G proteins
protein Gs which stimulates the enzyme adenylate cyclase.
Activated adenylate cyclase takes adenosine triphosphate or ATP, and removes two phosphate molecules transforming it into cyclic adenosine monophosphate or cAMP.
cAMP moves throughout the cytoplasm and binds to the enzyme protein kinase A.
Protein kinase A has two parts - a regulatory subunit and a catalytic subunit, and cAMP specifically binds the regulatory subunit of protein kinase A.
When cAMP binds it makes the regulatory subunit dissociate from the catalytic subunit of protein kinase A.
It’s like pulling the pin out of the fire extinguisher allowing it, in this case the catalytic subunit, to do its job.
So after dissociating, the catalytic subunit of protein kinase A is free to phosphorylate target proteins that trigger a cellular response.
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