intracellular receptors - protein receptors within the cell
- signal molecules are usually lipid-soluble or very small in order to pass through the membrane
- gene regulating receptors - has binding site for DNA
- inhibitor protein may prevent DNA from binding
- either activates or suppresses certain genes after binding to DNA
- response varies depending on the cell
- lipid-soluble signal molecules tend to last longer than water-soluble signals
- regulators as enzymes - catalyzes reactions when activated
- nitric oxide binds to guanylyl cyclase, catalyzes synthesis of GMP (messenger molecule that relaxes smooth muscle cells)
cell surface receptors - accounts for the majority of a cell's receptors
- turns extracellular signals into intracellular ones
- water-soluble signals can't pass through the membrane, must bind w/ surface receptors
- chemically gated ion channels - allow ions through
- opens only when a neurotransmitter binds to it
- shape/charge of channel determines what type of ion goes through it
- enzymic receptors - activates an enzyme when binding to a signal molecule
- protein kinases - enzymes that add phosphate groups to proteins
- binds to signal molecule outside the school, enzyme activity occurs in the cytoplasm
G-protein linked receptors - uses GTP-binding protein to indirectly act on enzymes/ion channels
- starts a diffusible signal within the cell
- has short duration
- G-protein changes shape, leaves receptor once signal molecule arrives
- GTP can start few events, turns into GDP+phosphate very quickly
- pathway shuts down if signals stop coming in
- threads back and forth across the membrane 7 times (7-pass transmembrane protein)
- more of these surface receptors than any other kind
- may have evolved from sensory receptors of prokaryotes
- Rodbell/Gilman - received Noble prize for work w/ G-proteins
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