What are the steps in the signal transduction pathway?

The signal transduction pathway is divided into 3 steps: signal reception, signal transduction, and cellular response, in that order respectively. During signal reception, a cell detects a signaling molecule from the exterior of the cell. A signal becomes detected when a ligand binds to a receptor protein on the surface or the interior of the cell. These receptors are known as membrane receptors, and once they are bound to the signal molecule (ligand). During transduction, the signaling molecule changes the cell-surface receptor protein. The signal is relayed by each molecule altering the next molecule in the pathway. Second messengers, activated proteins, and enzymes interact with specific proteins, which become activated in a chain reaction to convert extracellular signals to intracellular signals. This generates a specific cellular response, which is the last step of the signal transduction pathway. Many signaling pathways regulate the synthesis of proteins by turning genes on or off. In some pathways the final molecule can function as a transcription factor which initiates transcription and activates genes. In other pathways, the final molecule may have the opposite effect and instead inactivate genes and inhibit transcription.