Query: What is the backbone of a DNA double helix made of?
Context: Two chains of DNA twist around each other to form a DNA double helix with the phosphate-sugar backbone spiralling around the outside, and the bases pointing inwards with adenine base pairing to thymine and guanine to cytosine. The specificity of base pairing occurs because adenine and thymine align form two hydrogen bonds, whereas cytosine and guanine form three hydrogen bonds.