Final answer:
When intracellular cyclic AMP (cAMP) levels rise, it activates protein kinases that transfer a phosphate group to substrate molecules, leading to changes in cellular processes. This activation occurs when a hormone binds to its receptor, activating a cascade that ultimately results in gene transcription.
Step-by-step explanation:
When intracellular cyclic AMP (cAMP) levels rise, it activates a group of proteins called protein kinases. These protein kinases transfer a phosphate group from ATP to a substrate molecule, a process known as phosphorylation. This phosphorylation changes the structural orientation of the substrate molecule, activating it and allowing it to mediate changes in cellular processes.
An increase in intracellular cAMP can occur when a hormone binds to its receptor on the cell membrane. This activates a G-protein, which in turn, activates the membrane-bound enzyme adenylyl cyclase. Adenylyl cyclase converts ATP to cAMP, leading to the activation of protein kinases and subsequent gene transcription.