DNA and RNA Polymerases Can Only Synthesize in the ________

Question

DNA and RNA polymerases can only synthesize in the ________ direction.
A) forward
B) 3'-to-5'
C) 5'-to-3'
D) reverse
E) 5'-to-3' or 3'-to-5'

Accepted Answer

Both DNA and RNA polymerases can only synthesize in the 5'-to-3' direction, meaning they add nucleotides to the 3' end of the growing strand. This is due to the chemistry of the reaction, which requires the hydroxyl (-OH) group on the 3' carbon of the sugar to be available for the formation of the phosphodiester bond between nucleotides. Therefore, choices A, B, and D are incorrect as they do not describe the directionality of polymerase synthesis, and choice E is not specific enough as it includes both directions.