Final answer:
The four essential components in a signaling pathway include the receptor, ligand, second messengers, and effector proteins or enzymes. After the ligand binds to the receptor, a signaling pathway is activated, involving protein phosphorylation and signal transmission by second messengers.
Step-by-step explanation:
In cell signaling, the four essential components in a signaling pathway are typically the receptor, the ligand (also known as a signaling molecule), second messengers, and effector proteins or enzymes. More specifically, after a ligand binds to a cell-surface receptor, it triggers a sequence of events referred to as a signaling pathway or signaling cascade. This pathway involves the activation of the receptor's intracellular components leading to the activation or inactivation of other proteins in the cell. A major component of cell signaling is the phosphorylation of proteins by enzymes such as kinases. This phosphorylation can change a protein's shape and, consequently, its activity. Second messengers, which are small, non-protein molecules, such as calcium ions (Ca²⁻), cyclic AMP (cAMP), and others, play a critical role in transmitting signals within the cell.
Therefore, the correct answer to the student's question is option 1) Receptor, ligand, effector, and signaling molecule.