Final answer:
The overall charge on a protein is largely affected by the pH and the ionizable groups present in the amino acid side chains. The environment's pH can cause these groups to gain or lose protons, altering the protein's net charge.
Step-by-step explanation:
The overall charge on a protein is affected by a variety of factors, and the correct answer from the options provided is c) pH and ionizable groups. The pH of the environment can affect the ionization state of the amino acid side chains, thereby altering the charge of the protein. Proteins have ionizable groups, especially on their side chains, which can gain or lose protons depending on the pH, leading to changes in the net charge of the protein.
Other interactions mentioned, such as hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide linkages, are primarily responsible for determining a protein's tertiary structure. These interactions stabilize the protein's structure but do not directly impact the overall charge as much as pH and ionizable groups do.