GLOSSARY

Peptide and Protein Hormones
Peptide and protein hormones are chains of amino acids synthesized through gene expression and translation. Their lengths and modifications vary, with insulin, glucagon, growth hormone and several pituitary hormones providing familiar examples.

Production and release

Many begin as larger precursor molecules. Processing in the endoplasmic reticulum, Golgi apparatus and secretory granules produces the releasable product. A suitable stimulus can trigger calcium-dependent exocytosis, although the exact coupling mechanism differs among cell types.

How targets respond

Most act through cell-surface receptors because they do not freely cross the lipid bilayer. Receptor families differ. Insulin uses a receptor tyrosine kinase, while growth hormone acts through a cytokine receptor associated with JAK2.

Functional importance

Some peptide signals act rapidly on existing proteins and also generate longer-term transcriptional changes. Thus, classifying a hormone as a peptide does not mean that every effect is immediate or that no gene regulation is involved.