29 Questions
What is the main function of G protein coupled receptors (GPCRs)?
To bind to a wide array of molecules
How are G proteins activated by GPCRs?
Ligand binding changes the confirmation of the receptor, leading to activation of the GPCR
Which subunits are present in trimeric G proteins?
Alpha, beta, and gamma
What is the main function of adenylyl cyclase in the context of G protein activation?
To catalyze the formation of cyclic AMP from ATP
Where does the alpha and gamma subunits of trimeric G proteins anchor?
Into the leaflet of the lipid bilayer
What is the role of cAMP in G protein signaling?
To act as a secondary messenger
What causes activation of G proteins in the context of GPCR signaling?
GDP is removed from the alpha subunit and replaced by GTP
Which enzyme converts GTP to cGMP as a secondary messenger?
Phosphodiesterase
What molecule is formed when cAMP is further hydrolysed by cyclic AMP phosphodiesterase?
Monomeric AMP
Which G protein family stimulates adenylate cyclase?
Gs
What activates the Gq/11 family of G proteins?
Phospholipase C beta (PLCb)
What is the function of calmodulin when activated by Ca2+?
Modulates activity of different proteins
What is the role of phosphodiesterase when activated by light in the vision process?
Converts cGMP to GMP
In the vision process, what happens when cGMP levels decrease?
Sodium channels close
How does an influx of ions across the membrane affect the membrane potential?
Increases the membrane potential
What is the function of G protein coupled receptors (GPCRs)?
Activation of downstream signaling pathways
How are G proteins activated by GPCR's?
Binding of GTP to the alpha subunit
What is the role of adenylyl cyclase in G protein activation?
Formation of cyclic AMP from GTP
How does an active GPCR affect G proteins?
Induces dissociation of beta subunit from the alpha subunit
What is the main function of trimeric G proteins?
Anchoring of alpha and beta subunits in the lipid bilayer
Where are the alpha and gamma subunits of trimeric G proteins anchored?
Into the leaflet of the lipid bilayer by lipid modifications
What is the role of Guanine nucleotide exchange factor (GEF) in G protein signaling?
Replaces GDP with GTP for G protein activation
How does cAMP influence gene expression?
By phosphorylating their targets
What is the function of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3) as second messengers?
Both activate protein kinase C
How do G proteins control channel opening?
By directly binding to the channel and modulating activity
What happens when cGMP levels decrease in the vision process?
PDE counter reacts and converts cGMP to GMP
What is the main function of Gq/11 family of G proteins?
Stimulates phospholipase C beta (PLCb)
How does an influx of ions across the membrane affect the membrane potential?
Depolarizes the membrane
What is the function of cyclic AMP phosphodiesterase in the context of cAMP signaling?
Hydrolyses cAMP into monomeric AMP
Study Notes
G Protein Coupled Receptors (GPCRs)
- GPCRs are a large family of transmembrane receptors that sense molecules outside the cell and activate intracellular signaling pathways
- The main function of GPCRs is to transmit signals from outside the cell to the inside, leading to various cellular responses
G Protein Activation
- G proteins are activated by GPCRs through a conformational change in the receptor, allowing the G protein to bind to the receptor
- Activation of G proteins by GPCRs leads to the exchange of GDP for GTP, causing the G protein to dissociate from the receptor
Trimeric G Proteins
- Trimeric G proteins consist of three subunits: alpha, beta, and gamma
- The alpha subunit binds to GTP, while the beta and gamma subunits are involved in anchoring the G protein to the plasma membrane
- The alpha and gamma subunits of trimeric G proteins anchor to the plasma membrane through lipid modifications
Adenylyl Cyclase and cAMP Signaling
- Adenylyl cyclase is an enzyme that converts ATP to cAMP, a secondary messenger, in response to G protein activation
- cAMP plays a key role in G protein signaling, influencing gene expression, ion channel opening, and other cellular responses
- cAMP is further hydrolyzed by cyclic AMP phosphodiesterase to form 5'-AMP
G Protein Families and Signaling
- The Gs family of G proteins stimulates adenylate cyclase, leading to an increase in cAMP levels
- The Gq/11 family of G proteins activates phospholipase C, leading to the formation of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3) as second messengers
- The Gi family of G proteins inhibits adenylate cyclase, leading to a decrease in cAMP levels
- Guanine nucleotide exchange factor (GEF) facilitates the exchange of GDP for GTP, activating the G protein
G Protein Signaling and Channels
- G proteins control channel opening by interacting with and modifying the channel proteins
- An influx of ions across the membrane affects the membrane potential, leading to changes in cellular responses
Vision Process
- In the vision process, cGMP is converted from GTP by the enzyme guanylyl cyclase
- cGMP levels decrease in response to light, leading to the closure of ion channels and hyperpolarization of the membrane
- Phosphodiesterase, activated by light, breaks down cGMP, leading to a decrease in cGMP levels
Calmodulin and Phosphodiesterase
- Calmodulin, when activated by Ca2+, activates enzymes involved in the signaling cascade
- Phosphodiesterase, activated by light, breaks down cGMP, leading to a decrease in cGMP levels
Test your knowledge about G Protein Coupled Receptors (GPCRs), the largest class of human cell surface receptors, which are involved in various physiological processes and are targeted by many drugs. Learn about the structure, function, and signaling mechanisms of these important receptors.
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