Which end of DNA bears the terminal phosphate group?

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Multiple Choice

Which end of DNA bears the terminal phosphate group?

Explanation:
DNA strands are defined by the groups at their ends. Synthesis proceeds by adding nucleotides to the 3' end, with the incoming nucleotide bringing its own 5' phosphate to form a phosphodiester bond with the 3' hydroxyl of the existing strand. This leaves the leftmost end carrying a free phosphate on the 5' carbon of the terminal nucleotide, while the rightmost end ends with a free 3' hydroxyl. So the terminal phosphate group sits at the 5' end. The 3' end has a hydroxyl, not a phosphate, and a 5' hydroxyl or a 3' phosphate end would not describe the usual ends of a DNA strand.

DNA strands are defined by the groups at their ends. Synthesis proceeds by adding nucleotides to the 3' end, with the incoming nucleotide bringing its own 5' phosphate to form a phosphodiester bond with the 3' hydroxyl of the existing strand. This leaves the leftmost end carrying a free phosphate on the 5' carbon of the terminal nucleotide, while the rightmost end ends with a free 3' hydroxyl. So the terminal phosphate group sits at the 5' end. The 3' end has a hydroxyl, not a phosphate, and a 5' hydroxyl or a 3' phosphate end would not describe the usual ends of a DNA strand.

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