Question

"Which factor is most important in determining a protein's optimum pH?

A. The sensitivity of hydrocarbon side chains to pH.
B. The number of amino groups in the protein's backbone.
C. The locations of side-chain carboxyl groups.
D. The number of backbone carboxyl groups.
E. The pH of the protein's environment."

Answer 1

The most important factor in determining a protein's optimum pH is the locations of side-chain carboxyl groups, as the ionizable side chains greatly influence protein structure and function.

Step-by-step explanation:

The factor most important in determining a protein's optimum pH is the pH sensitivity of the amino acids that make up the protein's structure, particularly the side chains. Specifically, the locations of side-chain carboxyl groups (C) are most important. This is because the side chains can be acidic, basic, polar, or nonpolar, and their ionization states are affected by pH, which in turn affects the protein's structure and function. Acidic side chains, such as those with carboxylic acid (-COOH), ionize to carboxylate anions (-COO-) under physiological conditions. Basic side chains, which may contain amine groups, become charged at different pH values. Therefore, the nature of these side chains and their ionizable groups define how the protein interacts with the environment and determine its optimum pH.