Final answer:
Beta-pleated sheets are characterized by folds stabilized by hydrogen bonds between amino groups and carboxyl groups. They are also characterized by interactions between the R groups of amino acids. The correct option is (e).
Step-by-step explanation:
Beta-pleated sheets are characterized by folds stabilized by hydrogen bonds between amino groups and carboxyl groups, as well as by interactions between the R groups of amino acids. These hydrogen bonds form between the partially positive nitrogen atom in the amino group and the partially negative oxygen atom in the carboxyl group of the peptide backbone. The R groups are attached to the carbons in the backbone and extend above and below the folds of the pleat.
The pleated segments of beta-pleated sheets align parallel or antiparallel to each other, creating a sheet-like structure. Additionally, beta-pleated sheets can also be stabilized by other types of bonds, such as ionic bonds, disulfide bridges, hydrophobic interactions, and more hydrogen bonds.
This means that the correct answer to the question is e. both a and d are correct, as beta-pleated sheets are characterized by both the interactions between the R groups of amino acids and the various bonds that stabilize their structure.