cAMP second messenger system (w/ epinephrine)
to increase cAMP...
stimulate adenylate cyclase or inhibit phosphodiesterase
glycogen phosphorylase kinase
stimulates glycogen phosphorylase to break down glycogen to glucose
Step 6: when epinephrine is no longer bound to receptor (5 things)
-Gs inactivates and remains inactive -adenylate cyclase is no longer stimulated by Gs -cAMP phosphodiesterase breaks down the cAMP, decreasing its concentration -PKA no longer active -Glycogen synthesis stimulated, lowering glucose and slowing glycolysis
Catalytic subunits
-binding of cAMP to the regulatory subunits causes release of catalytic subunits. -free catalytic subunits are active, proceed to phosphorylate proteins
cAMP phosphodiesterase
-breaks cAMP down to AMP -always active at a constant rate
Adenylate cyclase
-makes cAMP from ATP -stimulated by Gs -inhibited by Gi
4 things the cAMP system accomplishes
1. getting message into cell 2. cascade amplification 3. coordinated response 4. response ends when first message is gone
Step 3:
Activation of Gs causes cytoplasmic cAMP to increase
Step 1:
Epinephrine binds to its receptor on the surface of muscle cell (b-adrenergic receptor linked to Gs-protein)
Step 5:
PKA phosphorylates several different types of enzymes (glycogen phosphorylase kinase and glycogen synthase)
Step 2:
The Gs-Protein activates adenylate cyclase.
Step 4:
cAMP acts as an allosteric modulator, stimulating a cAMP dependent protein kinase known as PKA
type of curve on a graph
cAMP makes an S-curve on the graph
To increase the number of phosphorylated proteins in the cell...
decrease activity of cAMP phosphodiesterase
to decrease cAMP...
inhibit adenylate cyclase or stimulate phosphodiesterase
glycogen synthase
inhibited to by being phosphorylated
PKA two catalytic subunits
perform the protein kinase reaction, and two regulatory subunits
If the cAMP falls...
the regulatory subunits release the cAMP and bind back to the catalytic subunits, stopping their activity
The allosteric effect of Gs
will last a short time, because of the GTPase activity of Gs