What is a beta turn?

A beta turn is characterized as a specific structural element in proteins that allows the peptide chain to make a sharp turn or bend, enabling it to reverse direction. This structural feature typically involves a segment of four amino acid residues, allowing the polypeptide chain to pivot approximately 180 degrees. The tightness of this turn is facilitated by hydrogen bonds, often between the first and fourth residues of the turn, which helps stabilize the structure and allows for compact folding of the protein.

Understanding the significance of beta turns is crucial since they play a key role in the overall folding and stability of proteins, particularly in regions where the polypeptide backbone needs to change direction sharply. This is essential for creating functional protein domains and for maximizing the variety of structures that proteins can adopt. Other choices describe distinct structural elements in proteins but do not accurately capture the essence of what a beta turn is.