ATP is short for adenosine triphosphate, a crucial chemical in human metabolism that has been called "chemical currency" because the cells use it as a direct source of energy. You make ATP when you burn sugars and other nutrients, and your cells consume ATP when they engage in activities like building larger molecules and producing movement.
ATP is a relatively small molecule that serves as an "energy intermediate" in human metabolism. In essence, your cells extract the chemical energy from various nutrient molecules like proteins, carbohydrates and proteins, and use the chemical energy to make ATP. The cells then break down ATP, releasing energy, as they engage in a variety of activities, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
When you consume foods, your intestine absorbs the nutrient molecules into the bloodstream. Cells then take up these nutrients and chemically burn them to liberate energy. For instance, one of the most important sources of cellular energy is glucose, a molecule that comes from starch and many dietary sugars. As the cells break down glucose, they produce the waste products carbon dioxide and water. They use the energy liberated from breaking down a single molecule of glucose to make approximately 30 molecules of ATP.
Once a cell has made ATP, it can use the ATP to fulfill any of its energy needs. Cells need energy to make large molecules, like hormones. Muscle cells use ATP to produce movement. As a cell makes a hormone molecule, it breaks down molecules of ATP and uses the energy to make new bonds between smaller molecules in order to produce a larger one, explain Drs. Garrett and Grisham. When a muscle cell contracts, it uses large quantities of ATP to fuel the contraction.
Even though human cells can make about 30 ATP per glucose molecule -- and can also make large and varying amounts of ATP from burning protein and fat -- not all glucose metabolism results in the production of that much ATP. You can only make two ATP molecules per glucose if you're burning sugar without oxygen, a process called anaerobic metabolism. Dr. Lauralee Sherwood, in her book "Human Physiology," explains that cells operate anaerobically during hard sprint or power efforts, such as during a very hard workout.
One final important role of ATP in the body is to serve as a cellular signal. For instance, since your cells can either burn nutrients immediately or store them for later use, the cells use ATP to help them determine which they should do. If a cell has plenty of ATP, the ATP signals the cell to store nutrients rather than burning them. If a cell is low on ATP, however, that signal indicates that the cell should burn nutrients immediately.