Difference between revisions of "Mitochondrion"

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.

Summary

Item Value
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 ${\displaystyle 0.5-1.0\mu m}$ 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
Cellular differentiation
Cell growth
Cell death
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.

Size

Diameter and volume

The diameter of mitochondria is in the range ${\displaystyle 0.5-1.0\mu m}$ (microns), where one micron is ${\displaystyle 10^{-6}m}$.

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 endosymbiotic theory of mitochondrial origin).

Comparison with eukaryotic cells: Mitochondria are found in eukaryotic cells (not prokaryotic cells) which have a diameter in the ${\displaystyle 10-100\mu m}$ 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 ${\displaystyle 0.4-0.7\mu m}$, 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 ${\displaystyle 0.2\mu m}$) but their internal structures cannot be clearly identified. Electron microscopes need to be used to study the structure of mitochondria well.

Physical structure

The mitochondrion has the following structural components:

Component Thickness Volume
outer mitochondrial membrane
intermembrane space
inner mitochondrial membrane
cristae
mitochondrial matrix