[Campbell Biology P.378] According to Figure 16.21 and the accompanying text, which of the f... | Practice Question

According to Figure 16.21 and the accompanying text, which of the following is the primary reason for the shortening of linear DNA molecules with each round of replication?

  • A: The leading strand cannot be fully replicated to its 3' end.
  • B: RNA primers are removed from the 5' end of new lagging strands, and there is no 3' end for DNA polymerase to extend.
  • C: DNA polymerase I is unable to synthesize DNA in the 5' to 3' direction.
  • D: DNA ligase fails to join the last Okazaki fragment to the rest of the lagging strand.

Explanation

Linear DNA molecules shorten with each replication because DNA polymerase cannot synthesize DNA without a pre-existing 3' hydroxyl group to add nucleotides. On the lagging strand, after the final RNA primer is removed from the 5' end of the newly synthesized strand, there is no adjacent 3' end available for DNA polymerase to fill this gap, leading to progressive shortening.