Which of the following amino acids will have a net positive charge at physiological pH?

Consider the side chains of each amino acid. Glutamine has a neutral amide group, aspartic acid has a carboxylic acid group, cysteine has a thiol group, and lysine has an amine group.

Determine the ionization state of each amino acid at physiological pH. Amino acids with acidic side chains (like aspartic acid) will be deprotonated and negatively charged, while those with basic side chains (like lysine) will be protonated and positively charged.