Nucleic acids have a definite polarity, or directionality. Stated another way, one end of the molecule is different from the other end. How are these ends described?
A) One end has a hydroxyl group on the 2 carbon; the other end has a hydrogen atom on the 2 carbon.
B) One end contains a nitrogenous base; the other end lacks it.
C) One end has an unlinked 3' carbon; the other end has an unlinked 5 carbon.
D) One end has one phosphate group; the other end has two phosphate groups.

Question

Quizplus · Accepted Answer

Nucleic acids have a 5' phosphate group on one end and a 3' hydroxyl (-OH) group on the other end. This gives them a distinct polarity or directionality, as the nucleotides can only be added to the 3' end of the growing strand during DNA replication or transcription. Option A is incorrect because the hydroxyl group is actually on the 3' carbon, not the 2' carbon. Option B is partly correct but doesn't accurately describe the polarity of the molecule. Option D is incorrect because both ends have a phosphate group, but the difference is in the number of linked carbons between them (3' end has an unlinked carbon).

Nucleic Acids Have a Definite Polarity, or Directionality