DNA Structure and Replication

ID #2221

Why is double stranded DNA antiparallel? What are the advantages of that as opposed to just parallel?

You ask a good question. I think the main reason is stability. An antiparallel DNA double helix is more stable than a parallel double helix. If you tried to base pair a guanine with a cytosine with both bases facing up (as opposed to one right-side up and one upside down) they would be unable to hydrogen bond with one another. A parallel double helix would need entirely different nitrogenous bases to base pair stably. The polymerases that replicate DNA and transcribe RNA from DNA have evolved to read the template strand in the 3' to 5' direction to synthesize in the 5' to 3' directions. New enzymes would be needed to replicate a parallel double helix.

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