Everyone knows that the body uses sugar for energy. Advertising claims that high glucose drinks and bars produce quick energy are made every day. However, fewer people know that sugar is used to create high-energy phosphate groups. These phosphate groups provide the energy for enzymes to perform all the biochemical activities needed to sustain life.
Cellular Respiration
The process of breaking glucose down to pyruvate is called cellular respiration. This process involves three complex sets of biochemical pathways: glycolysis, the Krebs cycle and oxidative phosphorylation. The important product from these three pathways is not the pyruvate, but the adenosine triphosphate molecules, better known as ATP, that are formed during this process. In an ideal system, 38 ATP molecules are formed during the breakdown of a single glucose molecule.
ATP
An ATP molecule is made from the nucleic acid adenosine and three phosphate groups. The chemical bond between the phosphate groups and the adenosine is a high-energy bond. This means that energy is released when the bond is broken. Many enzymes require ATP to catalyze reactions. These reactions cannot occur without the energy release that occurs when the phosphate bond is broken. ATP becomes adenosine diphosphate, or ADP, when the first phosphate bond is broken. ADP becomes adenosine monophosphate, or AMP, when the second phosphate bond is broken.
Mitochondria
The first part of cellular respiration, or glycolysis, happens in the cytoplasm. Cytoplasm is a gel-like substance outside the nucleus of the cell. The second and third parts of cellular respiration -- the Krebs cycle and oxidative phosphorylation -- take place in the mitochondria.
Middle school teachers tell students that the mitochondria are the "powerhouse" of the cell. The mitochondria have this nickname because so many ATP molecules with high-energy phosphate groups are made there.
Glycogen
If your body takes in too much glucose to use immediately, it is stored as the starch glycogen. The glycogen molecule is converted back to glucose during the course of the day to keep your blood sugar levels up between meals. This glucose is systematically broken down to produce ATP with high-energy phosphate groups.
