What is meant by signal amplification? Provide two examples.

Signal amplification occurs when a signaling molecule bound to a receptor produces changes in millions of molecules in a cascade of reactions. This explains how a few signal molecules, that is, neurotransmitters, ions, or hormones molecules can lead to major responses in a cell. Epinephrine binding to a G-protein receptor activates adenylyl cyclase which catalyzes the production of many cAMP molecules. Each cAMP activates many protein kinases down a cascade of reactions. The Ras/MAP kinase is stimulated by epidermal growth factor binding to a tyrosine kinase receptor. This binding leads to the activation of the G small protein. Ras then activates the MAP-kinase signaling pathway. A series of MAP kinases in the pathway are then activated by phosphorylation.