This article describes an organelle, a cell component with its own distinctive structure and function. In eukaryotic cells, this is bounded by its own membrane, which is a lipid bilayer made of phospholipid.
Mitochondrion (plural mitochondria) is an organelle found in eukaryotic cells whose primary function is to carry out aerobic respiration, i.e., convert energy from a relatively more hard-to-use form (pyruvates) to energy stored in the form of ATP.
|Type of organisms whose cells contain mitochondria||eukaryotic cells only, both plant cells and animal cells|
|Type of cells within the organisms that contain mitochondria||All cells except red blood cells in mammals (other vertebrates do have mitochondria in their red blood cells).|
|Number of mitochondria per cell||1 to 1000s, depending on the energy needs of the cell|
|Size||diameter per mitochondrion. In some cells, they could together take up to 1/5 of the cell volume|
|Location within cell||Could be found anywhere in the cell, depending on the cell's energy needs. For instance, in sperm cells, mitochondria are found in the tail to provide power for propulsion.|
|Structural components||outer mitochondrial membrane, intermembrane space, inner mitochondrial membrane, cristae, mitochondrial matrix|
|Chemical constituents||lots of proteins|
|Control of the entry and exit of materials||Membranes (hydrophilic/hydrophobic issues), the TIM/TOM complex|
|Function||aerobic respiration, i.e., ATP synthesis|
Control of cell cycle
|Evolutionary origin||endosymbiotic theory of mitochondrial origin -- the mitochondria are evolutionary descendants of endosymbionts (organisms living in the cell in a mutually beneficial relationship with their host)|
|Variation between individuals||Mitochondria have their own DNA which (in most eukaryotic organisms) is inherited from the mother. In addition, some of the behavior of the mitochondria is controlled by nuclear DNA.|
Diameter and volume
The diameter of mitochondria is in the range (microns), where one micron is .
Comparison with cell sizes
Comparison with prokaryotic cells: The mitochondrion size is roughly the lower end of the size range for prokaryotic cells (which is explained by their evolutionary origin; see endisymbiotic theory of mitochondrial origin).
Comparison with eukaryotic cells: Mitochondria are found in eukaryotic cells (not prokaryotic cells) which have a diameter in the range. Thus, each mitochondrion has about 1/100 to 1/10 the diameter of the whole cell and hence about 1/10^6 to 1/10^3 the volume of the whole cell.
The total volume of the mitochondria depends on the number of mitochondria as well. It could be as large as 1/5 of cell volume.
Comparison with wavelengths of light and implications for visibility under microscopes
The wavelength of visible light is in the range , which is at the lower end of the diameter range for mitochondria. Thus, mitochondria can be viewed with light microscopes (whose resolution is limited to ) but their internal structures cannot be clearly identified. Electron microscopes need to be used to study the structure of mitochondria well.
The mitochondrion has the following structural components:
|outer mitochondrial membrane|
|inner mitochondrial membrane|