G Proteins Flashcards
How many polypeptide chains do most tyrosine kinase receptors have?
1
Which subunit does insulin bind to?
Alpha
Describe agonists
Bind and activate receptors
Have affinity and efficacy
Name a beta 2 adrenoceptor agonist
Salbutamol
Name a m-opioid receptor agonist
Morphine
Describe antagonists
Bind but do not activate
Have affinity but no efficacy
Block the action of agonists
Name a beta adrenoceptor antagonist
Propranolol
Describe the common topology of GPCPs
N terminal is outside cell
7 TMDs
Single polypeptide chain
C terminal is intracellular
What are the 2 regions where ligands can bind?
Between TMDs
N terminal region
How is G protein signalling terminated?
Alpha subunit has an intrinsic GTPase
Hydrolyses the GTP after about 3-4 secs
Has a higher affinity for the beta-gamma subunit when bound to GDP therefore they bind and that prevents further signalling
What type of G protein does rhodopsin accompany?
G alpha t
How does pertussis toxin (whooping cough) interfere with G protein function?
Bind to G alpha i proteins
Prevents GTP binding therefore they cannot be activated
How does cholera toxin interfere with G protein function?
Interferes with GTPase of G alpha s proteins
GTP cannot be hydrolysed therefore the proteins remain activated
What are the 3 superfamilies of cell-surface receptors?
LG ion channels
Receptors with intrinsic enzyme activity
GPCRs (7TMDs)
Give 3 examples of Gs coupled receptors?
Beta adrenoceptors
D1 dopamine receptors
H2 histamine receptors
