Final answer:
Cyclic AMP activates cAMP-dependent kinase (PKA), which phosphorylates substrate proteins leading to various cellular responses. Activation of PKA is pivotal for metabolic regulation, gene expression, and other cell processes. The cAMP signal is terminated when it is converted into AMP by phosphodiesterase.
Step-by-step explanation:
Cyclic AMP activates cAMP-dependent kinase, also known as protein kinase A or PKA. This enzyme plays a crucial role in cellular processes by acting as a second messenger that can activate or inactivate various protein targets within the cell. The process begins with the activation of a G-protein, which then activates adenylyl cyclase. This enzyme catalyzes the conversion of ATP to cAMP. Upon formation, cAMP binds to and activates PKA by binding to its regulatory subunits, which leads to a conformational change that releases the active catalytic subunits of PKA.
These active PKA enzymes catalyze the phosphorylation of serine and threonine residues on substrate proteins, thereby altering these proteins' functions. Such changes can initiate cascades of further activations that lead to numerous cellular responses, including gene expression, metabolic regulation, and other vital cellular processes. Eventually, the signal is terminated when an enzyme called phosphodiesterase converts cAMP into AMP, thus stopping the activation of PKA.