What is Active Site

To qualify as living, units of life called cells must be identifiable, distinct, and demonstrate most or all the qualities of life. Cells tremendously vary in size from about 0.5-500 micrometers. The smallest known single cells are those of bacteria while most higher organisms have multiple cells differentiated and functioning together as a single system. Communication in cells involves cell signaling, reception, transduction, and response. Signals received at the surface of the cell from other cells, or from blood or tissue fluid must be transferred to various parts of the cell and a cell response initiated. Cells actively take in raw materials which they use to function and perform maintenance activities. Collectively these activities are called cellular metabolism catalysed by enzymes. To avoid chaos in the body, cells maintain control of what reactions are needed all the time, needed only certain times or needed very rarely. This chapter explores the cellular basis of life.