The document summarizes DNA replication in prokaryotes. It describes how DNA replication begins at the origin of replication and proceeds bidirectionally. DNA helicases unwind and separate the DNA strands, while DNA polymerase adds nucleotides to the leading strand continuously and the lagging strand discontinuously in Okazaki fragments. DNA polymerase proofreads the newly synthesized strands as replication occurs. DNA ligase and DNA polymerase I then join the Okazaki fragments.

1. Central Dogma of Molecular
Biology
DNA Replication and
General Chracteristics
DNA Replication and
Proofreading in Prokaryotes

2.  The central dogma of molecular biology
describes the flow of genetic information in
cells from DNA to messenger RNA (mRNA) to
protein.

3.  It occurs in all Living Organisms.
 It is non-specific. It means that once DNA
replication begins, it will not stop (normally)
until all the DNA is replicated.
 It is semi-conservative.
 It is bidirectional.
 DNA polymerases read the template strand
from 3’ 5’ and synthesize the new
DNA strand from 5’ 3’.

4.  Initiation
DNA A box and DNA A Proteins
Formation of Replication Bubble and Replication Fork
SSB
Helicases
 Supercoiling and Topoisomerases
 Elongation
Elongation of Leading Strand
ProofReading
Okazaki fragments and Lagging Strand
DNA pol I and Ligases
 Termination

5.  DNA replication begins at a single,unique AT-
rich sequence site called “Origin of
Replication” or “Ori”.
 As the two strands unwind and separate ,
synthesis occurs bidirectionally generating a
replication bubble.
 Initiation of DNA replication requires a group
of proteins collectively called “Pre-Priming
Complex”.

7.  DnaA proteins binds to DnaA Boxes within origin
of replication , causing the short AT-rich regions
in the origin to melt.Melting is ATP dependent ,
and results in strand separation with the
formation of localized regions of ssDNA.
 Helicases bind to ssDNA near the replication fork
and then move into the neighboring double-
stranded region, forcing the strands apart.Energy
is provided by ATP.
 Unwinding causes the problem of supercoiling in
other regions of DNA molecule that is solved by
Topoisomerases.

8.  SSB proteins bind to
ssDNA generated
by helicases. They
keep the two
strands of DNA
separated and also
protect DNA from
Nucleases.
 Binding of SSB
proteins is Co-
operative.

9.  The strand that is being copied in the
direction of the advancing replication fork is
called the Leading strand and is synthesized
continuously.
 The strand that is being copied in the
direction away from replication fork is
synthesized discontinously ( okazaki
fragments) is called the Lagging Strand.

11.  Primase synthesizes the short stretches of
RNA that are complementary and antiparallel
to the DNA template. These are called Primer
sequence.
 Only one Primer sequence is required at the
Leading strand whereas primer sequences are
synthesized constantly at Lagging strand.

13.  After the synthesis of Primer , DNA Pol III
begins to add nucleotides along the single
stranded template.
 At the leading strand, nucleotides are being
added continously.
 At the lagging strand, DNA pol III adds the
nucleotides until it reaches the next primer
sequence. It then deattaches , and bind again
at the next primer sequence , causing it’s
elongation and formation of Okazaki
fragments.

15.  DNA pol III while synthesizing the new DNA
strands also Proofreads them by it’s 3’ 5’
exonuclease activity.
 It is highly important for the survival of an
organism that the nucleotide sequence of
DNA be replicated with as few errors as
possible.

17.  DNA pol I with it’s 5’ 3’ exonuclease
activity removes the primer sequences and
replaces them with DNA .
 The final phosphodiester linkage between the
DNA chain synthesized by DNA pol III and the
chain made by DNA pol I is joined by DNA
ligases.

19.  Termination in E.Coli is mediated by binding
of the protein “Tus (terminal utilization
substance)” to termination sites on the DNA ,
stopping the movement of DNA polymerase.