Discussion
The glycosyl bond conformation in z-form of DNA is :
Answer: B
In Z-DNA the glycosyl bond is anti for pyrimidines and syn for purines.
Z-DNA is a left-handed double helix formed by alternating purine-pyrimidine sequences such as (CG)n, especially at high salt. Its repeating unit is a dinucleotide because the two kinds of nucleotide adopt different conformations: the pyrimidines (C) keep the usual anti conformation about the glycosyl bond, while the purines (G) flip to syn. This alternation gives the backbone its zigzag course, from which Z-DNA is named.
In B-DNA and A-DNA all bases are anti, so 'anti for both' describes the right-handed forms. The options with pyrimidines syn reverse the arrangement, and 'syn for both' occurs in neither form.
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