Summarizing How Hormones Work

Summary

Hormones cause cellular changes by binding to receptors on target cells. The number of receptors on a target cell can increase or decrease in response to hormone activity. Hormones can affect cells directly through intracellular hormone receptors or indirectly through plasma membrane hormone receptors.

Lipid-derived (soluble) hormones can enter the cell by diffusing across the plasma membrane and binding to DNA to regulate gene transcription and to change the cell’s activities by inducing production of proteins that affect, in general, the long-term structure and function of the cell. Lipid insoluble hormones bind to receptors on the plasma membrane surface and trigger a signaling pathway to change the cell’s activities by inducing production of various cell products that affect the cell in the short-term. The hormone is called a first messenger and the cellular component is called a second messenger. G-proteins activate the second messenger (cyclic AMP), triggering the cellular response. Response to hormone binding is amplified as the signaling pathway progresses. Cellular responses to hormones include the production of proteins and enzymes and altered membrane permeability.

Glossary

adenylate cyclase

an enzyme that catalyzes the conversion of ATP to cyclic AMP

down-regulation

a decrease in the number of hormone receptors in response to increased hormone levels

first messenger

the hormone that binds to a plasma membrane hormone receptor to trigger a signal transduction pathway

G-protein

a membrane protein activated by the hormone first messenger to activate formation of cyclic AMP

hormone receptor

the cellular protein that binds to a hormone

intracellular hormone receptor

a hormone receptor in the cytoplasm or nucleus of a cell

phosphodiesterase (PDE)

enzyme that deactivates cAMP, stopping hormone activity

plasma membrane hormone receptor

a hormone receptor on the surface of the plasma membrane of a cell

up-regulation

an increase in the number of hormone receptors in response to increased hormone levels