Insulin (human)

In plain language

Insulin is a hormone made by the pancreas that moves sugar from the blood into cells for energy. People with type 1 diabetes cannot make it, and some with type 2 do not respond well to it, so insulin was turned into a medicine.

Insulin is a small protein, a chain of 51 amino acids in two pieces. It was discovered in 1921 and first given to a patient in 1922, saving the life of a 14-year-old boy. Today it is made in factories using engineered bacteria and it is on the WHO's list of essential medicines.

For students

Human insulin is a 51-residue, two-chain peptide hormone (about 5,808 Da for the native hormone; 5,794 Da is commonly cited for the 51-residue peptide), secreted by pancreatic beta cells in response to rising blood glucose. The A chain (21 residues) and B chain (30 residues) are held together by two disulfide bonds, with a third inside the A chain.

It signals through the insulin receptor, a tyrosine kinase that triggers PI3K-Akt and MAPK pathways, driving glucose uptake in muscle and fat, glycogen storage, and protein synthesis while suppressing liver glucose output. Synthetic insulin analogues (lispro, aspart, glulisine for meals; glargine, detemir, degludec for background coverage) modify self-association and absorption rather than receptor activity. Recombinant human insulin entered care in 1982, and modern biosimilar competition has made it the template for peptide drug development, pricing policy and biosimilar regulation.

For researchers and instructors

Biochemistry. The A and B chains are produced as a single proinsulin precursor, folded, then cleaved at two sites to release the connecting C-peptide; the mature hormone's activity depends on the correct disulfide pairing (A6-A11, A7-B7, A20-B19).

Pharmacology. Regular insulin's pharmacodynamic delay comes from hexamer self-association at the injection site; prandial analogues destabilize hexamers for faster absorption, while basal analogues shift solubility or add albumin-binding side chains for prolonged, flat profiles.

Human evidence. Over a century of randomized trials across type 1 and type 2 diabetes, plus the DCCT/EDIC and UKPDS programs, establish its efficacy and the relationship between glycemic control and complications.

Teaching point. Insulin is the canonical example used to teach structure-activity relationships, recombinant protein production, biosimilarity and drug pricing policy.