Tissues 9 (Signalling between cells)

Question 1

What are two examples of ionotropic receptors?

Answer 1

• Nicotinic Acetylcholine Receptor

- GABAA Receptor

Question 2

How do GABAA receptors work?

Answer 2

• Located on many cells in the CNS
• Allows transmission of anions
• GABA binds to 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

• ligand binds and changes conformation of the receptor
• unassociated g-protein binds to receptor
• GDP bound is exchanged for a GTP
• GTP allows the dissociation of the α & βγ subunits that bind to target proteins
• Once α subunits function is fulfilled, GTP–>GDP by GTPase, allowing subunit to dissociate
• heterotrimer reformed with GDP attached

Question 4

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

Answer 4

• 7-TM Receptor

- Serpentine Receptor

Question 5

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

Answer 5

• Gs
• Gi
• Gq
• differ in the alpha subunit

Question 6

What is 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

What is an example of a Gs-protein linked receptor?

Answer 7

• Beta-1-adrenergic receptor

- increases heart rate

Question 8

What is the action of Gi-protein linked receptors.

Answer 8

• opposite effect to Gs protein linked receptors

- inhibits adenylate cyclase

Question 9

What is an example of a Gi-protein linked receptor?

Answer 9

• M2-muscarinic receptor

- decreases heart rate

Question 10

What is 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

What is an example of a Gq-protein linked receptor?

Answer 11

• AT-1 angiotensin receptor

- causes vasoconstriction

Question 12

What is the action of enzyme-linked receptors?

Answer 12

• ligand binding causes receptor clustering
• intracellular enzymes activated
• enzymes phosphorylate receptor causing signalling protein binding to cytoplasmic domain
• other proteins recruited & signal generated in cell
• receptors linked to kinases

Question 13

What are the three types of enzyme-linked receptor?

Answer 13

• Tyrosine Kinase (95% - glucose uptake)
• Guanylyl-Cyclase (vasodilation)
• Serine-Threonine Kinase (apoptosis)

Question 14

What is an example of enzyme-linked receptors?

Answer 14

• Insulin Receptor (CD220 antigen)

Question 15

What is the action of Type 1 Intracellular Receptors?

Answer 15

• chaperone (heatshock) molecules in cytosolic compartment
• Ligands (usually steroids) binds to the receptor
• Receptor dissociates from heatshock protein
• homodimer translocated to nucleus & binds to DNA
• transcription increased or decreased

Question 16

Describe the action of Type 2 Intracellular Receptors

Answer 16

• ligand passes through the membrane and through the nuclear envelope
• ligand binds to the receptor causing changes in transcription

Question 17

What is an example of a Type 1 Intracellular Receptor?

Answer 17

• Glucocorticoid receptor
• ligands: Cortisol, Corticosterone
• decreases immune response, increases gluconeogenesis
• Agonist: Glucocorticoids

Question 18

What is an example of a Type 2 Intracellular Receptor?

Answer 18

• Thyroid Hormone Receptor
• Ligands: T3 & T4
• causes Growth and Development
• Agonist: Thyroid Hormones

Question 19

What are the four types of intracellular signalling?

Answer 19

• ionotropic receptor
• g-protein coupled receptor
• enzyme-linked receptor
• intracellular receptor

Question 20

What is a homodimer?

Answer 20

2 hormone bound receptors

Question 21

Where do type 1 intracellular receptors operate?

Answer 21

cytoplasm

Question 22

Where do type 2 intracellular receptors operate?

Answer 22

nucleus