The hormone insulin is a:

Insulin is a peptide hormone composed of 51 amino acids arranged in two polypeptide chains (A and B) linked by disulfide bonds; it is synthesized in pancreatic beta cells as preproinsulin that is processed to proinsulin and then mature insulin [1]. Biochemical and clinical sources explicitly identify insulin as a peptide/protein hormone secreted by β‑cells of the pancreas and widely used therapeutically in diabetes management [3]. Chemically it is nonglycosylated and proteinaceous, so it is not a glycolipid, fatty acid, or steroid. Insulin acts via specific cell‑surface receptors to promote glucose uptake and glycogen synthesis, consistent with peptide hormones’ mechanisms. Therefore the correct classification is “Peptide.”

Sources

1. [1] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/human-insulin
2. [2] https://pubchem.ncbi.nlm.nih.gov/compound/Insulin
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > Do You Know? > p. 110