Final answer:
Short-lived Ras signals are propagated through the cell using the MAPK cascade pathway, where the Ras protein activates RAF, which activates MEK, and finally MEK phosphorylates ERK to trigger a cell response.
Step-by-step explanation:
Short-lived Ras signals are propagated through the cell using a signaling pathway called the MAPK cascade. When a ligand binds to a receptor on the cell surface, it initiates a series of events where the Ras protein, an important G-protein, is activated. The activated Ras protein then activates a kinase called RAF, which in turn phosphorylates another kinase called MEK. Finally, MEK phosphorylates the MAP kinase (ERK), which enters the nucleus and triggers a cell response by phosphorylating transcription factors and other nuclear proteins.