Replication

AP Biology· difficulty 3/5

Linear chromosomes face an "end-replication problem": removal of the final RNA primer leaves a short 3' overhang that cannot be filled by DNA polymerase, shortening chromosome ends with each division.

Which enzyme adds repetitive sequences to compensate for chromosome shortening at telomeres?

A
$Ribonuclease H$
B
$DNA polymerase III$
C
$Topoisomerase II$
D
$Telomerase, a reverse transcriptase that uses an internal RNA template.$
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Explanation

Telomerase carries an internal RNA template and reverse-transcribes telomeric repeats onto chromosome ends, offsetting the shortening that results from removal of the final RNA primer.

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