Final answer:
The three types of turnabouts discussed include β-turns, classic γ-turns, and inverse γ-turns, which contribute to the structure and function of peptides in proteins.
Step-by-step explanation:
The three types of turnabouts in the context of proteins are β-turns, classic γ-turns, and inverse γ-turns. A β-turn is a common structure in proteins that creates a sharp change in the peptide chain direction. The classic and inverse γ-turns span three amino acid residues and differ in the geometry of the side chains at the i+1 residue. The classic γ-turn, which is rare, generally leads to a reversal of the peptide backbone and forms antiparallel β-sheet structures. In contrast, the inverse γ-turn, which is more common, can introduce kinks in the backbone without necessarily reversing its direction. Understanding these turns and their mimetics can help in designing peptide-mimicking compounds.