The school definition says that enzymes are biological catalysts. Enzymes are protein molecules. Enzymes increase the rate of reaction in a cell without the enzyme being used up. Enzymes increase the rate of only one type of biological reaction. Enzymes act on specific molecules. Researchers estimate that a single cell may contain up to 3,000 enzymes.
The simplest explanation of how an enzyme works is the lock-and-key model. The enzyme protein binds to a molecule whose shape exactly matches so the two pieces lock in place like two puzzle pieces.
In one second, a single enzyme molecule in your blood can catalyze the decomposition of 600,000 carbohydrate molecules. In that second your lungs exhale 600,000 molecules of carbon dioxide from that bite of pizza.
There are three classes of enzymes: metabolic enzymes, digestive enzymes, and food enzymes. Metabolic enzymes run the human body. Digestive enzymes digest food. Food enzymes come from raw foods and start food digestion. Enzymes do not survive in heat. Cooked food lacks the food enzymes found in raw foods.
Amylase is an enzyme found in saliva that breaks down starch into glucose or sugar units. The body can metabolize glucose but not starch. In one second, amylase in saliva can free 18,000 glucose molecules from a potato. Pepsin is the enzyme that decomposes albumin in egg whites and other proteins; Pepsin is found in the stomach. Lipase digests fat; Lipases are secreted by the pancreas and the intestines. Lactase digests lactose; lactose is found in milk and is produced in muscles as you exercise.
Alcohol dehydrogenase helps metabolize ethanol (wine, beer, whiskey). Proteases are protein digesting enzymes. Chymotrypsin and tripsin are secreted by the pancreas. Proteases break the chemical bonds in proteins down into amino acids. Peptidases also contribute to the final stages of protein digestion.
All these chemical reactions take place at body temperature because of the enzymes. Most chemical reactions require heat to complete them. Certain biological reactions require enzymes to complete them.
Individuals who are lactose intolerant are not able to digest the lactose or sugar in milk. They do not produce lactase, the enzyme that aids in the digestion of milk.
Some detergents advertise an enzyme additive to help get stains out of clothes. Since many stains are protein, blood, or fat based, it is logical that enzymes would help to break up these complex molecules and aid in the emulsification process that allows detergents to lift stains from fabric. There is some argument whether these laundry enzymes are natural or manufactured products.