iGen3 02-14

A, B and Z forms of DNA

The right-handed B form [middle] is the standard form in biological systems. The left-handed Z form [right] occurs occasionally in the middle of a B-form molecule. Bases are co-planar in both the B and Z forms. The right-handed A form [left] occurs in crystalline structures where the water concentration is reduced: the structure is distorted and the bases are no longer co-planar.

Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2010 by Steven M. Carr