John Hickman, age 14, of Jackson, Miss., for his question:

JUST WHAT IS AN ENZYME?

An enzyme is a protein molecule that helps chemical reactions to take place in all animals and plants. In other words, an enzyme is a catalyst.

All living cells make enzymes but enzymes are sot alive. Enzyme molecules function by altering other plant or animal molecules. Enzymes combine with the changed molecules to make a complex molecular structure in which chemical reactions take place.

The enzyme, which doesn't change, then separates from the product of the reaction. A single enzyme molecule can perform its entire function a million times a minute. The chemical reactions take place thousands or even millions of times as fast is the presence of enzymes as they would without enzymes.

There are more than a thousand types of enzymes is the human body. Each type of enzyme handles one specific job. If you didn't have enzymes in your body, you wouldn't be able to breathe, see, digest food or move any part of your body.

Some of your enzymes break down complex substances into simpler ones while others build complex compounds from simple ones. Although most enzymes stay in the cells where they were formed, some do their work elsewhere. An example of this is found in the enzyme called amylase which the pancreas secretes but which travels to the small intestine to break down carbohydrates.

Two Greek words meaning "in yeast" were used to form the word "enzyme." The reason for this is that many of the scientists who studied enzymes during the 1800s watched reactions caused by yeast enzymes.

It was in 1926 that an American biochemist named James Summer became the first person to isolate a pure enzyme in the form of crystals. He extracted the enzyme called urease from beans.

In 1969 the first man made enzyme was created by scientists. It was called ribonuclease and it was made from amino acids.

Even the most powerful light microscope isn't strong enough to allow us to see the tiny enzyme. Scientists know by way of various research projects, however, that they come in a number of shapes and sizes.

Enzymes break down food throughout the entire digestive system. It starts is the mouth where the salivary glands produce as enzyme called salivary amylase, which splits carbohydrates into simpler chemicals.

Pepsin, which is secreted by the wails of the stomach, acts on proteins and you already know how enzymes from the pancreas go to work is the small intestines.

Enzymes have many uses in addition to their natural functions in the body. Manufacturers use enzymes in making a number of products including some detergents. Enzymes break down protein matter, such as perspiration, that can cause stains.

Enzymes are also used in antibiotic:, beer, bread, cheese, coffee, meat tenderizers, vinegar, vitamins and many other products.