DNA Structure and Replication · USMLE Step 1

What problem at the ends of linear eukaryotic chromosomes is addressed by the enzyme telomerase during replication?

  1. Accumulation of mismatched base pairs in the duplex
  2. Excessive supercoiling stress ahead of the fork
  3. Loss of terminal DNA after RNA primer removal
  4. Formation of stable hairpin loops at chromosome ends
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Correct answer: Loss of terminal DNA after RNA primer removal

Because removal of the RNA primer at the ends would leave a gap, telomerase extends the 3′ end of linear chromosomes, preventing progressive shortening (end-replication problem).

Difficulty: Medium Question 14 of 20

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