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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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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'.

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    $\begingroup$ In the SE post that OP mentions, the diagram is immediately preceded by a link to the source page of the diagram (via the word "schema"), and on that page there is a "Homework:" paragraph noting that the diagram is mislabeled. $\endgroup$
    – mgkrebbs
    Commented Jan 19, 2016 at 22:08
  • $\begingroup$ Oh, didn't see that! $\endgroup$
    – Aleksandr Hovhannisyan
    Commented Jan 19, 2016 at 22:35
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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.

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