Question: Why is DNA structured in a double helix?

Judith Sleeman answered on 1 Feb 2019:

There are many reasons why the double helix is a good way to carry genetic information: the bases down the middle between the strands allow for a code to be carried (A, C, G, T assembled into three letter ‘words’); the code can be kept ‘safe’ inside the double helix; the two strands allow the code on the DNA to be replicated (copied) before cells divide; the helix can be wound up tightly to fit into the nucleus.

DNA is also a double helix because that’s how the particular sub-units of the structure (the sugar and phosphate of the backbone plus the bases) are able to link together at a chemical level.