Explain why the double helix structure of DNA allows only a purine to pair with a pyrimidine?

3 Responses to “Explain why the double helix structure of DNA allows only a purine to pair with a pyrimidine?”

  1. emucompboy Says:

    When Crick eyeballed Franklin’s x-ray diffraction image of DNA, he noticed that the picture implied a constant width and regular repeating pattern for the molecule.
    Constant width, with base pairing, implies that a purine must pair with a pyrimidine, and never with another purine; similarly a pyrimidine can’t pair with another pyrimidine. These guys are different "widths."

  2. damnhippies50 Says:

    G to C has three hydrogen bonds, and A to T has two hydrogen bonds so they cannot mismatch

  3. tapoona Says:

    purines are A and G and pyrimidines are C and T. Just like the other answer said they pair up because of the number of bonds, but it doesn’t have to do with being a purine or pyrimidine. a good way to remember that A and G are purines is the pneumonic "Pure silver." Purines are A and G or Ag (silver).

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