AAMC FL Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice identifies hydrogen bonds as the type of bond that links DNA bases together. In the structure of DNA, the bases adenine (A), thymine (T), cytosine (C), and guanine (G) pair specifically with one another: adenine forms two hydrogen bonds with thymine, while cytosine forms three hydrogen bonds with guanine. These hydrogen bonds are critical for maintaining the integrity of the DNA double helix, allowing the strands to hold together while still permitting the strands to separate during processes like replication and transcription.

Other types of bonds mentioned, such as covalent bonds, specifically connect the phosphate group of one nucleotide to the sugar of another nucleotide, forming the backbone of the DNA strand. Ionic bonds generally involve the attraction between charged particles and do not play a role in base pairing. Disulfide bonds are covalent links that form between cysteine residues in proteins, contributing to the protein's three-dimensional structure, but they do not pertain to the pairing of DNA bases.