From which location on a DNA strand do exonucleases remove nucleotides?

From which location on a DNA strand do exonucleases remove nucleotides?

• A. Only the end of a chain
• B. Anywhere along the strand
• C. From the middle of the strand
• D. From the 5' end

Answer: (A)

Exonucleases act by trimming nucleotides one by one from an exposed end of a nucleic acid. They need a free terminus to begin removing units, so the action occurs at the ends of the strand rather than in the middle. Endonucleases, in contrast, cut within the strand. Some exonucleases remove from the 5' end and others from the 3' end, but in all cases the location is an end, not the interior. That’s why the best choice is that nucleotides are removed from the end of the chain.

Exonucleases act by trimming nucleotides one by one from an exposed end of a nucleic acid. They need a free terminus to begin removing units, so the action occurs at the ends of the strand rather than in the middle. Endonucleases, in contrast, cut within the strand. Some exonucleases remove from the 5' end and others from the 3' end, but in all cases the location is an end, not the interior. That’s why the best choice is that nucleotides are removed from the end of the chain.