noun, plural: mitochondria
The mitochondrion is regarded as the powerhouse of eukaryotic cells. That is because it is the organelle that supplies energy by generating adenosine triphosphate (ATP) through cellular respiration.
The mitochondrion consists of outer and inner membranes, an intermembrane space (space in between the membranes), the cristae (infoldings of the inner membrane), and the matrix (space within the inner membrane). The outer membrane contains several porins that form channels where certain molecules can freely diffuse. Unlike the outer membrane, the inner membrane does not contain porins and is highly impermeable to all molecules. Most ions and molecules would need special membrane transporters to enter or exit the matrix. The cristae, which are the foldings of the inner membrane, increase the surface area thereby increasing ATP production. The matrix contains enzymes, mitoribosomes, tRNA, and DNA. The mitochondrial DNA is genetically distinct from that in the nucleus. Since a mitochondrion has its own genetic material, and is capable of manufacturing its own RNAs and proteins, it is said to be a semi-autonomous, self-reproducing structure. In fact, the mitochondrial DNA has become an important tool in tracking genetic histories since the genetic material is present in only one copy, and does not recombine during reproduction.
It produces large amounts of energy through oxidative phosphorylation of organic molecules during cellular respiration. It is capable of using glucose and oxygen to produce energy (and releasing carbon dioxide and water in the process) for use in many metabolic processes. Thus, it is not surprising to find several mitochondria in high energy-requiring cells, such as muscle cells. There are cells that lack mitochondrion, such as mature red blood cells of mammals.
It is thought that the mitochondria might have originated from early bacteria that became so symbiotic with their hosts, the eukaryotic cells, that they evolved and become indispensable energy-yielding structures within the eukaryotic cells (endosymbiotic theory). Nevertheless, there is a eukaryote that lacks mitochondrion. Monocercomonoides is the first eukaryotic species found to be devoid of mitochondria, and obtains energy by metabolizing nutrients absorbed from the environment.
Word origin: Greek mitos, thread + khondrion, little granule.
- mitochondrial (adjective, of, or relating to, mitochondrion)