Biochemical Signaling: Pathways Flashcards
What does 7TM stand for?
Seven-transmembrane-helix receptors
What are the three most common types of membrane receptors that mediate information transfer into the cell?
1) Seven-transmembrane-helix receptors
2) Dimeric membrane receptors that recruit protein kinases
3) Dimeric protein receptors that are protein kinases
What is the largest class membrane receptors?
7TM
About what percentage of drugs in use alter 7TM receptors?
50%
What is the structure of 7TM receptors?
Seven helices spanning the membrane bilayer.
How do 7TM receptors work?
Binding of ligand on the part of the receptor outside of the cell induces a conformational change detectable within the cell.
What type of receptor is a beta-adrenergic receptor? What does it bind?
Seven-transmembrane-helix receptor (7TM); it binds epinephrine (also called adrenaline)
What receptor binds epinephrine? What kind of receptor is it?
beta-adrenergic receptor; 7TM
What does ligand binding to 7TM receptors lead to?
Conformational changes in the cytoplasmic domain of the receptor, leading to activation of a heterotrimeric GTP-binding protein (G protein).
What does an unactivated G-protein consist of?
1) An alpha subunit bound to GDP (most important)
2) A beta subunit
3) A gamma subunit
Why is an unactivated G-protein a heterotrimer?
It consists of three different subunits
What happens when a G-protein is activated?
1) GDP is exchanged for GTP
2) The alpha subunit dissociates from the beta and gamma subunits, forming G-alpha and G-beta, gamma units.
3) This dissociation transmits the signal that the ligand has bound to the receptor.
What does the “G” in G-protein stand for?
guanyl nucleotide
True or false: A single hormone-receptor complex can stimulate nucleotide exchange in only one G-protein heterotrimer.
False; It can stimulate nucleotide exchange in many G-protein heterotrimers, giving an amplified response.
What does the activated G protein do?
Stimulates activity of adenylate cyclase, a second messenger that increases the concentration of cAMP
What enzyme increases cyclic AMP by forming it from ATP?
adenylate cyclase
What does GPCR stand for?
G-protein coupled receptors
What does the effect of the increased concentration of cyclic AMP in the cell depend on?
The type of cell involved.
What are most effects of increasing the concentration of cAMP mediated by?
The activation of a protein kinase (an enzyme).
What enzymes phosphorylate a substrate at the expense of a molecule of ATP?
kinases
What does PKA stand for?
Protein kinase A
What does PKA consist of?
2 regulatory (R) chains and 2 catalytic (C) chains
What activates the R2C2 complex of protein kinase A?
cyclic AMP
Which chains of PKA does cAMP bind to?
The 2 regulatory chains
What happens when cAMP binds to the regulatory chains of PKA?
The 2 catalytic chains are released,
What does activated PKA do?
Phosphorylates specific serine and threonine residues in many target proteins, altering their activity.
What turns off the cAMP cascade?
cAMP phosphodiesterase
How does cAMP phosphodiesterase turn off the cAMP cascade?
It converts cAMP into AMP, which does not activate PKA.
What happens after the cAMP cascade is turned off by cAMP phosphodiesterase?
The C and R subunits of PKA rejoin to form the inactive enzyme.
How is the signal initiated by 7TM receptors switched off?
G-alpha subunits have intrinsic GTPase activity that hydrolyzes the bound GTP to GDP and Pi (inorganic orthophosphate) and thereby deactivates itself.
What happens as hormone concentration decreases?
The hormone dissociates from the receptor and the receptor returns to its initial unactivated form.
True or false: Ligand-receptor interaction is reversible.
True
True or false: The bound GTP on G alpha acts as a built in clock that spontaneously resets the G alpha subunit after a short period of time.
True
What does the likelihood of a receptor remaining in an inactive state depend on?
The concentration of hormone in its environment.
What are cholera and whooping cough due to?
Altered G-protein activity
What is the bacterial toxin that causes cholera?
Choleragen
What is the result of choleragen infection?
Choleragen modifies the G-alpha-s (s=stimulatory) protein so that it is trapped in the active GTP-bound form. This causes loss of NaCl and water into the intestine (causes cholera).
What is the result of pertussis infection?
Pertussis modifies the G-alphai (I=inactive) protein, trapping it in the inactive form, rendering it inactive (causes whooping cough)
What does the hormone vasopressin regulate?
water retention
What does PIP2 stand for? What is it?
Phosphatidylinositol 4, 5-bisphosphate; a phospholipid present in cell membranes.