Question
How does replication of the long DNA molecule occur? Explain the process.
OR
Explain the process of DNA replication with the help of a replicating fork.✓
Answer
- Replication of DNA.
- Replication of DNA occurs during S-phase of cell cycle.
- During replication of DNA, the two strands unwind upto a point and a replication fork is formed.
- Since the unwinding cannot take place for the entire length, replicaion starts from the replication fork.
- Both the strands act as templates for DNA synthesis.
- DNA polymerase is the enzyme that polymerises the bases/ nucleotides into a strand of DNA.
- Since this enzyme polymerises the nucleotides in 5' → 3' direction only, on one of the template strands (with 3' → 5' polarity), the new strand is synthesised as a continuous stretch (leading strand); it is called continuous synthesis.
- On the other template strand, (with 5' → 3' polarity), DNA strand is synthesised as short stretches (using primers), called Okazaki fragments; this is called discontinuous synthesis.
- Later, these short stretches are joined by DNA-ligase (lagging strand).
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