Final answer:
PKA, or protein kinase A, is activated by binding to cAMP. One example of a fast response done by activated PKA is the fight-or-flight response to adrenaline.
Step-by-step explanation:
PKA, or protein kinase A, is activated by binding to cAMP, which is a second messenger molecule. One example of a fast response done by activated PKA is the fight-or-flight response to adrenaline. When adrenaline binds to its receptors, G-proteins activate adenylate cyclase, which produces cAMP. cAMP then binds to and activates PKA, initiating a phosphorylation amplification cascade. This cascade leads to various cellular responses, such as the breakdown of glycogen to release glucose for energy.