Download JULY 2007 QUESTION 13 Describe the term

JULY 2007
QUESTION 13
Describe the term second messenger. Give an example of a drug
which manifests its action via a second messenger
Second Messengers are a component of the signal transduction cascade which occurs following the combination of a receptor and an agonist (drug or hormone)
response is
activated and
effector released
agonist binds
to receptor
second messenger
causes intracellular
event
effector acts on
second messenger
Second messengers systems usually act via phosphorylation and provide
amplification (increasing responses and continuing effect after dissociation of drug-receptor)
flexibility (they provide branch points in signalling pathways enabling more variability)
Types of second messengers include;
Calcium and Inositol 1,4,5 triphosphate (IP3)
Noradrenaline at alpha 1 receptors (GqPCR) increase IP3 and Calcium
Causing smooth muscle contraction
Cyclic Guanosine MonoPhosphate cGMP
Nitric Oxide, ANP
Cyclic Adenosine MonoPhosphate cAMP
Drug example is salbutamol (beta adrenergic amine) - others glucagon, histamine, 5-HT
Mechanism shown below
Gs Protien Coupled Receptor - Salbutamol
Adenylyl Cyclase is an effector
g B
Activation of the G-Protien
causes the alpha subunit
to drop the GDP for GTP,
seperate and travel to
GDP
adenylyl cyclase
Christopher Andersen 2012
a
a
ATP
cAMP
GTP
GTP
Biological Response