What are Mitochondria?
Mitochondria are structures that are found inside virtually every cell. Of all the 250 cell types in the body, only the mature red blood cell does not contain mitochondria. Each cell may have thousands of mitochondria, or as few as two, depending on the cell type and its energy need. The name “mitochondrion” means “thread-like” and comes from the way these structures may look under the microscope. Mitochondria can have different shapes, however, which are characteristic of the cell type where they reside. Each mitochondrion has an outer membrane and an inner membrane. Embedded within each membrane are unique proteins that carry out specific functions required for cellular energy and metabolism. Many functions of the mitochondria are linked to the specialized cell type in which it is found. Mitochondria possess their own DNA, unique from the cell’s nuclear DNA. Mitochondrial DNA is small and circular, not linear like nuclear DNA. It more closely resembles the DNA of bacteria.
Mitochondria are tiny cellular bodies or organelles, and are among the most complex structures within the cell. They have both an outer and inner membrane. Most of the energy-producing reactions occur at the inner membrane, which is made of lipids (fats) studded with proteins. Anything that compromises this structure can undermine the ability of the mitochondria to produce energy. Mitochondria also contain a small loop of DNA. Mitochondrial DNA Mitochondria are the only components of cells, apart from the nucleus, to possess DNA. Mitochondrial DNA is much shorter than nuclear DNA, but no less important. Most mitochondrial proteins have their origin in the cell’s nuclear DNA; these proteins are imported into the mitochondria. But a number of proteins essential to energy production come from mitochondrial DNA, and damage to this DNA can cripple the ability of the mitochondrion to produce energy. Bacteria in disguise?
Mitochondria are sometimes referred to as the “power plants” of the cell because they manufacture energy for the cell. Mitochondria contain DNA (mtDNA); this DNA is not inherited in the same pattern as nuclear DNA (DNA in our chromosomes). While each parent contributes half of their nuclear DNA to the child’s DNA, only mothers pass their mitochondrial DNA to each of their sons or daughters. Fathers cannot pass their mtDNA on to their children. This special inheritance pattern allows us to use mtDNA to track maternal lineage.
Mitochondria (my-toe-con’-dree-a) are small “organs” in our cells. They are the cell’s power plant. They use oxygen, fat and sugar to produce adenosine triphosphat (ATP). This process is called “cellular respiration.” When the cell needs energy, it breaks down molecules of ATP to release the stored energy. The more energy the cell needs, the more mitochondria it contains. One cell can have anywhere from a few mitochondria up to thousands. The highest numbers are found in nerve, muscle, and liver cells. Some scientists believe that mitochondria are the key to aging. As we grow older, our mitochondria collect more and more mutations. Our cells have a way to check for mistakes (mutations) when they multiply, but mitochondria don’t. Eventually, mutations or a lower number of mitochondria can reduce the energy available to the cell. If the energy drops low enough, the cell can malfunction. If the energy drops even further, the cell will stop working.
