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39 Cards in this Set
- Front
- Back
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gtp hydrolysis |
GTP + H2O <=> GDP + Pi |
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when is a GCPR turned on? |
when GTP is bound |
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G-protein coupled receptor signalling |
-when the signal molecule binds to the receptor there is a conformational shape change in the alpha subunit -this causes the release of a molecule of GDP -GTP molecule replaces the displaced GDP molecule -complex dissociates from the beta/lambda complex as well as from the receptor G-protein complex is described as 'active alpha-GTP subunit' |
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what happens to the active alpha-GTP subunit after it has been made |
-associate with specific target enzymes -target enzyme remains active whilst bound -propagates the signal - |
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signal transduction |
conversion of signals that carry information from one form into anther |
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what do target cells possess |
receptors recognise and respond specifically to the target molecule |
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what is paracrine signalling |
signal molecules do not enter the bloodstream signal molecules diffuse through the ECM signal molecules act as local mediators |
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autocrine signalling |
form of paracrine signalling where cells respond to the local mediators that they themselves produce cancer cells can sometimes promote their own growth in this way |
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neuronal signalling |
deliver messages over a long distance message delivered quickly to a specific destination |
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signal-mediated cell-to-cell communication |
most short range signalling method does not require the release of a secreted molecule cells make direct physical contact through signal molecules in the plasma membrane |
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two classes of ECM molecule |
-molecules too large/hydrophilic to cross the plasma membrane -molecules small and hydrophobic enough to cross the membrane |
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examples of steroid hormones |
cortisol estradiol testosterone |
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nuclear receptor |
when activated by a hormone binding they act as transcription regulators in the nucleus where hydrophobic molecules bind |
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describe the unstimulated state of the G protein |
alpha subunit has gdp bound to it the g protein is said to be idle |
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alpha subunit |
has intrinsic GTPase activity eventually, hydrolyses bound GTP to GDP returns whole G protein to its inactive state |
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activated G protein |
-alpha subunit loses affintiy for GDP GDP exchanged fo GTP activation breaks up a-b-y subunits activted a subunit, which is bound to GTP, detaches from by complex a & by now interact directly with target proteins |
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what does Gs do? |
stimulates the enzyme adenylyl cyclase |
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what does G1 do? |
inhibits adenyl cyclase |
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cyclic AMP pathway |
-activated a G protein (Gs) subunit switches on adenylyl cyclase -cAMP phophodiesterase terminates the signal |
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what does cAMP phosphodiesterase do? |
converts cAMP-> AMP |
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how does cAMP exert its effects |
-on PKA enzyme -binding of cAMP causes a conformational change - |
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what does PKA do? |
catalyses the phosphorylation of ser and thr on specific intracellular portiens |
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what does epinephrine do? |
binds to a class of GCPRs called 'adrengic' receptors prepares the body for action |
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inositol phospholipid pathway |
-triggers a rise in intracellular Ca2+ -affects G protein Gq -Gq activates membrane bound phospholipase C |
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what two messenger molecules does phosphholipase c produce? |
-inositol 1,4-5 triphosphate (IP3) -diacyglycerol (DAG) |
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what does inositol 1,4-5 triphosopahte do? |
-it is a water soluble molecule -binds to Ca2+ receptors on the ER causes an increase in cystolic Ca2+ |
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what does an activated phosphlipid do when active? |
cleaves a lipid molecule (inositol 1,4-5 triphospate |
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what dies duacylglycerol do? |
-remains in the plasma membrane -recruits and activate a protein kinase C (PKC) -PKC phosphorylates intracellular proteins |
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what happens when Ca2+ binds to calmdomium |
-protein undergoes a confromational change -can now interact with a range of proteins |
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CaM kinases |
ca2+/calmdomium dependent kinases -influence processes by phosphorylating other proteins |
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define a G protein |
a guanine nucleotide binding protein involved in signalling cascades |
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signalling cascades allow... |
allows amplification of the original signal take seconds to excute |
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what is rhodopsin |
a GCPR light receptor |
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enzyme coupled receptors (ECRs) |
-transmembrane proteins -display ligand binding domains on the outer surface of PM -no association of a G protein cytoplasmic domain acts as an enzyme |
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what processes are ECRs involved in? |
-growth -proliferation -differentiation -survival of cells in mammalian tissue |
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what do ECRs function as? |
local mediators |
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receptor tyrosine kinases |
-largest class of ECRs -phosphorylate tyrosines |
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describe ECR structure |
-have to switch on enzymatic activity there is only one transmembrane segment, which is an alpha helix the single alpha helix is poorly suited to transmit a conformational change |
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how do ECRs get round the poor suitablily of an alpha helix to transmit a confromational change? |
binding of a signal molecule causes the recpetor molecule to come together in the plasma membrane this forms a dimer brings the tails of two receptor molecules together the tails phosphorylate the tyrosines of each other |
