Final answer:
The DNA double helix can form two types of structures: the B-form and the Z-form.
Step-by-step explanation:
The DNA double helix can form two types of structures: the B-form and the Z-form.
The B-form is the most common form of DNA structure. It is right-handed and has a uniform diameter of approximately 2 nm throughout its length. The B-form is the stable, biologically active form of DNA.
The Z-form is a left-handed helical structure that occurs under certain conditions, such as high salt concentrations or particular DNA sequences. The Z-form is less common and has a zig-zag shape.