Answer:
DNA is a double-stranded right-handed helix; the two strands are complementary because of complementary base pairing, and antiparallel because the two strands have opposite 5′−3′ orientation (Figure 1.1A). The diameter of the helical DNA molecule is 20 Å (=2 nm). ... The major grooves in DNA can bind proteins.
Step-by-step explanation:
smaller version
Many people perceive the double helical structure of DNA (left) to be an extremely elegant, and in some ways miraculous structure. Clearly, the presence of two complementary strands is an efficient solution to the problem of the replication of DNA - how to make two exact copies from one original - but why is DNA helical?
In fact, as this short tutorial aims to show you, the helix is a general response to the stacking up of single monomer units into a polymer - DNA can’t help being a helix.
This tutorial uses a utility called Jmol , which allows us to manipulate 3-D structures. If you click and drag on the DNA structure, you can rotate it around at will. Try it!
Helices are actually extremely common in macromolecules - the obvious example is the α-helix in proteins, but there are many others.