Answers AFC AP Biology B2 DNA and RNA StructureQuestion 5

5

AssignmentMultiple Choice

DNA and RNA Structure

Question 5 • AFC AP Biology B2

Which statement best describes why DNA is built in the 5’ to 3’ direction?

Answer

A

A template strand is required for DNA polymerase to construct a complementary strand.

B

RNA primers are present where there is an available phosphate group on the nucleotide.

C

DNA polymerase acts on the OH group of the existing strand to add nucleotides.

D

The structure of DNA is symmetrical due to the location of sugar molecules in the strands.

Explanation

DNA polymerase adds each incoming nucleotide to the free 3′-OH group at the end of the growing strand. This extends the strand in the 5′ to 3′ direction, so choice C, “DNA polymerase acts on the OH group of the existing strand to add nucleotides,” is best. A template is needed to determine the sequence, but that does not explain the direction of synthesis.

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