Waaaaaay back in grade school we learned of the double-helix structure of DNA. Ever since then, I’ve seen DNA represented in popular media in one of two ways. Lacking the ability to post pics here, I’ll merely link to the Wikipedia page about Watson and Crick’s landmark 1953 paper that first described that structure. That page itself shows two different representations of DNA:

First, in Figure 2. We see the double-helix that I’ve always visualized. Imagine a stepladder. Define an axis right up its middle, and then twist the ladder about that axis. Each rung is always perpendicular to (and bisected by) the twist axis.

Second, in Figure 3. Imagine a stepladder. Lay it tangent to a cylinder whose diameter is maybe twice the width of the ladder. Set the ladder at some non-orthogonal angle so that when you wrap the ladder around the cylinder, it spirals up the cylinder’s length. The rungs (and legs) of the ladder lay flat against the surface of the cylinder.

Depending on which news program you’re watching, you might see one depiction or the other. So which one is correct?