Final answer:
The traditional DNA double helix forms B-DNA, with a right-handed spiral, while the alternate form, Z-DNA, has a zig-zag appearance and is a left-handed helix.
Step-by-step explanation:
The traditional DNA double helix is a right-handed helix that forms B-DNA; another competing form is Z-DNA, which is known for its zig-zag appearance and being a left-handed helix.
DNA is known to adopt various structural forms. The most familiar form, often depicted in textbooks, is B-DNA, identifiable by its right-handed spiral structure. This form of DNA is stabilized by the hydrogen bonding between complementary bases, notably adenine with thymine and cytosine with guanine, which resemble steps of a spiral staircase.
On the other hand, Z-DNA is a less common form that takes on a left-handed helical shape and displays a characteristic zig-zag pattern. The existence of Z-DNA suggests the flexibility of DNA molecules and its ability to exist in different conformations based on the chemical and physical conditions.