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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance3 Marks
Question
  1. Why does DNA replication occur in small replication forks and not in its entire length?
  2. Why is DNA replication continuous and discontinuous in a replication fork?
  3. Explain the importance of origin of replication' in a replication fork.
✓

Answer

  1. Replication of DNA occurs in small replication forks, because DNA is such a long molecule that the separation of the two strands along its entirelength requires a very high amount of energy.
  2. DNA polymerase can catalyse the polymerization of nucleotides only in 5' → 3' direction.
  1. So on the template strand with 3' → 5' polarity, DNA replication is continuous.
  2. On the template strand with 5' → 3' polarity, DNA synthesis occurs in short stretches as the opening of replication fork continues; later these short stretches are joined by the action of DNA ligases .
  1. Replication of DNA does not initiate randomly, and DNA polymerases on their own cannot initiate replication.
  1. So, there is a specific sequence on DNA, called origin of replication; DNA polymerase bindsto it and continues the process.

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