Chapter 13: Signal Transduction Pathways Flashcards
Signal transduction is critical because…
Allows organism to sense its environment and formulate a biochemical response
5 Steps of the Signal transduction pathway
- Release of a primary message
- Reception
- Relay - secondary messengers
- Activation
- Termination
A low [] of signal in the environment (outside) can yield a…..
Large intracellular signal and response (inside)
What are the 3 major classes of membrane receptors?
- Seven-transmembrane helix (7TM) receptors associated with heterotrimeric G-proteins
- Dimeric membrane receptors that recruit protein kinases
- Dimeric protein receptors that are protein kinases (both receptor and kinase functions)
The most common receptors in signaling events are?
7TM receptors have a host of functions!
They mediate hormone action, secretion, neurotransmission, chemotaxis, exocytosis, control of blood pressure, embyrogenesis, cell growth, development, smell, taste, vision, viral infection
Several thousand 7TM receptors exist. What % of currently used drugs target these receptors?
50%
7TM receptors have _________ and ___________.
Seven alpha-helices and span the membrane bilayer
Ligand epinephrine receptor binds to B-adrenergic receptor. What happens? Why?
Change in conformation to allow the signal to be able to be detected inside the cell
The unactivated G-protein is a heterotrimer consisting of…
An alpha subunit, bound to GDP and beta and gamma subunits.
After binding epinephrine, the beta-adrenergic receptor activates a…
Heterotrimeric G-preitein
*NOTE: One receptor can stimulate many G-proteins*
Once G-protein is activated, the alpha subunit exchanges…
GDP (low energy state) for GTP
The exchanged GTP bound alpha-subunit transmits the signal to other cellular components which…
Gives an amplified response/keeps amplifying the signal
The activated G-protein will then stimulate…
Adenylate cyclase
Activation of adenylate cyclase leads to…
Synthesis of cAMP
Binding of epinephrine to the receptor on the cell surface _______ the rate of cAMP production in the cell.
Increases
cAMP stimulates phosphorylation of many target proteins, including…
Protein Kinase A which controls many responses (GIT, blood, skin, etc.)
Protein Kinase A (PKA) has…
2 regulatory subunits and 2 catalytic components
Binding of cAMP dissociates which subunits of the PKA?
R subunits
How do you turn this epinephrine signal off? (3 ways)
- G alpha has ability to reset itself by cleaving the bound GTP to GDP to terminate the G-protein
- cAMP phosphodiesterase converts cAMP to AMP which prevents activation of PKA
- The epinephrine-beta-adrenergic receptor is reversible. Dissociates/resets
What is Cholera?
Produces a toxin that modifies one specific G-protein and locks it in the active form. Net result is a loss of NaCl and water into the intestine
*Severe diarrhea that can kill you within 24 hours
Pertussis Toxin (Whooping Cough)
Modifies a G-protein by trapping it in the inactive form so you cannot turn on a signaling pathway so it is rendered inactive
Hydrolysis of Phosphatidylinositol Biphosphate by Phospholipase C generates 2 secondary messengers
DAG and IP3
Binding of IP3 in the ER causes what? What is an example of this pathway?
Release of Ca2+ out of the ER and raise how much calcium is present in the cytoplasm
Ex: Vasopressin binding to a 7TM
DAG with calcium activates…
Protein kinase C
