Which type of secondary structure is characterized by coils and pleats?

The correct answer highlights the fact that both the alpha helix and the beta-pleated sheet are key forms of secondary structure found in proteins. The alpha helix is characterized by a right-handed spiral where the polypeptide chain coils every 3.6 amino acids, stabilized by hydrogen bonds between the backbone NH and CO groups. This structure is critical for providing flexibility and structural integrity to proteins.

On the other hand, the beta-pleated sheet is formed by pairs of strands that can be arranged either parallel or antiparallel to one another, creating a pleated appearance. These strands are also stabilized by hydrogen bonds, but in this case, between backbone chains in adjacent strands.

Both the alpha helix and beta-pleated sheet contribute to the overall 3D shape of proteins, with distinct functions based on their structure. Recognizing that they exhibit different types of structural motifs allows for a more comprehensive understanding of protein folding and stability. Therefore, the combination of both structures being characteristic of secondary structure is represented accurately in the selected answer.