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Flashcards in Intracellular Signalling- G Proteins Deck (9)
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Describe how G-Proteins in general produce a cellular response and how the response stops

1. GPCR activated by ligand
2. GDP is exchanged for GTP, activating G-protein
3. Alpha-GTP subunit and Beta-Gamma subunit formed
4. Send signals to effectors
5. GTPase removes Pi from Alpha-GTP—> Alpha-GDP
6. Alpha-GDP and Beta-Gamma recombine to form inactive G-protein


Explain how Cholera Toxin and Pertussis Toxin affect G-Protein function

CTx: Stops GTPase function, so constant signals to effectors from Alpha s-GTP subunits

PTx: Stops GDP exchange for GTP, on Alpha-i subunits, so no Gi-protein activation


Describe the function of Gs-Protein coupled receptors

1. GPCR activated
2. GDP exchanged for GTP-> GTP-Alpha s subunit produced
3. GTP-Alpha s activates Adenylyl Cyclase to make cAMP from ATP
4. cAMP stimulates PKA (Binds to R region, C subunits dissociate to phosphorylate target proteins)


Describe the function of Gi-Protein coupled receptors

1. GPCR activated
2. GDP-Alpha i ————> GTP-Alpha i - subunit
3. GTP-Alpha i subunit inhibits Adenylyl Cyclase, so no cAMP


Describe the function of Gq -Protein coupled receptors

1. GPCR activated
2. GDP-Alpha q———> GTP-Alpha q subunit
3. This subunit stimulates PLC, which hydrolyses PIP2->DAG + IP3
4. IP3 diffuses to + opens IP3 Receptors on ER, increasing Cytoplasm Ca
5. DAG moves along membrane, and with Ca, activates PKC
6. PKC phosphorylates its substrates


Explain how Inotropy, Chronotropy and Vasodilation are affected by Adrenaline/ Noradrenaline?

1. Interact with Beta-1 receptors, activating Gs Proteins
2. Adenylyl Cyclase stimulated, more cAMP, PKA activated
3. PKA causes Vasodilation AND phosphorylates VOCC
4. VOCC activated, Ca enters cell-> (+)ve Inotropy, Chronotropy


Outline the effects Noradrenaline and Acetylcholine on smooth muscle contraction

Noradrenaline interacts with Vascular Alpha-1 Adrenoceptors to cause Vasoconstriction

Acetylcholine interacts with Smooth muscle M3-Muscarinic receptors to cause Bronchoconstriction


Describe the structure of a G-Protein?

Heterotrimer: 3 Subunits; Alpha, Beta, Gamma

Alpha-GTP bonded to Beta-Gamma, which function as a singular subunit


Explain how Morphine affects Neurotransmitter release

Morphine activates GPCR
GTP-Alpha i subunit produced + Beta-Gamma subunit
Beta-Gamma inhibits VOCC—>Reduced Ca influx-> Reduced Neurotransmitter exocytosis