Practice!

Sample Problem

Which of the following are correctly associated?

(A) primary protein structure—individual amino acids

(B) secondary protein structure—alpha helices

(C) tertiary protein structure—beta-pleated sheets

(D) quaternary protein structure—the completed protein complex

Solution

(B) and (D) are associated correctly. You may have been tempted to pick (A), but primary protein structure is the polypeptide chain, not the individual amino acids. Tertiary protein structure is the completed folding of the polypeptide, but not necessarily the completed protein (C), which may have multiple polypeptides. Beta-sheets are another secondary protein structure.