Q.42 Which of the following is/are peptide hormone(s)?
(A) Calcitonin
(B) Glucagon
(C) Serotonin
(D) Thyroxine

Calcitonin and glucagon qualify as peptide hormones, making options (A) and (B) correct in this CSIR NET Life Sciences question. Peptide hormones consist of amino acid chains synthesized as polypeptides, acting via cell surface receptors unlike lipid-soluble hormones. This MCQ tests hormone classification basics essential for biochemistry sections.

Option Analysis

Calcitonin (A): Correct. Calcitonin is a 32-amino acid peptide hormone produced by thyroid C cells, lowering blood calcium by inhibiting osteoclasts. Its structure features an alpha helix and disulfide bond, confirmed by sequencing.

Glucagon (B): Correct. Glucagon, a 29-amino acid peptide from pancreatic alpha cells, raises blood glucose via glycogenolysis. Derived from proglucagon, it binds G-protein-coupled receptors.

Serotonin (C): Incorrect. Serotonin (5-HT) is a monoamine neurotransmitter derived from tryptophan, not a peptide chain. Synthesized by tryptophan hydroxylase, it functions as an indoleamine.

Thyroxine (D): Incorrect. Thyroxine (T4) is an iodinated tyrosine derivative, classified as an amino acid-derived hormone with lipid-like solubility. It diffuses into cells to bind nuclear receptors, unlike water-soluble peptides.

Correct Answer

Options (A) and (B) identify peptide hormones. Standard CSIR NET format expects multiple correct selections where “is/are” indicates both apply. Single peptides like insulin exemplify this class; chains over 100 residues become protein hormones, but both activate second messengers.

Hormone Classification Table

Exam Relevance

Peptide hormones dominate water-soluble categories in CSIR NET, contrasting steroid/thyroid hormones. Recall: peptides/proteins bind membrane receptors; distinguish via structure (chains vs. rings/modified singles). Practice similar MCQs on insulin, oxytocin for mastery.