Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologymediummcq1 pt

At a replication fork, one new DNA strand grows continuously while the other forms short Okazaki fragments. Which feature explains this asymmetry?

A.Helicase cleaves one parental strand into pieces ahead of the replication machinery
B.Ligase can only seal nicks on the leading strand, leaving the lagging strand in pieces
C.Primase adds primers only to the leading template, forcing the other template to self-copy
D.Polymerase extends chains only from a free 3' end, so one template must be copied in short backward steps

Explanation

Core Concept

The two exposed templates run antiparallel, yet polymerase adds nucleotides only onto a growing 3' hydroxyl. On one template this geometry allows steady movement toward the fork. On the other, synthesis must restart repeatedly away from the fork, creating fragments that ligase later joins.

Correct Answer

DPolymerase extends chains only from a free 3' end, so one template must be copied in short backward steps

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