Signal transduction GCPR and RTK

Question 1

What is the physical composition of GCPR

Answer 1

Has 7 transmembrane alpha helices with an extracellular binding site and intracellularly, it has an alpha, beta, gamma G protein.

Question 2

What si the inactive version of the G protein

Answer 2

GDP bound Alpha subunit

Question 3

What are the types of GCPR and what do they do

Answer 3

Gs,Gi,Gq
G stimulatory
G inhibitory
G q

Question 4

What is the signalling pathway for G proteins

Answer 4

• A molecule will bind to the receptor on the GCPR
• This will cause a conformational change in shape in the GCPR
• GDP on the alpha subunit is exchanged for GDP activating the alpha subunit and causing it to dissociate from the beta, gamma dimmer.
• GTP alpha subunit activates adenylate cyclase which converters ATP to cAMP
• cAMP then activates protein kinase which goes on and has a secondary messenger effect

Question 5

What is the difference between Gs and Gi GCPR

Answer 5

Gs is stimulatory and Gi is inhibitory and so Gi will stop the activation of adenylate cyclase and thus preventing the conversion ATP to cAMP and thus preventing the activation of Protein Kinase.

Question 6

What is the signalling pathway involved in Gq

Answer 6

• A molecule will bind to the receptor on the GCPR
• This will cause a conformational change in shape in the GCPR
• GDP on the alpha subunit is exchanged for GDP activating the alpha subunit and causing it to dissociate from the beta, gamma dimmer.
• GTP bound alpha subunit will activate phospholipase C which which converts PIP2to IPC and DAG.
  IPC causes a the neoplasm in reticulum to produce more CA2+ and the DAG activates Protein Kinase c.
  This produces a 2nd art messenger model.

Question 7

What is the signalling pathway involved in RTK (receptor tyrosine Kinase)

Answer 7

• Growth factors bind to the top of the the RTK
• this activates the RTK and cause dimerisation ( the 2 receptors to link up).
• this causes cross phosphorylation between the RTK ( one RTK will phosphorylate the tyrosine on the other RTK)
• this results in a phosphorylate SH2 domain which allows for various enzymes to bind.
• when an enzyme binds to SH2 domains, GDP on the RAS on the RTK is exchanged for GTP activating the RAS beginning a cascade reaction where the amount of activators will determine the product
• MAP - kinase, kinase, kinase = RAF
• MAP - kinase, kinase = MEK
• MAP - kinase = ERK