G Coupled Protein Receptors

Question 1

Why are G protein coupled coupled receptors also called 7TM receptors?

Answer 1

They have 7 transmembrane proteins

Question 2

What is a ligand?

Answer 2

A molecule that interacts with a ligand

Question 3

What is an agonist?

Answer 3

A molecule that binds to a receptor and activates it

Question 4

What are antagonists?

Answer 4

Molecules which bind to the receptor but do not activate it

Question 5

What abilities do agonists possess?

Answer 5

Efficacy and affinity

Question 6

What do GPCRs respond to?

Answer 6

Sensory GPCRs sense light, odours and taste. They also respond to ions, neurotransmitters, peptide and non-peptide hormones and large glycoproteins.

Question 7

What is the structure of a GPCR?

Answer 7

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

Question 8

Where can a ligand bind in the receptor?

Answer 8

Either on the N terminal or they bind to amino acid side chains of the transmembrane domains

Question 9

What change occurs after a ligand binds to the GPCR?

Answer 9

Conformation change (changes shape)

Question 10

What can bind to activated GPCR receptors?

Answer 10

G proteins

Question 11

What is the actual name of a G protein?

Answer 11

Guanine nucleotide binding protein

Question 12

What are G proteins made up of?

Answer 12

Three subunits (alpha, beta and gamma) this makes them heterotrimeric

Question 13

What happens to the G protein after it interacts with an activated GPCR?

Answer 13

The G protein itself is activated by causing GTP to exchange for GDP On the alpha subunit

Question 14

What happens to the G protein immediately after the GDP is replaced with GTP?

Answer 14

The complex dissociates into an alpha GTP and beta gamma subunit which can then interact with effector proteins

Question 15

Why do the G protein reactions occur on the plasma membrane?

Answer 15

All the substances are localised for a more efficient response

Question 16

How is the G protein signal terminated?

Answer 16

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.

Question 17

What are the 3 types of alpha subunits?

Answer 17

S (stimulates), I (inhibits) and q

Question 18

What effector is stimulated when an s subunit is activated by Adrenaline or noradrenaline?

Answer 18

Adenylyl cyclase

Question 19

What happened when adrenaline binds to a GPCR which activates an I G protein?

Answer 19

Adenylyl cyclase is inhibited

Question 20

What happened when an adrenaline or noradrenaline molecule activates a q G protein?

Answer 20

Phospholipase C is activated.

Question 21

Why can adrenaline and nor adrenaline have different affects when they bind to different GPCRs?

Answer 21

Different receptors recruit different versions of the alpha G protein subunit which causes different effects.

Question 22

What effect does the toxin CTx have?

Answer 22

Stops the snag protein subunit hydrolysing GTP into GDP, therefore the 2 subunits de not reform and remain activated.

Question 23

What does CTx stand for?

Answer 23

Cholera Toxin

Question 24

What does PTx stand for?

Answer 24

Pertussis toxin

Question 25

What effect does the toxin PTx have?

Answer 25

It prevents GDP being replaced with GTP, therefore the subunits don’t separate and so can’t become active to carry out an effect