Answer 3
What are the major ways in which the structures of B-DNA and A-DNA differ from one another?

Although B-DNA and A-DNA both form right-handed double helices, the B-DNA helix has a larger pitch and hence a smaller width than that of A-DNA. In B-DNA, the helix axis passes through the base pairs and hence B-DNA has no internal spaces, whereas that of A-DNA has a 6 Angstrom diameter hole along its helical axis. The planes of the base pairs in B-DNA are nearly perpendicular to the helix axis, whereas in A-DNA, they are inclined from this direction by 20 degrees. As a consequence, B-DNA has a wide and deep major groove and a narrow and deep minor groove, whereas A-DNA has a narrow and deep major groove, but a wide and shallow minor groove.