Describe the term second messenger.
Give an example of a drug that manifests its action via a second messenger.
Second messenger-Hormone/drug - receptor binding is coupled to a subsequent series of
intracellular biochemical events that precipitate the ultimate hormone/drug effect.
Examples are G proteins an energy dependent process by which there is hydrolysis of G
protein-associated GTP to GDP. There are both stimulating and inhibitory proteins
which subsequently act to increase or decrease activity of the enzyme adenylyl cyclase,
resulting in increased levels of cyclic adenosine 3 ',5'-monophosphate ( cAMP) in the cell
which in turn activates protein kinases that phosphorylate various proteins, ion channels, and second messenger enzymes. Also G proteins stimulate hydrolysis of phosphatidyl-inositol-4,5-bisphosphate (PIP2) generating inositol-1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol (DAG). Both systems increase intracellular calcium.
The college answer leaves much to be desired.
According to one of the (many) definitions, a second messenger is
"...any of various intracellular chemical substances...that transmit and amplify the messages delivered by a first messenger to specific receptors on the cell surface"
The basic characteristics of a second messenger system are as follows:
A good all-purpose example is the β-1 adrenergic receptor. Wheeler (2005) gives a good overview, in case the need for one ever comes up
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