Enzymes are large molecules made of protein that catalyze, or increase the speed, of chemical reactions in organisms. Without enzymes it would be impossible for these chemical reactions to occur at the speed of life. Enzymes lower the activation energy, or the minimum amount of energy needed to start a chemical reaction. They are very selective and are never used up; enzymes can be used over and over again. In animals and humans, enzymes are essential for breaking down our food - proteins, fats and carbohydrates are broken down so they can be absorbed through our intestinal walls.http://www.youtube.com/watch?v=feik6wOXFA0&feature=player_embedded  

Each type of enzyme is specialized for a specific reaction and has a unique 3-dimensional structure which allows it to fit with the substrate, at its active site, to facilitate a reaction. Enzymes are needed for all of the biochemical reactions that occur in organisms, including those related to digestion and functioning of the circulatory, immunological, nervous and muscular systems in vertebrates. There are various inherited disorders in humans that result in enzyme deficiencies, such as mucopolysaccharidosis and Nieman-Pick disease. Enzymes are also necessary in food microbiology for the production of cheese, yogurt, alcohol, soy sauce and vinegar.http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/01q.html http://www.nfctr.org/rar_childhood_disorders.php#enzyme http://web.fccj.edu/~dbyres/enzyme1.html