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Colleen Rozene, age 13, of Brimfield, Ill., for her question:

WHAT IS ATP?

Each cell in the body is very active. It must carry out most of life's functions, including growth and reproduction. In addition, cells of multicellular organisms have special jobs. To live and to do its work, a cell must produce energy. It must also manufacture proteins for the construction of its parts and to speed up the many chemical reactions that take place in the cell.

Most of a person's energy comes from the mitochondria, the power producers of a cell. The mitochondria are like a power plant which burns fuel to produce the electricity that runs machines.

The food a person eats is the fuel that is actually burned inside the mitochondria. A product of this burning is a compound called adenosine triphosphate. These two difficult words are called, simply, ATP.

ATP is actually the electricity that runs the cell's activities. It supplies the energy when a protein is made, a muscle cell contracts, a nerve cell sends a message or a gland cell produces a chemical.

An ATP molecule is made up of three substances: adenine, ribose and three phosphate groups. The--three phosphate groups are linked one to another like railroad cars because of a chemical bond, or a force that holds some atoms together. The bond that holds the last two phosphate groups together is especially rich. When it is broken, energy is released.

ATP is produced in animal cells through a very complicated process. The digestive system breaks protein down into amino acids, fats into fatty acids and sugar and starches into simple sugars. The sugars are broken down into pyruvic acid and a small amount of ATP is produced.

Amino, fatty and pyruvic acids then enter the mitochondria. Enzymes in the mitochondria break down these substances further in a series of chemical reactions. With the addition of oxygen, carbon dioxide and water, many molecules of ATP are produced. The ATP molecules then leave the mitochondria and provide power wherever it is needed in the cell. For every job that is done, enzymes break the ATP phosphate bonds and release the energy.

During photosynthesis--the process by which green plants make sugars--ATP is also produced. When the chlorophyll molecule is struck by sunlight in a chloroplast, it sets off a series of chemical reactions. A result of these reactions is the formation of ATP. ATP supplies the energy which plants then use to turn carbon dioxide from the air to oxygen and water from the soil into sugars.

 

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