Which of the following can stabilize tertiary structures of proteins?

Stabilization of tertiary structures in proteins is achieved through a variety of interactions, all of which play significant roles.

Ionic bonds, which occur between positively and negatively charged side chains, provide strong interactions that can effectively stabilize the overall structure of the protein. These ionic interactions are particularly important in maintaining the folded state under physiological conditions.

Van der Waals forces are weak attractions that occur between all atoms due to transient dipoles. Although individually weak, these forces can collectively contribute to the stability of the protein structure, especially when there are many atoms participating in these interactions within the closely packed interior of a protein.

Disulfide bonds, which are covalent linkages formed between the thiol groups of cysteine residues, offer significant stabilization for tertiary structures. They create a strong bond that can lock parts of the protein together, thereby maintaining its overall shape against denaturing forces.

Since all these interactions—ionic bonds, van der Waals forces, and disulfide bonds—contribute to stabilizing the tertiary structure, selecting "all of the above" acknowledges the importance of each type of bond in supporting protein conformation and functionality.