Biosynthesis is the process by which living cells manufacture complicated chemical compounds from simpler substances. For example, simple molecules called amino acids are put together to make proteins. In plants, carbon dioxide is synthesized into sugars and starch.
Like a factory, every cell needs raw materials, workers, and a power source before it can turn out its products. The raw materials for biosynthesis are the relatively simple chemical compounds that human beings and animals obtain from digested food; that plants obtain from photosynthesis and respiration; and that microorganisms, such as bacteria and yeast, take from their surroundings. The workers of the cell are enzymes, molecules that speed up biochemical reactions. Most enzymes are proteins. A cell contains from hundreds to thousands of kinds of enzymes. Each kind is responsible for speeding up a specific reaction or group of similar reactions.
One of the cell’s major power sources is adenosine triphosphate (ATP), which is a compound that is rich in energy. Special enzymes release the energy contained in ATP whenever power is needed to drive a reaction. Human beings and animals, and most bacteria, constantly restock their supplies of ATP by taking energy released from digested food. Plants renew their ATP supplies chiefly by trapping energy from the sun.
See also Cell (The work of a cell).
