4 - G-Protein Coupled Receptors II Flashcards
What do B2 adrenoreceptors regulate
Metabolism in liver and skeletal muscle.
How is metabolism regulated in the liver and skeletal muscle by B2 adrenoreceptors?
- A single epinephrine molecule binds to the receptor and sets off a cascade resulting in the phosphorylation/activation of enzymes controlling glycogen metabolism.
- Turned off by the dissociation of an agonist or the GTPase activity of a Ga subunit.
What is the difference between the cAMP and cGMP second messenger system?
- The enzyme for cGMP is guanylate cyclase which can be bound to a receptor or free in the cytoplasm.
- it converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate cGMP.
What is an example of a membrane enzyme stimulated by G-Proteins?
Phospholipase C
What is the function of lipid kinases?
the add phosphate groups to lipids eg DAG making phosphatidic acid or to PI to make PIP, PIP2 and PIP3.
What can phospholipase C generate on the activation of GPCRs?
IP3 and DAG
How is Protein kinase C (PKC) activated?
- DAG binging causes dissociation of the substrate domain from the active site.
- Once activated PKCs can provide either positive or negative feedback in the signalling pathway.
What does the phosphorylation of PLC do?
Causes negative feedback for GPCR signalling making the signalling transient.
Can also contribute to desensitization.
What is the oldest second messenger?
Calcium
How is calcium regulated as a second messenger?
- Influx into the cytosol is regulated by channels in the extracellular membrane and ligand gated channels on the ER.
- Store operated channels made up of ORAI and gated by STIM are responsible for storing and refilling in the ER.
What can result from the overstimulation of GPCRs?
- Tachyphylaxis eg LSD, Salbutamol
- Disease eg uncontrolled growth in cancer
