Genes encode proteins, and proteins often work like minuscule molecular switches, activating yet other proteins and inactivating others, turning molecular switches “on” and “off” inside a cell. Thus, a conceptual diagram can be drawn for any such protein: protein A turns B on, which turns C on and D off, which turns E on, and so forth. This molecular cascade is termed the signaling pathway for a protein. Such pathways are constantly active in cells, bringing signals in and signals out, thereby allowing a cell to function in its environment.
