Final answer:
Second messengers propagate a signal after binding of a signaling molecule to a receptor, spreading the signal through the cytoplasm by altering cellular protein behavior. Ligand binding to a plasma membrane hormone receptor initiates a signal transduction pathway, involving the activation of second messengers like cAMP, Ca²+, DAG, and IP3 to transmit the signal within the cell.
Step-by-step explanation:
Second messengers are small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor. These molecules help to spread a signal through the cytoplasm by altering the behavior of certain cellular proteins. When a ligand binds to a plasma membrane hormone receptor, it triggers a signal transduction pathway. This pathway involves the activation of second messengers, such as cyclic AMP (cAMP), calcium ions (Ca²+), diacylglycerol (DAG), and inositol triphosphate (IP3), which transmit the signal within the cell.