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NEETZoologyMolecular Basis of Inheritance

During DNA replication, a replication fork exposes two template strands: Strand A with a polarity of 3^ 5^ and Strand B with a polarity of 5^ 3^ . Which of the following statements correctly identifies the strand that undergoes continuous synthesis and provides the correct reason?

Options

  1. ASynthesis is continuous on Strand B because DNA polymerase catalyses polymerisation in the 3^ 5^ direction.
  2. BSynthesis is continuous on Strand A because DNA polymerase catalyses polymerisation in the 3^ 5^ direction.
  3. CSynthesis is continuous on Strand B because DNA polymerase catalyses polymerisation in the 5^ 3^ direction.
  4. DSynthesis is continuous on Strand A because DNA polymerase catalyses polymerisation in the 5^ 3^ direction.

Correct answer

D. Synthesis is continuous on Strand A because DNA polymerase catalyses polymerisation in the 5^ 3^ direction.

Step-by-step solution

DNA-dependent DNA polymerase catalyses polymerisation only in one direction, that is 5^ 3^ . Consequently, on the template strand with 3^ 5^ polarity (Strand A), the synthesis of the new strand can proceed continuously in the 5^ 3^ direction. On the other template strand with 5^ 3^ polarity (Strand B), synthesis must occur discontinuously in small fragments (Okazaki fragments) because the enzyme can only add nucleotides in the 5^ 3^ direction. Answer: Synthesis is continuous on Strand A because DNA polymerase catal

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