06: cell signalling

glycoprotein

protein with carbohydrate attached

glycolipid

lipid with carbohydrate attached

endocrine

cell targets a distant cell through the bloodstream

paracrine

cell targets a nearby cell

autocrine

cell targets itself

juxtacrine

cells must physically interact to initiate signalling

ion channels

• allow ions to cross the lipid bilayer

• found in excitable cells

• chemical mechanical stimulus = electrical signals

leakage channel

always open

voltage-gated channel

opens (transiently) in response to change in the membrane voltage (membrane potential)

ligand-gated channel

opens (closes) in response to a specific extracellular neurotransmitter

signal-gated channel

opens (closes) in response to a specific intracellular molecule

G-protein coupled receptors

• transmembrane proteins with seven transmembrane domains

• fourth largest superfamily of proteins

• associate with heterotrimeric G proteins (alpha, beta, gamma subunits)

norepinephrine beta-adrenergic receptor

couples to the G_s subunit and activates adenylyl cyclase, which initiates downstream cellular effects

norepinephrine alpha 2-adrenergic receptor

couples to the G_i subunit and inhibits adenylyl cyclase, which prevents downstream cellular effects

norepinephrine alpha 1-adrenergic receptor

couples to the G_q subunit and activates phospholipase C, which initiates downstream cellular effects

receptor tyrosine kinases

enzyme-linked receptors

cross-phosphorylation

RTK in dimer phosphorylates tyrosines on other RTK

SH2 domain

• phosphotyrosine recognition domain

• located in some intracellular signal transducing proteins

• allows proteins to bind to phosphorylated tyrosines

nuclear receptors

• ligand-regulated transcription factors

• ligands can cross the plasma membrane

• ligands directly interact with nuclear receptors in the cell

orphan receptors

nuclear receptors with no known ligand

intracellular signal transduction

• propagate and amplify signal initiated by ligand binding receptor

• connects the cell surface to nucleus = changes in gene expression in response to extracellular stimuli