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The addition of the nonhydrolyzable GTP-analog, GTPγS (shown below), is a common cell culture technique. If only affecting the inhibitory pathway, what effect would GTPγS have on cellular cAMP levels?
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12. Biosignaling
Inhibitory Adenylate Cyclase GPCR Signaling
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How does GPCR termination differ from GPCR desensitization?
A
GPCR termination promotes GPCR signaling while GPCR desensitization overexpresses the GPCR.
B
GPCR desensitization involves degradation of the GPCR while GPCR termination promotes GTPase activity of Gα.
C
GPCR termination blocks the GTPase activity of Gα while GPCR desensitization promotes ligand binding.
D
GPCR termination resets the signaling pathway in the absence of ligand, whereas GPCR desensitization dampens the cell response even in the presence of ligand.
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Understand the role of GPCRs (G-protein coupled receptors) in cell signaling. They are activated by ligands and initiate a cascade of intracellular events.
GPCR termination refers to the process that resets the signaling pathway. This occurs when the ligand is no longer present, and involves the promotion of GTPase activity of the Gα subunit, converting GTP to GDP, thus inactivating the G-protein.
GPCR desensitization is a mechanism that reduces the receptor's responsiveness to continuous or repeated stimulation by a ligand. This can occur even when the ligand is still present, often through receptor phosphorylation and binding of arrestin proteins.
Compare the two processes: Termination is about stopping the signal when the ligand is absent, while desensitization is about reducing the signal even when the ligand is present.
Consider the physiological implications: Termination ensures that signaling pathways are reset for future activation, while desensitization prevents overstimulation and potential cellular damage from continuous signaling.
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