DNA replication occurs concurrently on the leading and lagging strands. The leading strand runs in the same direction as the replication fork and allows for continuous DNA synthesis. The lagging strand runs in the opposite direction and requires discontinuous DNA synthesis in fragments called Okazaki fragments. DNA polymerase III is the main polymerase in E. coli, consisting of a dimer core enzyme and accessory proteins that allow for high processivity of DNA synthesis on both strands concurrently.

1. CONCURRENTSYNTHESISONTHE
LEADING ANDLAGGINGSTRANDS

2. LEADINGAND LAGGING STRAND
The parent strand that runs 5’-3’ in the reverse direction of
fork movement is termed the leading strand ,and it serves as a
template for the continuous DNA synthesis.
The other parent strand that runs 5’-3’ in the direction of fork
movement is termed the lagging strand , and it serves as a
template for the discontinuous strand .

3. DNAPolymerase III
 It is a haloenzyme consist of a dimer containing 10 different
polypeptide unit.
This haloenzyme is main polymerase of E. coil.
It is made up of three assemblies :
• Clamp loading complex
• B sliding clamp processivity factor
• Core enzyme

4. Fig. showing the concurrent DNAsynthesis on the leading and the lagging strand

5. CONCLUSION
• Concurrent DNA may be achieved on both the leading and
lagging strand at a single replication fork .
• The lagging template strand is “looped” in order to invert
the physical direction of synthesis , but not the biochemical
direction.
• The enzyme functions as a dimer with each core enzyme
achieving synthesis on one or the other strand.

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