Physiology 7

Question 1

4 Superfamilies of receptor proteins and examples

Answer 1

• Ligand-gated ion channels (e.g nicotinic acetylcholine
  receptor)
• Receptors with intrinsic enzymic activity (e.g Insulin receptor)
• G protein-coupled receptors (7TM receptors) (e.g B-adrenoceptor)
• Nuclear receptors (e.g glucocorticoid receptor)

Question 2

Define Emax , EC50 , KD and Bmax

Answer 2

EC50 : effective concentration of ligand producing 50 of Emax (maximal response)
KD : (Dissociation constant, a measure of ligand affinity)
Bmax : maximum binding capacity – information about RECEPTOR NUMBER

Question 3

Common basic structure of a Gprotein receptor

Answer 3

Single polypeptide chain
(300-1200 amino acids)

7-transmembrane (7TM)-
spanning regions

Extracellular N-terminal

Intracellular C-terminal

Question 4

How do GPCRs alter cellular activity?

Answer 4

An activated GPCR must interact with another protein called a guanine-
nucleotide binding protein (G protein)
( they are ‘heterotrimeric’):
α (alpha), β (beta) and γ (gamma) subunits
The GPCR-G protein interaction activates the G protein by causing GTP to exchange for GDP on the G protein α subunit

Question 5

‘Off state’ and ‘On state’ structures of Gproteins?

Answer 5

Off state - GDP bound to a-subunit, a-subunit bound to Beta-gamma complex
On state - GDP exchanged for GTP, a-subunit and beta-gamma complex disassociate