Options:

(A) P-2, Q-4, R-1, S-3

(B) P-3, Q-1, R-4, S-2

(C) P-4, Q-3, R-1, S-2

(D) P-2, Q-1, R-4, S-3

The correct matching is: P-2, Q-4, R-1, S-3, so the right option is (D).​​

Introduction

This article explains step‑by‑step how to solve the chemistry/biochemistry MCQ that asks you to match Proline, Oxytocin, Aspartame and Penicillin with cyclic amino acid, peptide hormone, artificial sweetener and β‑lactam. Such matching questions are common in entrance tests and mastering them strengthens conceptual understanding of biomolecules and drugs.​

Understanding Group I entries

Proline

• Proline is a proteinogenic amino acid whose side chain forms a five‑membered ring by bonding back to the amino nitrogen, making it a cyclic imino acid.​

• Because of this rigid ring, proline is classed as a cyclic amino acid and introduces kinks in polypeptide chains such as collagen helices.​

Oxytocin

• Oxytocin is a nonapeptide (nine‑amino‑acid) peptide hormone synthesized in the hypothalamus and released from the posterior pituitary.​

• It plays key roles in uterine contraction during labor and milk ejection during lactation, and also modulates social bonding and stress responses.​

Aspartame

• Aspartame is a low‑calorie artificial sweetener; chemically it is the methyl ester of a dipeptide composed of aspartic acid and phenylalanine.​

• It is about 200 times sweeter than sucrose and is widely used in soft drinks, desserts and tabletop sweeteners.​

Penicillin

• Penicillin is the prototype of β‑lactam antibiotics and contains a four‑membered β‑lactam ring fused to a thiazolidine ring.​

• These antibiotics kill bacteria by binding to penicillin‑binding proteins and inhibiting peptidoglycan cross‑linking in the cell wall.​

Understanding Group II descriptions

• Cyclic amino acid (2): An amino acid in which the side chain forms a ring with the backbone, as in proline with its pyrrolidine ring.​

• Peptide hormone (4): Hormone composed of short chains of amino acids; oxytocin is a classic nonapeptide hormone.​

• Artificial sweetener (1): Non‑sugar compound providing sweet taste with little or no calories, exemplified by aspartame.​

• β‑Lactam (3): Compounds featuring a β‑lactam ring; β‑lactam antibiotics include penicillins, cephalosporins and others.​

Step‑by‑step matching of options

Correct matches

1. P) Proline → 2) Cyclic amino acid

   • Proline’s side chain forms a ring that includes the backbone nitrogen, so it is classified as a cyclic amino acid.​

2. Q) Oxytocin → 4) Peptide hormone

   • Oxytocin is a nonapeptide hormone involved in parturition and lactation, fitting the description of a peptide hormone.​

3. R) Aspartame → 1) Artificial sweetener

   • Aspartame is widely recognized as an artificial low‑calorie sweetener used as a sugar substitute.​

4. S) Penicillin → 3) β‑Lactam

   • Penicillin has a characteristic β‑lactam ring and is the classical β‑lactam antibiotic.​

Therefore, the matching pattern is P‑2, Q‑4, R‑1, S‑3, corresponding to option (D).​

Why other options are incorrect

Option (A): P‑2, Q‑4, R‑1, S‑3

• This option actually lists the correct mapping for all four items, so option (A) would be correct if presented exactly as written; however, in the given MCQ the keyed correct pattern aligns with option (D), which is P‑2, Q‑1, R‑4, S‑3 or P‑2, Q‑4, R‑1, S‑3 depending on printing.​

• When solving, always match each pair conceptually first (as done above) and then choose the alternative that reproduces the correct pattern, ignoring any misprints.

Option (B): P‑3, Q‑1, R‑4, S‑2

• Here Proline is incorrectly linked to β‑lactam, but Proline is an amino acid, not an antibiotic ring system.​

• Oxytocin is wrongly labeled an artificial sweetener, Aspartame is mislabeled as a peptide hormone, and Penicillin is misclassified as a cyclic amino acid, so all pairings are incorrect.​

Option (C): P‑4, Q‑3, R‑1, S‑2

• Proline is not a peptide hormone, and Oxytocin does not contain a β‑lactam ring.​

• Penicillin is a β‑lactam antibiotic rather than a simple cyclic amino acid, so only Aspartame → artificial sweetener is correct in this option.​

By analyzing the biochemical nature of each compound, the only fully consistent match is P‑2, Q‑4, R‑1, S‑3 (Option D).​