Question

How many charged groups do all amino acid residues have at physiological pH?

1) 0
2) 1
3) 2
4) 3

Answer 1

At physiological pH, all amino acid residues generally have two charged groups — a basic amino group and an acidic carboxyl group, making option 3) 2 the correct answer.

Step-by-step explanation:

At physiological pH, which is approximately 7.4, all amino acid residues typically have two charged groups. These include the basic amino group (NH₃⁺) at the amino terminus and the acidic carboxyl group (COO⁻) at the carboxyl terminus. While the R group, or side chain, can influence the overall charge by being neutral, positively charged, or negatively charged, amino acids in their zwitterionic form will have these two charged groups. For instance, basic amino acids like Arginine (Arg), Lysine (Lys), and Histidine (His) have side chains that are positively charged under physiological conditions, while acidic amino acids will have negatively charged side chains. Nevertheless, the basic structure of amino acids gives them a minimum of two charged groups at physiological pH. Hence, the correct answer to the question is 3) 2.