Insulin: structure, production, secretion, and diabetes

Insulin as a peptide hormone

Insulin is a peptide hormone made by the beta cells of the pancreatic islets. In humans it is encoded by the INS gene and is a key anabolic hormone that regulates metabolism of carbohydrates, fats, and proteins. By promoting glucose uptake into liver, fat, and skeletal muscle cells, insulin helps convert absorbed glucose into glycogen (via glycogenesis) and fats/triglycerides (via lipogenesis), while also inhibiting liver glucose production when blood insulin is high. Structurally, human insulin is a heterodimer consisting of an A-chain and a B-chain linked by disulfide bonds, with a total length of 51 amino acids. It is synthesized as an inactive precursor (preproinsulin → proinsulin), then processed to remove the C-peptide and produce mature insulin. Functionally, insulin secretion is tightly coupled to blood glucose: high glucose stimulates release, while low glucose suppresses it. Loss of insulin activity leads to diabetes, including type 1 (autoimmune destruction of beta cells) and type 2 (impaired beta-cell function and insulin resistance).

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Insulin gene INS and human encoding

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