Answer: Hydrogen bonds between NH and C=O groups.
- A Hydrogen bonds between NH and C=O groups
- B Covalent disulfide bonds between cysteine side chains
- C Ionic bonds between charged side chain residues
- D Weak van der Waals forces between nonpolar side chains
Correct answer: A. Hydrogen bonds between NH and C=O groups
Explanation: The alpha-helix is stabilised by intramolecular hydrogen bonds between the backbone NH and C=O.
Two amino acids join via a condensation reaction: the carboxyl -OH of one and an amine -H of the other are eliminated as water, leaving a peptide bond (-CO-NH-) linking them into a dipeptide; repeating this builds a full protein chain.
Concept context
The chemistry of life: carbohydrates, proteins, lipids, nucleic acids, enzymes, and vitamins. Understand their structures, classification, and biological functions. Highly relevant for NEET and Class 12 board exams.