Description of the two strands making up a double helix, which are arrayed in opposite directions in terms of 5' to 3' polarity.
Literally, and taking into account strand complementarity, the two stands of a double helix are arranged as:
5'-actgcatcaagccca-3'
3'-tgacgtagttcgggt-5'
The distinction between leading and lagging strands during DNA replication is a direct consequence of the antiparallel nature of DNA. That is, since DNA must be replicated in the 5' to 3' direction, each DNA strand must be replicated in opposite directions from each other: 3' faces one way (say, left) in one strand while 3' of the other strand faces the other way (here, right). As a consequence, only one of the two strands (the leading strand) can be replicated towards the replication fork whereas the other strand (lagging strand) must be replicated away from the replication fork.
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