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cyclase is no longer stimulated by Gs -cAMP phosphodiesterase breaks down the cAMP, decreasing its concentration -PKA no longer active -Glycogen synthesis stimulated, lowering glucose and slowing glycolysis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