Enzymes can be grouped by where they act.Intracellular enzymes are made and act inside cells. They may be free in the cytoplasm or inside organelles. Examples:
• catalase, found in most cells, breaks down hydrogen peroxide, a toxic by-product of metabolism, into water and oxygen: 2H2O2 → 2H2O + O2
• DNA polymerase and RNA polymerase in the nucleus
• the enzymes of respiration in the cytoplasm and mitochondriaExtracellular enzymes are made inside cells but secreted to act outside them. The protein is made on ribosomes of the rough endoplasmic reticulum, modified and packaged in the Golgi apparatus, and released in vesicles by exocytosis. Examples:
• amylase, from the salivary glands and pancreas, hydrolyses starch to maltose
• trypsin, made in the pancreas and acting in the small intestine, hydrolyses proteins to peptides
• fungi and bacteria secrete extracellular enzymes onto their food and absorb the soluble products (saprotrophic nutrition)Extracellular enzymes let organisms break large molecules, which cannot cross cell membranes, into small soluble molecules that can be absorbed.
Worked example: lipase is made by cells in the pancreas and acts on fats in the small intestine. It acts outside the cells that made it, so it is an extracellular enzyme.
• catalase, found in most cells, breaks down hydrogen peroxide, a toxic by-product of metabolism, into water and oxygen: 2H2O2 → 2H2O + O2
• DNA polymerase and RNA polymerase in the nucleus
• the enzymes of respiration in the cytoplasm and mitochondriaExtracellular enzymes are made inside cells but secreted to act outside them. The protein is made on ribosomes of the rough endoplasmic reticulum, modified and packaged in the Golgi apparatus, and released in vesicles by exocytosis. Examples:
• amylase, from the salivary glands and pancreas, hydrolyses starch to maltose
• trypsin, made in the pancreas and acting in the small intestine, hydrolyses proteins to peptides
• fungi and bacteria secrete extracellular enzymes onto their food and absorb the soluble products (saprotrophic nutrition)Extracellular enzymes let organisms break large molecules, which cannot cross cell membranes, into small soluble molecules that can be absorbed.
Worked example: lipase is made by cells in the pancreas and acts on fats in the small intestine. It acts outside the cells that made it, so it is an extracellular enzyme.