Biochemistry Ch. 13-Signaling Pathways

Steps of signal circuits

1. release of primary messenger

2. reception of the primary messenger

3. relay of information by the second messenger

4. activation of effectors that directly alter physiological response

5. termination of the signal

Seven-Transmembrane-Helix receptors

change conformation in response to ligand binding and activate G-proteins

Also called G-protein coupled receptors (G-PCRs).

Activation of G-protiens

GDP breaks off from the beta and gamma parts, turning into GTP, this turns ATP into cAMP, activating protein kinase A

GTP hydrolysis

G proteins spontaneously reset (bind to their beta and gamma parts)

Deactivated receptors 

the likelihood that the receptor remains in its unbound state depends on the concentration of ligand in the environment

Phospholipase C

hydrolyses PIP2 into DAG and IP3, secondary messengers

DAG is bound to the membrane and stays, IP3 is the messenger in the cell

IP3

binds to channels on the ER that release Ca stores

DAG

activated protein kinase C 

Dimerization of signals

receptor binds (dimerization), proteins come together and phosphorylates each other, activates the kinases

Calmodulin (CaM)

four Ca binding sites, activated by the binding of Ca when cytoplasmic calcium levels are raised