CMB1004/L17 Regulation of Signalling Pathways

Question 1

Give 2 ways in which different cells can respond differently to the same signal.

Answer 1

By using different receptors
By activating different intracellular machinery

Question 2

How does skeletal muscle and heart muscle respond differently to ACh?

Answer 2

Skeletal - ion-channel linked receptor
Membrane depolarisation induces contraction
Heart - G-protein coupled receptor
Hyperpolarisation of membrane reduces rate of contraction

Question 3

Describe the action of NO receptors when ACh is bound. (4)

Answer 3

Conformational change
Produces cGMP
NO bound to guanylyl cyclase
Rapid relaxation of smooth muscle

Question 4

Describe the cascade of events in pancreatic acinar cells when ACh is bound. (7)

Answer 4

G-protein receptor
Phospholipase C activated
IP3 produced
Ca2+ released
Calmodulin activated
PK activated
Secretory vesicles released

Question 5

Describe the cascade of events in endothelial cells when ACh is bound. (6)

Answer 5

G-protein receptor
Phospholipase C activated
IP3 produced
Ca2+ released
Calmodulin activated
NO synthase activated

Question 6

Describe a stable signalling complex.

Answer 6

Components of the signalling pathway are linked by a scaffold protein

Question 7

Describe a transient signalling complex.

Answer 7

Signalling complex assembles after the receptor is activated
OR
Modification of plasma phospholipid molecules

Question 8

Give 4 ways in which a signal can be switched off.

Answer 8

Removal/inactivation of signal
Removal/inactivation of receptor
Inactivation of activated signalling proteins
Degradation/removal of second messengers

Question 9

How do many drugs work to start/stop signalling pathways?

Answer 9

Blocking or enhancing the ‘switching off’ process

Question 10

Give 3 ways in which the signal can be removed from a pathway.

Answer 10

Degradation
Recycling of signalling molecule
Sequestration by other proteins

Question 11

What is a common mechanism of receptor removal?

Answer 11

Ligand-dependent receptor-mediated endocytosis

Question 12

Give 3 methods of inactivation of activated signalling proteins.

Answer 12

GTP hydrolysis
(De)phosphorylation
Allosteric control

Question 13

Describe how cholera toxin interferes with G-protein hydrolysis. (4)

Answer 13

ADP-ribosylation of Galpha prevents hydrolysis of GTP
Locks G-protein in active site
Adenylyl cyclase remains activated
Increase in cAMP leads to loss of Cl- and H2O into intestinal lumen

Question 14

Describe how allosteric inactivation stops a pathway.

Answer 14

Dissociation from activator or association with inhibitor

Question 15

Give an example of removal of second messengers.

Answer 15

Removal of cAMP and cGMP by hydrolysis
Catalysed by phosphodiesterase

Question 16

Give an example of a drug which inhibits cGMP phosphodiesterase.

Answer 16

Viagra

Question 17

What kind of inhibition is involved in Viagra?

Answer 17

Competitive inhibition