Prokaryotic DNA replication begins at the origin of replication site where the replication fork is formed. DnaA and other proteins recognize the origin site and unwind the DNA double helix. RNA primers are synthesized which allows DNA polymerase III to begin bidirectional DNA synthesis of the leading and lagging strands. Okazaki fragments are formed and ligated on the lagging strand. Replication terminates when the replication forks meet at the termination site and the daughter chromosomes are separated.

1. Prokaryotic DNA replication
1

2. Prokaryotic organisms duplicate its genomic DNA, synthesizing a new copy which it passes on
to daughter cells.
 The process of replication starts from origin of replication site (ori site) and proceeds in two
direction.
 This bidirectional replication process of prokaryotes is called Theta (θ) mode of replication.
 Multiple accessory proteins and enzymes are essential for the replication process.
2

3. protein function
Dna A Recognises ori sequence
Dna B (DNA helicase) Unwinds DNA double helix
Dna C Assists in ori sequence recognition
DNA polymerase DNA strand synthesis
DNA primase RNA Primer synthesis
SSB Binds with single stranded DNA
DNA gyrase Topological strain reduction
3

4. The process of replication is carried on in 3 steps -
1. Initiation,
2. Elongation,
3. Termination.
Initiation
1. Replication fork is formed when DnaA recognises ori site. DnaB then binds with 13-mer
repeats and with DnaC. This complex opens the local AT rich region, where with the help
of DNA gyrase, strands are separated and stabilized.
2. The RNA primer is then synthesized by primase which provides free 3’-OH group for
DNA elongation.
3. With the help of synthesized primer, DNA polymerase III starts the process of replication
at the replication fork. As DNA polymerase enzyme cannot synthesize a strand on its own,
primer is an absolute requirement.
4

5. Elongation
1. This step synthesizes both strand (leading & lagging) simultaneously.
2. The dNTPs are connected continuously to the primer or to the nascent DNA chain by enzyme
DNA polymerase III in 5’ to 3’ direction.
3. Synthesis of both strand is done by DNA polymerase III. The leading strand is synthesized
continuously while the lagging strand is synthesized in short sequence chains called okazaki
fragments.
4. Nicks and fragments are connected with the help of ligase and DNA polymerase I.
5

6. Termination
1. As prokaryotic replication is bidirectional, the two replication forks meet at the opposite
end of the ori site. This point is called ter.
2. A special protein called Tus protein allows the two interlinked ring to pass through each
other, only in one direction.
3. Primers are removed and Topoisomerase 2 unlinks the two circular DNA duplexes by
phosphodiester bond breakage.
6

7. Thank you.
7