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Eduncle posted an MCQ
December 30, 2019 • 15:46 pm 0 points
  • CSIR NET
  • Life Sciences

Following statements are being made about the orientation of the N-glycosidic bond between the base and the sugar in the following DNA duplexes.
(A)    'anti' for B form DNA duplexes
(B)    'syn' for B form DNA duplexes
(C)    'anti' for A form DNA duplexes
(D)    'syn' for A form DNA duplexes
Which one of the following combinations of the above statements is correct ?

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    Eduncle Best Answer

    The bases can exist in two distinct orientations about the N-glycosidic bond. These conformations are identified as, syn and anti. It is the anti conformation that predominates in naturally occurring nucleotides. i.e. in both B and A forms of DNA duplexes. There is only one known case where a purine adopts a syn conformation. The unusual form is to find in an even more unusual structure namely left handed Z-DNA.

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