Final answer:
The sides of the DNA molecule consist of alternating phosphate and sugar groups, forming a backbone that is antiparallel, allowing for base pairs of adenine with thymine and cytosine with guanine to link the two DNA strands together into a double helix.
Step-by-step explanation:
The sides of a DNA molecule, also known as the backbone, are made up of alternating phosphate and sugar (deoxyribose) groups. These chains are known to be antiparallel in orientation, meaning that they run in opposite directions; one strand's 5' end aligns with the other strand's 3' end. This structure allows for the formation of the DNA double helix, resembling a twisted ladder. The steps of this ladder, or the base pairs, are formed by the nitrogenous bases adenine (A), thymine (T), cytosine (C), and guanine (G). Adenine pairs with thymine, forming two hydrogen bonds, and cytosine pairs with guanine, forming three hydrogen bonds, which hold the two strands together.