Advanced Placement (AP) Biology Practice Exam

Which type of bond would primarily stabilize protein tertiary structures?

1. Covalent disulfide bonds

2. Hydrogen bonds

3. Ionic bonds

4. Peptide bonds

The correct answer is: Covalent disulfide bonds

The bonds that primarily stabilize protein tertiary structures include covalent disulfide bonds. These bonds form between the sulfur atoms of cysteine residues in proteins and play a crucial role in the three-dimensional folding of polypeptide chains. The formation of disulfide bonds contributes to the stability and rigidity of the tertiary structure, as they create strong linkages that can help maintain particular folds against the influences of denaturing conditions. While hydrogen bonds, ionic bonds, and peptide bonds also play a role in the stability of protein structures, they do so in different ways. Hydrogen bonds are important for maintaining secondary structures like alpha helices and beta sheets, while ionic bonds contribute to favorable interactions between charged side chains in proteins. Peptide bonds, on the other hand, are the covalent bonds that link amino acids together in a polypeptide chain, establishing the primary structure of proteins but not specifically stabilizing tertiary structures. Thus, covalent disulfide bonds are particularly paramount in providing stability to the overall folded shape of proteins.