Final answer:
B-turns are sequences of four amino acid residues that cause a reversal of the peptide backbone, while y-turns are another type of turn found in proteins that form a seven-membered ring shape. To determine if an organic scaffold mimics a turn, its geometry can be compared to experimental turn structures found in proteins.
Step-by-step explanation:
A B-turn is a sequence of four amino acid residues in a protein that causes a reversal of the peptide backbone. It is characterized by specific values of the backbone torsion angles of the residues. The most common types of B-turns are types I, I, II, II', and VIII. These turns can be stabilized by a CO-NH₁3 hydrogen bond.
The y-turn is another type of turn found in proteins. It spans over three amino acid residues and forms a seven-membered ring shape. There are two types of y-turns: the classic y-turn and the inverse y-turn. The classic y-turn causes reversal of the backbone direction and is mainly found in ß-hairpin structures, while the inverse y-turn is more common and does not cause reversal of the backbone direction.
When it comes to mimicking these turns, one way to characterize a potential turn mimicking moiety is to compare its geometry with experimental turn structures found in proteins. This can be done by comparing relevant parts of the potential mimetic to a determined 3D structure of a turn. By comparing the distances, angles, and directions, it is possible to determine if a particular organic scaffold mimics a turn and which specific class of turn it belongs to.