Signalling Between Cells 2

Question 1

How does an inotropic receptor function?

Answer 1

ligand binds to receptor, conformational change to open pore, movement of ions allowed

Question 2

Give 2 examples of inotropic receptors

Answer 2

1) nicotinic acetylcholine
ligand = ACh location = skeletal muscle effect = contraction
2) GABA
ligand = GABA location = neurone effect = decreased neuronal activity

Question 3

What are the subunits of G protein

Answer 3

alpha and beta

Question 4

How is signal transduction carried out for G protein couple receptor?

Answer 4

7-TM receptor and heterotrimeric G protein are inactive
ligand binds and conformation change to receptor
unassociated G protein bids to receptor
the GDP molecule bound to the G protein is phosphorylated to GTP
G protein dissociates into two active components:
-alpha sub unit (with GTP)
-beta-gamma sub unit
these bind to their target proteins
internal GTPase activity on alpha subunit dephosphorylates GTP to GDP
alpha subunit dissociates from target protein and is inactive bind back with beta-gamma

Question 5

Name the G alpha subunit types and give an example of each

Answer 5

Gs protein linked receptor
e.g. beta1 adrenergic receptor to increase HR
Gi protein linked receptor
e.g. M2 muscarinic receptor to decrease HR
Gq protein linkes receptor
e.g. A!-1 angiotensin receptor for vasoconstriction

Question 6

How does Gs protein linked receptor work?

Answer 6

stimulates adenyl cyclase by converting ATP to cAMP which activates PKA

Question 7

How does Gi protein linked receptor work?

Answer 7

inhibits adenyl cyclase by lowering levels of PKA

Question 8

How does Gq protein linked receptor work?

Answer 8

stimulates phospholipase C by converting PIP2 to IP3 and DA, IP3 stimulates Ca2+ release and DAG activates PKC

Question 9

How does an enzyme linked receptor work?

Answer 9

ligand binding causes receptors to cluster which activates enzyme activity in cytoplasmic domain
enzymes phosphorylate the receptor which causes binding of signalling proteins to cytoplasmic domain
signalling proteins recruit others and generate signal

Question 10

Give 2 examples of enzyme linked receptors for tyrosine kinase

Answer 10

insulin receptor (CD220 antigen)
ligand = insulin 
effect = glucose uptake
ErbB receptor
ligand = epidermal growth factor and transforming growth factor beta 
effect = cell growth and proliferation

Question 11

How does a cytoplasmic receptor work?

Answer 11

located in cytosolic compartment and is associated with chaperone molecules (hsp)
hormone binds to receptor and hsp dissociates
2 hormone bound receptors form a homodimer which translates to nucleus and binds to DNA

Question 12

How does a nuclear receptor work?

Answer 12

located in nucleus

binding of hormone ligand causes transcriptional regulation

Question 13

Give an example of a cytoplasmic receptor

Answer 13

glucocorticoid receptor
ligand = cortisol and corticosterone
effect = decreased immune response and increased gluconeogensis

Question 14

Give an example of a nuclear receptor

Answer 14

thyroid hormone receptor
ligand = T4/T3
effect = growth and development