In biology, cell signaling (cell signalling in British English) is part of any communication process that governs basic activities of cells and coordinates multiple-cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity, as well as normal tissue homeostasis. Errors in signaling interactions and cellular information processing may cause diseases such as cancer, autoimmunity, and diabetes. By understanding cell signaling, clinicians may treat diseases more effectively and, theoretically, researchers may develop artificial tissues.[4]Systems biology studies the underlying structure of cell-signaling networks and how changes in these networks may affect the transmission and flow of information (signal transduction). Such networks are complex systems in their organization and may exhibit a number of emergent properties, including bistability and ultrasensitivity. Analysis of cell-signaling networks requires a combination of experimental and theoretical approaches, including the development and analysis of simulations and modeling.[5][6] Long-range allostery is often a significant component of cell-signaling events.[7] All cells receive and respond to signals from their surroundings. This is accomplished by a variety of signal molecules that are secreted or expressed on the surface of one cell and bind to a receptor expressed by the other cells, thereby integrating and coordinating the function of the many individual cells that make up organisms. Each cell is programmed to respond to specific extracellular signal molecules. Extracellular signaling usually entails the following steps:Synthesis and release of the signaling molecule by the signaling cell; Transport of the signal to the target cell;Binding of the signal by a specific receptor leading to its activation;Initiation of signal-transduction pathways.