major groove

ma·jor groove

in a detailed analysis of DNA structure, there are two types of grooves that can be seen; the major groove has the nitrogen and oxygen atoms of the base pairs pointing inward toward the helical axis, whereas in the minor groove, the nitrogen and oxygen atoms point outwards; important because the major groove is more dependent on base composition and may be the site for protein recognition of specific DNA sequences or regions.

major groove

A deep and wide furrow present in classic (Watson and Crick) DNA, which extends over the entire length of DNA, as long as the molecule remains in a normal or right-handed configuration; for the usual B-DNA, the major groove is 22-nm wide.