Identify what is meant by secondary structure of proteins

The secondary structure of a protein refers to local folding patterns of the polypeptide chain, mainly:

• $\alpha$-helix
• $\beta$-pleated sheet

Recall what stabilises these structures

These secondary structures are stabilised by hydrogen bonds formed between:

• the carbonyl oxygen $({\rm C=O})$ of one peptide bond, and
• the amide hydrogen $({\rm N-H})$ of another peptide bond.

Check each option

A: Hydrogen bonding
Correct. Secondary structure is primarily stabilised by hydrogen bonds.

B: Glycosidic bond
Incorrect. Glycosidic bonds are found in carbohydrates, not responsible for protein secondary structure.

C: Peptide bond
Incorrect. Peptide bonds link amino acids to form the primary structure of proteins, but do not specifically stabilise secondary structure.

D: van der Waals forces
Incorrect. These may contribute to overall folding, especially tertiary interactions, but the main stabilising force for secondary structure is hydrogen bonding.

Final answer

The secondary structure of protein is stabilised by hydrogen bonding.