The mitochondria is called the powerhouse of the cell because it is responsible for producing most of the cell's energy, or adenosine tri-phosphate (ATP). Mitochondria are able to multiply in response to the energy needs of a cell, so that cells requiring more energy to function are powered by more mitochondria than cells with lower energy needs.
Mitochondria are thought to have been created early in the evolution of organisms when a cell containing a nucleus absorbed an aerobic prokaryote. The two cells entered into a mutually productive relationship, in which the surrounding cell provided protection to the prokaryote, and the prokaryote provided energy for the surrounding cell. The descendants of these cells evolved into mitochondria. This explains the many similarities seen today between mitochondria and prokaryotes, such as the presence of electron transport proteins in the membranes of both. While prokaryotes are able to synthesize their own proteins, mitochondria have lost this ability over time, and rely heavily on the nucleus of the host cell for this function.
After food is eaten, digestive products make their way to the individual cell. The digestive products then undergo a series of chemical reactions that changes them into ATP, the form of energy that cells are able to absorb. Leftover fragments from the chemical processes then enter the mitochondria and are changed chemically into carbon dioxide and water. These substances are then transformed by the mitochondria into additional ATP for the cell to use as energy.
The initial process that changes digestive products to ATP within the cell is called glycosis, and produces two ATP per glycogen molecule. After the waste product of glycosis, called pyruvate, enters the mitochondria, the resulting process generally produces between 34 and 36 ATP.
Free Radical Production
A byproduct of mitochondria's ATP production, free radicals have the ability to severely damage or kill cells. They can destroy DNA, RNA, and other crucial components of a cell. Luckily, mitochondria have their own internal defense system against free radicals, called antioxidant enzymes, that block any damage the free radicals could do to the cell. Scientists believe that some free radicals are actually used by mitochondria as a measuring stick to sense whether the level of ATP production in a cell needs to be adjusted.
Mitochondria play a key role in determining the overall health of an individual. Lack of exercise decreases the efficiency and amount of mitochondria in muscle cells, making it more likely for free radicals to do cell damage. Excess consumption of sugar-heavy foods and beverages also decreases the efficiency of mitochondria. Regular exercise and a diet rich in fruits, vegetables, and antioxidants benefits mitochondrial health in individuals of all ages.