oxygen affinity. 1. The structure of hemoglobin is the basis for its A. tertiary; extremely high B. tertiary; adjustable C. quaternary; extremely high D. quaternary; adjustable 2. Which of the following is true for the ligand binding sites of all ligand-binding proteins? A. They are rigid and inflexible. B. They are only composed of amino acid side chains. C. They are structurally and chemically complementary to the ligand. D. They are occupied by prosthetic groups. 3. What protein structural feature is most prevalent in myoglobin and hemoglobin? A. disulfide bonds B. B-sheets C. B-turns D. a-helices