Chemical Synaptic Transmission SEM1

Question 1

What are G protein-coupled receptors

Answer 1

Metabotropic

Question 2

What are properties of G protein coupled receptors (GPCR)

Answer 2

7 transmembrane domain structure
N-terminus is extracellular
C-terminus is intracellular

Question 3

What are features of the structure of G proteins

Answer 3

Heterotrimeric proteins - 3 non-identical subunits α, β, γ

Question 4

What are the key steps of g protein function/activation

Answer 4

1)receptor activation
2)G protein activation
3)G protein subunit dissociation
4)signal amplification
5)termination of signal

Question 5

What state is the G protein in initially

Answer 5

Inactive state with GDP bound to its α (alpha) subunit

Question 6

How is the G protein activated

Answer 6

Agonist binding to GPCR induces conformational change in receptor which activates the G protein by exchanging GDP for GTP on the α (alpha) subunit

Question 7

What causes the dissociation of subunits during G protein activation

Answer 7

In the active form of G protein the α subunit dissociates from the β γ subunits which can now activate or inhibit effector proteins

Question 8

How is signal termination induced in G protein signalling mechanism

Answer 8

The α subunit has GTPase activity which removes a phosphate group by hydrolysis from GTP to GDP -> allows G protein to revert to inactive form α and β γ subunits as a trimer

Question 9

What is a feature of M1 receptors

Answer 9

Neural (slow EPSP in ganglia)

Question 10

What is a feature of M2 receptors

Answer 10

Cardiac area of function

Question 11

What do M3 receptors target

Answer 11

Glandular secretion
Contraction of visceral smooth muscle
Vascular relaxation

Question 12

What is the process of receptor activation with the action of acetylcholine (Ach) on the hearts muscarinic M2 receptors

Answer 12

Ach binds to muscarinic M2 receptors on the cardiac muscle cells - receptors coupled with G proteins

Question 13

What is the process of G protein activation with the action of acetylcholine on the hearts M2 receptors

Answer 13

After activation of Ach, the G protein associates with the M2 receptor dissociates into α and β γ

Question 14

What is the effect on potassium channels with the action of acetylcholine on the hearts M2 receptors

Answer 14

The β γ subunits directly interact with and open the K+ channels in the heart cell membranes

Question 15

What is the cellular effect with the action of acetylcholine on the hearts M2 receptors

Answer 15

The opening of K+ channels allows potassium ions to flow out of cell this efflux of K+ leads to hyperpolarisation of cardiac muscle cell membranes

Question 16

What is the physiological response with the action of acetylcholine on the hearts M2 receptors

Answer 16

Contributes to parasympathetic slowing of heart rate (bradycardia) by:
Shortening duration of cardiac action potential
Increasing interval between cardiac action potentials