Q. A doctor is giving a lecture on the fundamental building blocks of life - amino acids. She explains to her medical students that amino acids, as the name suggests, contain both an amino group and a carboxyl group, and she explains how the different side chains (R-groups) impart unique properties to the 20 standard amino acids found in proteins. She highlights that these R-groups can make an amino acid polar or nonpolar, acidic, or basic. She tells her students that basic amino acids possess an R-group with a positive charge at physiological pH, which is primarily due to the presence of extra amino groups. She quizzes her students, asking, "Which of the following amino acids is an example of a basic amino acid?"