G Coupled Protein Receptors Flashcards
Why are G protein coupled coupled receptors also called 7TM receptors?
They have 7 transmembrane proteins
What is a ligand?
A molecule that interacts with a ligand
What is an agonist?
A molecule that binds to a receptor and activates it
What are antagonists?
Molecules which bind to the receptor but do not activate it
What abilities do agonists possess?
Efficacy and affinity
What do GPCRs respond to?
Sensory GPCRs sense light, odours and taste. They also respond to ions, neurotransmitters, peptide and non-peptide hormones and large glycoproteins.
What is the structure of a GPCR?
They are made up of a single polypeptide chain which creates 7-transmembrane spanning regions. Their is an extracellular N terminal and an intracellular C terminal
Where can a ligand bind in the receptor?
Either on the N terminal or they bind to amino acid side chains of the transmembrane domains
What change occurs after a ligand binds to the GPCR?
Conformation change (changes shape)
What can bind to activated GPCR receptors?
G proteins
What is the actual name of a G protein?
Guanine nucleotide binding protein
What are G proteins made up of?
Three subunits (alpha, beta and gamma) this makes them heterotrimeric
What happens to the G protein after it interacts with an activated GPCR?
The G protein itself is activated by causing GTP to exchange for GDP On the alpha subunit
What happens to the G protein immediately after the GDP is replaced with GTP?
The complex dissociates into an alpha GTP and beta gamma subunit which can then interact with effector proteins
Why do the G protein reactions occur on the plasma membrane?
All the substances are localised for a more efficient response
How is the G protein signal terminated?
The GTPase activity of the alpha subunit hydrolyses the GTP back to GDP. The GDP alpha subunit has a high affinity for the beta gamma subunit so the heterotrimeric complex reforms.
What are the 3 types of alpha subunits?
S (stimulates), I (inhibits) and q
What effector is stimulated when an s subunit is activated by Adrenaline or noradrenaline?
Adenylyl cyclase
What happened when adrenaline binds to a GPCR which activates an I G protein?
Adenylyl cyclase is inhibited
What happened when an adrenaline or noradrenaline molecule activates a q G protein?
Phospholipase C is activated.
Why can adrenaline and nor adrenaline have different affects when they bind to different GPCRs?
Different receptors recruit different versions of the alpha G protein subunit which causes different effects.
What effect does the toxin CTx have?
Stops the snag protein subunit hydrolysing GTP into GDP, therefore the 2 subunits de not reform and remain activated.
What does CTx stand for?
Cholera Toxin
What does PTx stand for?
Pertussis toxin
