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In this video on DNA replication, the diagram shows the unwound DNA as still being anti-parallel, but the first diagram in this post on Biology SE shows that the individual strands are 5'____5' and 3'_____3'. So my question is the following:

Does a single, unwound strand of DNA run as either 5'______3' or 3'_______5', or does it run either 5'______5' or 3'________3'?

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Aleksandr Hovhannisyan
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A single, unwound strand of DNA runs 5' to 3', the video is correct. When wound properly, the strands run in reverse directions, 5' to 3' for the first, 3' to 5' for the other. That diagram is not helpful, though the post itself is quite good.

Jared Andrews
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DNA strands always have one 3' end and one 5' end (since each nucleotide has one of each and a strand is formed by connecting the 3' side of one nucleotide to the 5' side of another nucleotide). In a double helix DNA molecule, the two strands run in opposite directions.

The Pearson Education diagram in the post you referenced has one pair of the strand ends mislabelled. The lefthand-most labels 5' above the 3' should have been 3' above 5'.

mgkrebbs
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