The secondary structure of protein is stabilised by:

Solution

Chemistry ma’am · 3 steps

Ask which bond holds the helix and the sheet in shape: it is the N–H to C=O hydrogen bond.

1. Primary structure. The primary structure is the sequence of amino acids, joined by peptide bonds (-CO-NH⁻). These covalent bonds make the chain itself, not its folded shape.
2. Secondary structure. The secondary structure is the regular shape the chain takes: the α-helix or the β-pleated sheet. Each shape is held by hydrogen bonds between the >C=O of one peptide group and the -NH of another.

   Bond or force	Where it acts	Role
   Hydrogen bonding	C=O and N-H of backbone peptide groups	holds the α-helix and β-sheet
   Glycosidic bond	between sugar units	links monosaccharides, not found in proteins
   Peptide bond	between amino acids	builds the primary structure
   van der Waals forces	between side chains	helps the tertiary folding

3. So. The secondary structure of a protein is stabilised by hydrogen bonding, option (a).

The idea to keep. Match each level of protein structure to its bond: peptide bonds give the primary level, H-bonds the secondary, and side-chain forces (H-bonds, disulphide, ionic, van der Waals) the tertiary.

Answer from the NTA final answer key. Solution by PrepWiser.