Signalling between cells II

Question 1

Give two examples of ionotropic receptors.

Answer 1

Nicotinic Acetylcholine Receptor

GABAA Receptor

Question 2

Explain how GABAA receptors work.

Answer 2

Located on many cells in the CNS
Allows transmission of anions
GABA binds to the GABA receptor making it open
Cl- influx
GABA causes a depression of activity
Blocking GABA receptors leads to hyperexcitability of the CNS

Question 3

Describe the activation process of a G-protein coupled receptor

Answer 3

The ligand binds and changes conformation of the receptor
The G protein heterotrimer binds to the intracellular compartment (it has a GDP bound to it)
The GDP is exchanged for a GTP
GTP allows the dissociation of the alpha subunit and the beta-gamma subunit
Subunits go and bind to target proteins
Once the alpha subunit has fulfilled its function, the GTP is dephosphorylated (by internal GTPase activity) to GDP allowing the alpha subunit to dissociate from the target protein and reform the heterotrimer with GDP attached

Question 4

What are two other names for G-protein coupled receptors?

Answer 4

7-TM Receptor Serpentine Recepto

Question 5

What are the three types of G-protein linked receptor and how do they differ?

Answer 5

Gs Gi and Gq

They differ in the alpha subunit

Question 6

Describe the action of Gs-protein linked receptors.

Answer 6

Stimulates adenylate cyclase
Adenylate cyclase converts ATP –> cAMP
cAMP increases levels of protein kinase A

Question 7

Give an example of a Gs-protein linked receptor.

Answer 7

Beta-1-adrenergic receptor

Question 8

Describe the action of Gi-protein linked receptors.

Answer 8

Has the opposite effect to Gs protein linked receptors Inhibits adenylate cyclase

Question 9

Give an example of a Gi-protein linked receptor.

Answer 9

M2-muscarinic receptor

Question 10

Describe the action of Gq-protein linked receptors.

Answer 10

Activates Phospholipase C
PLC converts PIP3 to IP3 and DAG
IP3 increases intracellular Ca2+
DAG activates Protein Kinase C

Question 11

Give an example of a Gq-protein linked receptor.

Answer 11

AT-1 angiotensin receptor

Question 12

Describe the action of enzyme-linked receptors.

Answer 12

The ligand binds to the receptors leading to receptor clustering
The clustering of receptors leads to activation of intracellular enzymes, which leads to several chemical cascades
The receptors are linked to kinases

Question 13

What are the three types of enzyme-linked receptor?

Answer 13

Tyrosine Kinase (95%)
Guanylyl-Cyclase
Serine-Threonine Kinase

Question 14

Give two examples of enzyme-linked receptors.

Answer 14

Insulin Receptor ErbB

Receptor

Question 15

Describe the action of Type 1 Intracellular Receptors

Answer 15

Intracellular receptors are bound to heatshock proteins and are found in the cytoplasm
Ligands (usually steroids) pass through the membrane and bind to the receptor
Receptor dissociates from heatshock protein
The receptor and ligand together move into the nucleus and bind to the DNA and causes increased or decreased transcription
These receptors function as homodimers

Question 16

Describe the action of Type 2 Intracellular Receptors

Answer 16

These are present in the nucleus and are already bound to the DNA
The ligand passes through the membrane and through the nuclear envelope and binds to the receptor causing changes in transcription

Question 17

Give an example of a Type 1 Intracellular Receptor. State its ligands, physiological effects and agonists

Answer 17

Glucocorticoid receptor
Cortisol, Corticosterone
Physiological effect: Downregulate immune response, increase gluconeogenesis
Agonist: Glucocorticoids

Question 18

Give an example of a Type 2 Intracellular Receptor. State its ligands, physiological effects and agonists.

Answer 18

Thyroid Hormone Receptor
Ligands: Thyroxine, Triiodothyronine
Physiological Effect: Growth and Development
Agonist: Thyroid Hormones