Which of the following are the two main types of secondary structures in proteins?

The two main types of secondary structures in proteins are indeed alpha-helices and beta-sheets. These structures are stabilized by hydrogen bonds that form between the backbone atoms in the polypeptide chain, allowing the protein to achieve a more compact and organized form.

Alpha-helices are characterized by a right-handed coil where each turn of the helix contains approximately 3.6 amino acids. This helical structure contributes to the overall stability and function of many proteins. On the other hand, beta-sheets consist of strands that are connected laterally by two or more hydrogen bonds, forming a sheet-like structure. These arrangements can appear in parallel or antiparallel configurations and are also crucial for the stability of proteins.

Understanding these structures is essential as they play a significant role in determining the protein's overall conformation and biological functions, influencing aspects such as enzymatic activity and interaction with other molecules. Other options include terms that do not accurately describe the established classifications of protein secondary structures.