GLOSSARY

A membrane hormone receptor is a transmembrane protein on the cell surface that recognises hydrophilic hormones (peptides, proteins, and catecholamines), which cannot cross the lipid membrane, and relays the signal into the cell via second messengers or kinase cascades.

Structure

• Extracellular domain: the hormone binding site.
• Transmembrane domain: 7 alpha-helices in GPCRs.
• Intracellular domain: couples to a G protein or has enzymatic activity (such as tyrosine kinase).

Signal Transduction Mechanisms