Answer: The amino group accepts a proton from the carboxyl group intramolecularly.
- A The amino group accepts a proton from the carboxyl group intramolecularly
- B An external acid molecule donates a proton to the amino group in standard practice
- C The hydrophobic R group ionises under physiological pH under most conditions encountered
- D Surrounding water molecules donate protons to both ends as frequently observed in practice
Correct answer: A. The amino group accepts a proton from the carboxyl group intramolecularly
Explanation: In a zwitterion, the -COOH donates a proton to the -NH<sub>2</sub> group, giving -COO- and -NH<sub>3</sub><sup>+</sup>.
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.