Cell Signaling - G protein pathway, Transduction

Question 1

Explain the events that follow when a signal molecule (hydrophilic) binds to a G protein coupled receptor

Answer 1

1. the signal molecule binds to the GPCR on the cell membrane
2. the activated receptor interacts with a G protein, causing the G protein to exchange GDP for GTP, activating the G protein
3. the activated G protein undergoes a change, leading to the separation of its subunits
4. the activated alpha subunit binds to and regulates the activity of an effector molecule with the cell
5. the effector, in turn generates second messengers within the cell
6. these messengers activate or inhibit various cellular processes that lead to a specific response
   7.the G protein’s GTP causes GTP hydrolysis to GDP leading to the inactivation of the G protein

Question 2

What is the role of second messengers in signal transduction?

Answer 2

second messengers play a crucial role in signal transduction by transmitting signals from the cell membrane, where a signaling molecule binds to the cellular interior

Question 3

Explain the process which uses cAMP and phosphorylation cascade.

Answer 3

1. a signaling molecule binds to its receptor on the cell membrane, typically a GPCR
2. the activated receptor stimulates a G protein, leading to the activation of adenylyl cyclase (enzyme)
3. adenylyl cyclase converts ATP into cAMP which serves as a second messenger
4. cAMP activates protein kinase by binding to its subunits, causing the catalytic subunit to be released and activated
5. activate protein kinase’s catalytic subunits target proteins within the cell which sets off a phosphorylation cascade, where each protein activates the next protein
   6.this can lead to various cellular responses
6. the signal is terminated by: degradation of cAMP by phosphodiesterase; dephosphorylation of phosphorylated proteins

Question 4

State the function of the following enzymes: kinase, phosphatase, adenylyl cyclase, phosphodiesterase

Answer 4

kinase - catalyze the transfer of a phosphate group from ATP to a substrate molecule (activates or deactivates the substrate)
phosphatase - remove phosphate groups from substrates (can activate or deactivate proteins)
adenylyl cyclase - converts ATP to cAMP
phosphodiesterase - break down cAMP to AMP

Question 5

What is signaling transduction?

Answer 5

process by which cells communicate and respond to external signals or stimuli