Which structure of proteins gives rise to fibrous and globular proteins?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Tertiary Structure
Proteins are described at four levels of structure. The tertiary structure gives the protein its shape as a whole, fibrous or globular. It is held by hydrogen bonds, disulphide linkages, van der Waals and electrostatic forces.
Why the other options are incorrect
Option (1) Primary Structure — Incorrect. This is only the sequence of amino acids in the chain; it does not describe a shape.
Option (2) Secondary Structure — Incorrect. This is the local folding of the chain into an \( \alpha \)-helix or a \( \beta \)-pleated sheet, held by hydrogen bonds; the shape of the whole molecule comes from folding it further.
Option (4) Quaternary Structure — Incorrect. This is the arrangement of two or more polypeptide subunits with respect to each other, as in haemoglobin; many proteins have no quaternary structure at all.
NCERT (2026-27 edition):
Structure of Proteins – …
