What structural feature is primarily responsible for the tertiary structure of proteins?

The tertiary structure of proteins is determined by a variety of interactions between the amino acid side chains that contribute to the overall three-dimensional shape of the protein. Primarily, hydrogen bonding, hydrophobic interactions, salt bridges, and disulfide bonds all play significant roles in stabilizing this structure.

Hydrogen bonds occur between polar side chains, helping to stabilize the folding of the protein. Disulfide bonds, which form between cysteine residues, are covalent links that provide additional structural integrity. Salt bridges, or ionic interactions, arise from the attraction of oppositely charged side chains. Hydrophobic interactions occur when nonpolar side chains cluster together to avoid contact with water, further driving the protein into a specific shape.

Considering all these interactions combined, the correct response acknowledges that both sets of structural features—hydrogen bonding and disulfide bonds, as well as salt bridges and hydrophobic interactions—are essential for maintaining the tertiary structure. This comprehensive view explains why the correct choice encompasses both sets of interactions, as they collectively contribute to the protein's stability and functionality.