Fran Binder, age 13, of Bowling Green, Ohio, for her question:

HOW MANY DIFFERENT ENZYMES ARE IN THE BODY?

An enzyme is a protein molecule that speeds up chemical reactions in all plants and animals. Without enzymes, these reactions would occur too slowly or not at all, and no life would be possible. The human body contains more than 1,000 different types of enzymes.

Each kind of enzyme in the human body performs one specific job. Without enzymes, a person could not breathe, see, digest food or even move any part of his body.

All living cells make enzymes, but enzymes are not alive. Enzyme molecules function by altering other plant or animal molecules. Enzymes combine with the altered molecules to form a complex molecular structure in which chemical reactions take place. The enzyme, which remains unchanged, then separates from the product of the reaction. Enzymes thus serve as catalysts.

A single enzyme molecule can perform its entire function a million times a minute. The chemical reactions occur thousands or even millions of times as fast in the presence of enzymes as they would without enzymes.

Many enzymes break down complex substances into simpler ones. Others build complex compounds from simple ones. Most enzymes remain in the cells where they were formed, but some do their work elsewhere.

The word "enzyme" comes from two Greek words meaning "in yeast." Many of the scientists who studied enzyme reactions in the 1800s studied reactions caused by yeast enzymes.

Enzymes break down food throughout the entire digestive system in the human body. The salivary glands produce an enzyme called salivary amylase, which splits carbohydrates into simpler chemicals. Pepsin, secreted by the walls of the stomach, acts on proteins. Pancreatic lipase is secreted by the pancreas into the small intestine, where it breaks down fats. Other enzymes perform various other functions.

An American biochemist named James Sumner was the first person to isolate a pure enzyme.

Sumner in 1926 came up with a pure enzyme in the form of crystals. He extracted the enzyme called unease from beans.

In 1969, scientists created the first man made enzyme, ribonuclease, from amino acids. This enzyme breaks down ribonucleic acid into molecules of other amino acids.

Enzymes are too small to be seen even with the moat powerful microscopes. However, scientists know through various research techniques that enzymes occur in a number of shapes and sizes.

Although enzymes of different plants and animals have different protein structures, they function in similar ways. The structure of any particular enzyme enables it to cause certain chemical reactions in other molecules.

Enzymes have many uses in addition to their natural functions in the body. Manufacturers, for example, use enzymes in making a wide variety of products. Enzymes are used in some detergents, antibiotics, bread, cheese, meat tenderizers, vinegar, vitamins and many other products.