G-Protein Linked Receptors Flashcards
G-protein linked receptors have how many transmembrane proteins?
seven-pass
What do g-protein-linked receptors contain?
extracellular domain w/ ligand binding site and an intracellular domain w/binding site for a heterotrimeric G-protein.
What do heterotrimeric G-proteins do?
Couple the receptor to their cytosolic targets, which are commonly ion channels or enzymes
What do heterotrimeric G-proteins consist of and what do they do?
alpha-subunit - mediate signaling in most signaling pathways.
Beta gamma subunits - mediate signaling in some signaling pathways.
What initiates g-protein subunit dissociation?
GTP/GDP exchange
When is the G-protein switched off?
When the GDP is bound to the alpha subunit
Activation of the G-protein causes what?
exchange of GTP for GDP
What happens when GTP is bound?
the G-protein is switched on, alpha and beta-gamma subunits dissociate
How does the G-protein switch off?
What happens when GDP is bound to alpha subunit?
What happens when it is switched off?
By hydrolyzing GTP to GDP. GDP remains bound to alpha subunit. Alpha subunit possesses GTPase activity, which does the hydrolyzing of GTP to GDP.
Re-associates with the beta-gamma subunit
What does If do?
funny current or pacemaker current drives the potential toward threshold
Ica,L, what does it do?
L-type Ca2+ current activates at threshold and generates action potential
What increases cardiac beat frequency?
Norepinephrine released from sympathetic fibers .
Stimulation of If and Ica,L does what?
increases rate of pacemaker cell depolarization
What does norepinephrine do?
activates the B1-adrenergic receptor
What does the activated receptor do?
interacts with and activates Gs, a stimulatory G-protein.
What is GDP replaced by?
GTP
What does Gs dissociate into?
alpha and beta/gamma subunit.
GTP-bound alpha subunit stimulates what?
stimulates adenylyl cyclase to catalyze the generation of the second messenger cAMP from ATP
What does cAMP bind and enhance?
To account for what?
camp binds to and enhances the rate of HCN channel activation to account for the change in kinetics of the funny current and increase the rate of depolarization.
What does camp bind to that activates the catalytic subunit?
cAMP binds to the regulatory subunit of protein kinase A and the catalytic subunit becomes active.
What does PKA phosphorylate and what happens after this?
PKA phosphorylates Cav1 channels, which changes their activity and accounts for change in Ica, L which contributes ot the rate of depolarization.
How is greater activity involved in increasing heart rate?
Greater activity enhances the rate of the membrane depolarization to increase the heart rate.
Gs/cAMP Pathway- what dissociate from the receptor?
the ligand and norepinephrine.
Gs/cAMP Pathway- What part of the g-protein inactivates itself and how?
the alpha-subunit of the g-protein inactivates itself by hydrolyzing GTP to GDP
