What are the most common second messengers?

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Accepted Answer

The following table lists common second messengers and their associated pathways:

Second Messenger 
Signaling Pathway
Function(s)

Calcium
Phosphoinositol Pathway
An increase in cytosolic calcium concentrations triggers various responses such as muscle contraction, exocytosis, T lymphocyte activation, cell adhesion and apoptosis.

Cyclic adenosine monophosphate (cAMP)
cAMP or Adenylyl Cyclase Signaling Pathway
Activates protein kinase A (PKA), a cAMP-dependent kinase that phosphorylates proteins. Regulates gene transcription.

Cyclic guanosine monophosphate (cGMP)
cGMP Signaling Pathway
Activates protein kinase G (PKG), a cGMP-dependent kinase that phosphorylates proteins.

Inositol triphosphate (IP3)
Phosphoinositol Pathway
Binds to calcium channels located on the endoplasmic reticulum, trigger the release of calcium into the cytosol.

Diacylglycerol (DAG)
Phosphoinositol Pathway
Activates protein kinase C (PKC), a calcium-dependent kinase that phosphorylates proteins.

Second Messenger	Signaling Pathway	Function(s)
Calcium	Phosphoinositol Pathway	An increase in cytosolic calcium concentrations triggers various responses such as muscle contraction, exocytosis, T lymphocyte activation, cell adhesion and apoptosis.
Cyclic adenosine monophosphate (cAMP)	cAMP or Adenylyl Cyclase Signaling Pathway	Activates protein kinase A (PKA), a cAMP-dependent kinase that phosphorylates proteins. Regulates gene transcription.
Cyclic guanosine monophosphate (cGMP)	cGMP Signaling Pathway	Activates protein kinase G (PKG), a cGMP-dependent kinase that phosphorylates proteins.
Inositol triphosphate (IP3)	Phosphoinositol Pathway	Binds to calcium channels located on the endoplasmic reticulum, trigger the release of calcium into the cytosol.
Diacylglycerol (DAG)	Phosphoinositol Pathway	Activates protein kinase C (PKC), a calcium-dependent kinase that phosphorylates proteins.

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