Which of the following structures includes beta-sheets and alpha-helices?

The structure that includes beta-sheets and alpha-helices is the secondary structure of proteins. Secondary structure refers to the local folding of the polypeptide chain into specific shapes stabilized by hydrogen bonding between the backbone atoms.

In alpha-helices, the polypeptide chain coils into a spiral shape, while in beta-sheets, strands of polypeptides lie alongside each other and are linked by hydrogen bonds, forming a sheet-like structure. These features are fundamental to the overall structure and function of proteins, contributing to their stability and the formation of the higher-order structures that follow. Thus, recognizing that beta-sheets and alpha-helices are key components of secondary structure is crucial for understanding protein architecture and function.