Definition of "antiparallel" []

• Of vectors, parallel but of opposite direction (adjective)
• Describing the orientations of the two strands of DNA (adjective)
• Describing two beta strands comprising a protein's secondary structure that are aligned and hydrogen bonded but the vector describing the amino- and carboxy-terminal ends of each strand are oriented 180° relative to one another. (adjective)
• A line that forms equal angles with two other lines, but in opposite directions. (noun)

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• "In most organisms, DNA is formed as a very long and very narrow double-helix formation of two DNA strands coiled around each other in a head-to-toe "antiparallel" orientation."
• "July 30, 2009 at 8:39 am the kittehs reminds me two electrons with all quantum numbers same except the spin parallel and antiparallel"
• "For example, noting that in Watson-Crick base pairing the paired bases have the same face-orientation in forming the antiparallel double helix tells us much of what we need to know to build the correct structure."