Lecture 20

Question 1

Signal Transduction Pathways

Answer 1

• Pleiotropic responses to an extracellular stimulus that are transducer through the plasma membrane
• each pathway starts with an impermeable hydrophillic first messenger that is converted into a second messenger through an effector enzyme-propagating the signal throughout the intracellular enviroment

Question 2

GPCR

Answer 2

G-protein coupled receptors
specific for:
-odorants(smell)
-photons (vision)
-neurotransmitters
-Hormones
-Calcium

Question 3

G proteins

Answer 3

• signal transducer
• has three subunits-> alpha, beta, and gamma
• alpha and gamma are lipid-anchored membrane proteins (FA and prenyl)
• G protein is inactive when it is bound to GDP

Question 4

How is the G-GDP complex activated? and describe the process?

Answer 4

activation occurs when the complex runs into a hormone receptor complex:

• displacement of GDP with GTP
• Conformational change in alpha subunit
• dissociation of Beta and Gamma subunits
• G-GTP is functional active with regards to signal propagation

Question 5

How does the G protein recycle

Answer 5

-the GTP is spontaneously hydrolyzed and the G protein reverts to the G-GDP state and associates with beta and gamma subunits and is ready for another cycle