication is essential for the survival of all living organisms.
Prokaryotic replication begins with the unwinding of DNA at the site of
origin of replication.
Prokaryotes are single-celled organisms that lack a nucleus.

12. REFERENCES
Textbook of CELL and MOLECULAR BIOLOGY, Ajoy Paul, 4th edition Books and
Allied (p) Ltd.
BIOCHEMISTRY BOOK, Dr U Satyanarayana and Dr U Chakrapani, 4th edition.