1. Specific signal transduction mechanisms
adenosine-3’,5’-cyclic monophosphate (cAMP)
guanosine-3’,5’-cyclic monophosphate (cGMP)
inositol triphosphate (IP3) & Ca2+
diacylglycerol (DAG)
calmodulin
steroid receptors – transcription factors

2. cAMP schematic + adenylate cyclase    Mg.ATP
A.C 
Mg.ATP
inactive protein kinase +
inactive protein
cAMP
kinase
PKA
modulation of protein activity by
active protein
kinase
cAMP
PKA
phosphodiesterase
PHOSPHORYLATION
5’AMP
CELLULAR RESPONSE

3. Important points
cAMP is formed from Mg.ATP by the action of the enzyme adenylate cyclase
cAMP stimulates the formation of activated cAMP-dependent kinase (PKA)
PKA exerts its effects by phosphorylation of specific proteins
cAMP is inactivated by being converted to 5’AMP by the action of cAMP phosphodiesterase

4. Specific Example
adenylate cyclase can be STIMULATED or INHIBITED by activating different RECEPTORS Gi Gs
A.C - +
INHIBITORY
STIMULATORY
RECEPTOR / AGONIST
RECEPTOR / AGONIST
eg ADENOSINE
ACTING VIA A2
eg ADENOSINE
ACTING VIA A1