Extracellular Enzymes

Cellular reactions require substrates.All substrates are obtained from the environment.Many of the materials obtained from the environment are large molecules which must be broken down into smaller, simpler molecules before they can be used by the cells for anabolic or catabolic reactions.The molecules obtained from these nutrients may be used to form polymers such as proteins and polysaccharides or may be broken down to provide energy for the cell in the form of ATP.Extracellular enzymes are released from the cells to break down the nutrients into smaller molecules in a process called digestion.The smaller molecules are then absorbed into cells.Unicellular organisms release enzymes into the outside environment. The extracellular enzymes break down starch and proteins. The amino-acids and glucose are then absorbed into the cell.Multicellular organisms eat food and break down the macromolecules in the digestive system. The amino-acids, glucose and other small molecules are then absorbed into the blood.