Biology · Biomolecules · NEET
Four forces stabilize protein 3D folding: (1) hydrogen bonds, (2) ionic or electrostatic interactions (between +ve and -ve R-groups), (3) hydrophobic interactions (water-hating R-groups clump inside), and (4) disulphide (S-S) bridges between two cysteine amino acids. For NEET, remember disulphide is the only strong COVALENT one; the other three are weak interactions.
No. Ester bonds are NOT a force in protein structure. Ester bonds link fatty acids to glycerol in lipids (fats) and appear in the sugar-phosphate backbone of nucleic acids. So if NEET asks which is 'least likely' to stabilize protein 3D folding, the answer is ester bond. This exact trap came in NEET 2016.
A disulphide bridge is a strong COVALENT bond (S-S) between two cysteine R-groups, so it locks the fold firmly. A hydrogen bond is a WEAK interaction between H and O/N atoms. Both help folding, but disulphide is far stronger. In insulin, two chains are joined by disulphide bridges (NEET 2016), not by hydrogen bonds.
Some amino acid R-groups are non-polar (water-hating). In watery cell fluid they turn inward, away from water, and pack together in the protein core. This inward packing pulls the chain into a compact ball and stabilizes the 3D shape. It is a weak interaction but very important for keeping the fold together.
The disulphide bridge (S-S) is the strongest because it is a covalent bond. Hydrogen bonds, ionic interactions and hydrophobic interactions are all weak, non-covalent forces. This is why breaking disulphide bridges strongly unfolds (denatures) a protein.
The peptide bond builds the PRIMARY structure (it joins amino acids in a chain). It is not counted as a folding force for tertiary structure. Tertiary folding is stabilized by R-group interactions: hydrogen bonds, ionic, hydrophobic, and disulphide bridges.
Which of the following is the least likely to be involved in stabilizing the three-dimensional folding of most proteins?
The two polypeptides of human insulin are linked together by:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Hydrogen bonds, ionic (electrostatic) interactions, hydrophobic interactions, and disulphide (S-S) bridges. Only the disulphide bridge is a strong covalent bond; the other three are weak interactions.
No. Ester bonds occur in lipids (fatty acid + glycerol) and in the nucleic acid backbone, not in proteins. NEET has asked this as a trap.
A covalent S-S bond formed between the sulphur atoms of two cysteine amino acid R-groups. It strongly locks the protein's 3D shape and joins insulin's two chains.
The disulphide bridge is covalent (strong). Hydrogen bonds, ionic interactions and hydrophobic interactions are non-covalent (weak) but together they hold the fold.
The correct 3D fold decides the protein's biological activity (as an enzyme, hormone, etc.). NCERT states the right-handed helix and tertiary fold are necessary for many biological functions.
