Final answer:
Changes in protein phosphorylation occur more rapidly than changes in protein synthesis in response to extracellular signals. Protein phosphorylation can quickly modify protein function and gene expression, whereas protein synthesis is a longer, more complex process.
Step-by-step explanation:
In response to an extracellular signal, the changes in protein phosphorylation are likely to occur more rapidly than changes in proteins being synthesized. Protein phosphorylation involves the addition of a phosphate group to a protein, changing its shape and thereby activating or inactivating it, often involving enzymes known as kinases. In contrast, the synthesis of new proteins is a longer process which includes transcription and translation. For example, during a signal transduction pathway like the MAP-kinase cascade or the binding of epinephrine (adrenaline) to a G-protein-linked receptor, phosphorylation cascades are initiated, which can quickly alter the activity of existing proteins and lead to various cellular responses, including alterations in cellular metabolism and cell division. Phosphorylation can influence gene expression by modifying the function of transcription factors, which then enter the nucleus and interact with DNA to alter transcription.