Final answer:
True, the amplification of a signal can occur when Protein Kinase A phosphorylates target proteins, as this is a crucial step in cellular signal transduction and response.
Step-by-step explanation:
An amplification of a signal could indeed occur when Protein Kinase A (PKA) phosphorylates target proteins. This process is fundamental to signal transduction, which is the mechanism by which cells respond to external signals like hormones. The binding of a hormone to a receptor activates a kinase activity that, through a series of enzyme phosphorylations known as the phosphorylation cascade, leads to cellular responses.
The phosphorylation usually results in a change in protein shape, thereby activating or inactivating these target proteins. PKA especially is involved in phosphorylating proteins on serine and threonine residues, an action that can enable these proteins to alter cell activity. Consequently, the phosphorylation by PKA is a pivotal step in the amplification and propagation of cellular signals.