Cell signalling 2(?) Flashcards
LOs:
- A basic understanding of how monomeric G-proteins are activated & inactivated using GEFs & GAPs
- Structure of trimeric G proteins and of G-protein coupled receptors
- Activation of a GPCR & how this activates a trimeric G protein
- Examples of 2nd messengers & how cAMP is produced
- The effect of cAMP of PKA
- Basic structures of RTKs
- How RTKs are activated & are able to activate signal transduction pathways
What binds to G-protein coupled receptors initially?
Ligand (first messenger)
What happens to G-protein coupled receptors when ligand binds to it?
Activates an intracellular G-protein which in turn activates an enzyme which changes the conc of an intracellular second messenger (small molecule e.g. cAMP)
What is the structure of a G-protein coupled receptor?
- 7 transmembrane alpha helical regions
- 4 extracellular regions (on the outside of the cell between alpha regions)
- 4 cytosolic regions (loop into cell, same as above)
What are 4 examples of stimuli (ligands) in GPCR systems?
- Adrenaline
- Light
- fMet peptide
- ACh
For adrenaline (as a GPCR stimulus) name the:
Receptor, effector, 2nd messenger & response in the system:
Stimulus = adrenaline
Receptor = beta-adrenergic
Effector = adenylate cyclase
2nd messenger = cAMP
Response = glycogen breakdown
For light (as a GPCR stimulus) name the:
Receptor, effector, 2nd messenger & response in the system:
Stimulus = light
Receptor = rhodopsin
Effector = cGMP phosphodiesterase
2nd messenger = cGMP
Response = photo-reception
For fMet peptide (as a GPCR stimulus) name the:
Receptor, effector, 2nd messenger & response in the system:
Stimulus = fMet peptide
Receptor = chemotactic receptor
Effector = phospholipase C
2nd messenger =IP3 (Ca2+) & DAG
Response = chemotaxis
For ACh (as a GPCR stimulus) name the:
Receptor, effector, 2nd messenger & response in the system:
Stimulus = ACh
Receptor = muscarinic ACH receptor
Effector = K+ channel
2nd messenger = K+
Response = slowing pacemaker activity
What state are G-protein receptors in when GDP is bound?
“Inactive” - the system is considered off
What state are G-protein receptors in when GTP is bound?
“Active” - the system has been switched on
The active G-protein has intrinsic GTPase activity
What are the 2 types of GTP-binding proteins?
- Monometric
- Trimetric
How G-proteins regulate how fast they act?
By how quickly they switch out GDP for GTP
GTP activates the receptor - therefore the faster it is switched in the more the receptor will react
What are GAPs and what do they do?
GTPase activating proteins
Inactivate the G protein by stimulating hydrolysis of GTP to GDP
What are GEFs and what do they do?
Guanine nucleotide exchange factors (GEFs)
Activate the G protein by stimulating it to release GDP
What is the trimeric structure of G proteins?
3 subunits:
Alpha, beta & gamma
How are the beta & gamma subunits in a G-protein arranged?
Beta & gamma are very tightly bound
What is the role of the beta and gamma unit?
To encourage the breakdown of GTP to GDP
Where are G-proteins attached to?
The cytoplasmic face of the plasma membrane
Describe the process of G protein relay signals:
- G protein attached to cytoplasmic face of the plasma membrane
- Alpha & beta subunits have covalently attached lipid molecules that aid binding to the plasma membrane
- Activation of G protein, via receptor activation
- Inactivation of G protein by GTP hydrolysis by alpha-subunit
(beta-gamma complex may dissociate)
What is the process of G protein receptors creating a second messenger system?
- Binding of ligand to GPCR changes the conformation of the receptor
- Allows GDP to be exhanged for GTP (acts as a GEF)
- alpha & beta-gamma subunits may dissociate (but not always)
- Activated G protein elicits a second messenger system
What are DAG and IP3 derived from?
A lipid
What does DAG generally do?
Floats around & stimulates protein kinase C
What does IP3 generally do?
Diffuse thru cytosol & reach endoplasmic reticulum, will allow calcium to diffuse into the cell
What is cAMP produced from?
Produced from ATP by adenylyl (adenylate) cyclase, releaseing pyrophosphotase
cAMP conc is kept low
What do phosphodiesterases do?
Cleave cAMP to 5’ AMP
Breaks down cAMP
Look at the diagram for activation of adenylyl cyclase by trimeric G protein :)
COol
What is the effect of cAMP?
- Activate cAMP-dependent protein kinases (PKA)
- PKA exists in inactive form but binding of cAMP causes dissociation of regulatory subunits
How is protein kinase A broken down?
PKA has 4 subunits - 2 are regulatory cAMP removes these 2 & allows active areas to go off
Protein kinase 2, the A kinase acts w A kinase anchoring proteins, gets locked onto these so it will do the jobs it’s required to do
What is the effect of activated PKA?
Ligand arrives, leads to adenylyl cyclase activated - using ATP cAMP is activated & stimulates various other molecules
Some genes known to respond when cAMP is present, these ones have CREb transcription factors
What are the actions of activated PKA?
- PKA can phosphorylate target proteins e.g. metabolic enzymes in glycogen metabolism
- Alter gene transcription cia cAMP response element binding protein (CREB)
What does RTKs stand for?
Receptor Tyrosine Kinases
Go from RTKs
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