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

Researchers cut a plasmid and a human insulin coding sequence with the same restriction enzyme and mix the fragments. Which enzyme finishes construction of the recombinant plasmid, and what does it do?

A.DNA ligase, which seals sugar phosphate backbones by forming phosphodiester bonds at each junction
B.Reverse transcriptase, which recopies the insert into a stable form
C.The same restriction enzyme again, trimming overhangs until they fit together
D.RNA polymerase, which transcribes across the junction to lock the insert in place

Explanation

Core Concept

In this restriction-enzyme cloning strategy, compatible DNA ends can base-pair but the sugar-phosphate backbones remain nicked. DNA ligase forms phosphodiester bonds that covalently seal the insert into the plasmid. This describes classical restriction-ligation cloning; recombinant DNA can also be assembled by other methods, so it is inaccurate to say every recombinant DNA construction ends with this exact ligation step.

Correct Answer

ADNA ligase, which seals sugar phosphate backbones by forming phosphodiester bonds at each junction

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