Mitochondrion
Introduction
The mitochondrion is a double-membraned organelle found in most eukaryotic organisms. Often referred to as the "powerhouse of the cell", mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in other tasks, such as signaling, cellular differentiation, and cell death, as well as maintaining control of the cell cycle and cell growth.
Structure
Mitochondria are typically between 0.75 and 3 micrometers in diameter but vary considerably in size and structure. Unless specifically stained, they are not visible. Mitochondria, being the site of nearly all energy production in eukaryotic cells, are remarkably flexible and can change shape rapidly. They can appear as long, interconnected networks or as discrete, individual organelles, depending on the cellular environment and the cell's energy needs.
Function
Mitochondria are the site of most of the cell's production of ATP, which provides cells with a readily usable form of chemical energy. They also have their own DNA, separate from the nuclear DNA of the cell, and can replicate independently of the cell in which they reside. This has led to the theory that mitochondria are the descendants of a prokaryotic organism that was engulfed by an early eukaryotic cell.
Mitochondrial DNA
Mitochondrial DNA (mtDNA) is a small circular genome located within mitochondria. In most species, including humans, mtDNA is inherited solely from the mother. Mutations in mtDNA can lead to a number of diseases, including mitochondrial diseases and some forms of cancer.
Mitochondrial diseases
Mitochondrial diseases are a group of disorders caused by dysfunctional mitochondria. They are the result of either inherited or spontaneous mutations in mtDNA or nDNA which lead to altered functions of the proteins or RNA molecules that normally reside in mitochondria. Because of the central role of mitochondria in energy production, many mitochondrial diseases affect high-energy organs like the brain, heart, and muscles.
Biogenesis and dynamics
Mitochondria are dynamic organelles that can change shape, size, number, and location in response to cellular needs. This is achieved through the processes of mitochondrial fusion and fission. Mitochondrial biogenesis, the process by which new mitochondria are formed in the cell, is largely regulated by the nuclear genome.
Role in apoptosis
Mitochondria play a central role in apoptosis, or programmed cell death. They release proteins that initiate apoptosis, effectively triggering the cell's own death. This process is vital for the development and maintenance of healthy tissues and organs.
Evolutionary origin
The endosymbiotic theory proposes that mitochondria originated from a symbiotic relationship between an early eukaryotic cell and a prokaryotic cell. The prokaryotic cell was engulfed by the eukaryotic cell, but instead of being digested, it was retained and became an integral part of the host cell.