Final answer:
The statement that PKA, a tetramer, binds to 2 molecules of cAMP before activation is false; it actually binds 4 cAMP molecules for full activation.
Step-by-step explanation:
Protein kinase A (PKA) is indeed a tetramer that requires binding to cyclic AMP (cAMP) for activation, but the statement that it binds to 2 molecules of cAMP before activation is false. In fact, each regulatory subunit of PKA binds to one molecule of cAMP, totaling four cAMP molecules for full activation of PKA. The process begins with the conversion of ATP to cAMP by adenylyl cyclase. This cAMP then binds to the regulatory subunits of PKA, causing a conformational change that leads to the dissociation of the tetramer, releasing two active catalytic subunits that can then catalyze the phosphorylation of other proteins, such as phosphorylase kinase, leading to subsequent cellular responses.