GCPRs And Intracellular Signalling

Question 1

What second messangers do Gs proteins active?

Answer 1

CAMP

This then goes on to active PKA

Question 2

What second messangers do Gi activate?

Answer 2

Inhibit the activity of Ac,

• reduce the amount of cAMP
• no production of PKA
• target proteins not phosphorylated

Question 3

What second messangers do Gq proteins activate?

Answer 3

Activate phospholipase C

• cleaves PIP2 into IP3 and DAG
• IP3 binds to receptors on ER and increases cytoplasm Ca
• DAG can have simular effects to PKA

Question 4

What is signal amplification?

Answer 4

A small change in stimulus causing a larger cellular response

Question 5

What is the importance of amplification?

Answer 5

Allows a small stimulus to rapidly produce a phisiological change.
Only need small levels ligands to bind

Question 6

What is an example of a signalling cascade?

Answer 6

Ligand- Gprotien- AC- many cAMP- many PKA - many more target proteins

Question 7

What does intracellular Ca changes regulate?

Answer 7

Muscle contraction 
Realease of neurotransmitters 
Ferlilization 
Cell death 
Regualtion of metabolism 
Learning and memory

Question 8

How is intracellular Ca levels increased?

Answer 8

Across plama membrane (influx)

• Ligand gated channels
• VOCC

From ER stores (realse)

• IP3 receptors (IP3 binding)
• Ca induced Ca release receptors

Question 9

How are Ca concentrations maintained/ reduced?

Answer 9

Efflux out of cell:

• Plama memb ATPase (PMCA)
• Na/Ca exchanger (Na down conc grad (in) so Ca against grad (out)

Uptake into ER:
-SR/ER Ca ATPase (into lumen of ER)

Question 10

How does cholera toxin interfere with G protein function?

Answer 10

Covalrntly modifies GaS

By preventing apha GTP becoming inactive
Prevents GTP-GDP hydrolysis

Chronially on (stops termintaion of Gs signalling)

Question 11

How does the pertussis toxin interfere with G protein signalling?

Answer 11

Uncouples Gi prefering GPCRs

Prevents GTP-GDP exchange, so protein cant become active.

Covalently modifies Gai

Gi signalling chronically off