INTRODUCTION E. Coli: As a study model, Stages of DNA replication, process of each step with diagram

1. DNA REPLICATION in E.coli
Presented by :
Khushbu’s Microbiology

2. INTRODUCTION
DNA replication : biological process of producing
two identical replicas of DNA from one original
DNA molecule
.DNA replication occurs : all living organisms
acting as the most essential part for
biological inheritance

3. DEFINATION:
→ Cellular metabolic process
→ Cell duplicates one or
more molecules of DNA.
→ DNA replication begins :
specific sequences,
known as origins of
replication, are recognized
and bound by initiation
proteins

4. E. Coli :As a Study Model
 Small size of the genome
 Mutants that are available.
 E. Coli : 4.6 million base pairs (mbp)
in a single circular chromosome
 Replicated in approximately 42 minutes,
starting from a single origin of replication and
proceeding around the circle bidirectionally
e.g : in both directions.
 Approximately 1000 nucleotides are added per
second.

5. Basic Steps of DNA Replication
 E.Coli DNA replication process :called “Ori.C”
 The synthesis of a DNA Replication process : can
be divided into
THREE stages
1) Initiation
2) Elongation
3) Termination

6. Initiation Stage

7. Elongation Stage
 DNA polymerases are responsible creating the
new strand by a process called elongation.
 There are five different known types of DNA
polymerases in bacteria .E. coli, polymerase III is
the main replication enzyme, while polymerase I,
II, IV and V are responsible for error checking and
repair.
 DNA polymerase III binds to the strand at the site
of the primer and begins adding new base pairs
complementary to the strand during replication.
 The lagging strand begins replication by binding
with multiple primers. Each primer is only several
bases apart. DNA polymerase then adds pieces of
DNA, called Okazaki fragments, to the strand
between primers.
 This process of replication is discontinuous as the
newly created fragments are disjointed.

8. Termination Stage
• Termination sequences : two replication forks to pass through
in only one direction
• Topoisomerase 2 in E. coli unlinks or decatenates the two
circular DNA duplexes by breaking the phosphodiester bonds
present in two successive nucleotides of either parent DNA or
newly formed DNA & thereafter the ligating activity ligates
that broken DNA strand and so the two DNA get formed.

9. THANKS