Question

Select the true statement.
All proteins have the same secondary structures.
A primary structure forms when a secondary structure folds into a shape.
The types of amino acids in a polypeptide determine the shape of its secondary structures.

Answer 1

The third statement is true: "The types of amino acids in a polypeptide determine the shape of its secondary structures."

Why:
- Different amino acids have different side-chain properties (size, charge, polarity, special residues like proline or glycine) that influence whether regions form α-helices, β-sheets, turns, or remain disordered.
- The first statement is false: proteins do not all have the same secondary structures (they vary).
- The second statement is false: primary structure is the amino-acid sequence; secondary structure is local folding (α-helices, β-sheets); tertiary structure is the overall 3D shape formed by folding.