Mitochondria
(1) Nucleolus
(2) Nucleus
(3) Ribosomes
(4) Vesicle
(5) Rough endoplasmic reticulum (ER)
(6) Golgi apparatus
(7) Cytoskeleton
(8) Smooth ER
(9) Mitochondria
(10) Vacuole
(11) Cytoplasm
(12) Lysosome
(13) Centrioles within centrosome
Mitochondria [1] are organelles, or parts of a cell.
Their main job is energy conversion. They oxidise glucose to produce energy that the cell can use. The process is called cellular respiration, which makes ATP, a molecule which the cell can use as a source of energy. The stage which gives ATP is called the citric acid or Krebs cycle.[2]
In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signalling, cellular differentiation, cell death, as well as the control of the cell division cycle and cell growth.[3]
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[change] DNA
It is thought that mitochondria were once independent bacteria, and became part of the eukaryote cell by endosymbiosis.[4]
Although most of a cell's DNA is contained in the cell nucleus, the mitochondrion has its own independent genome, called mDNA. Further, its DNA shows substantial similarity to bacterial genomes.[5]
[change] Inheritance
Mitochondria divide by binary fission similar to bacterial cell division. In single-celled eukaryotes, division of mitochondria is linked to cell division. This division must be controlled so that each daughter cell receives at least one mitochondrion. In other eukaryotes (in humans for example), mitochondria may replicate their DNA and divide in response to the energy needs of the cell, rather than in phase with the cell cycle.
An individual's mitochondrial genes are not inherited by the same mechanism as nuclear genes. The mitochondria, and therefore the mitochondrial DNA, usually comes from the egg only. The sperm's mitochondria enter the egg, but are marked for later destruction.[6] The egg cell contains relatively few mitochondria, but it is these mitochondria that survive and divide to populate the cells of the adult organism. Mitochondria are, therefore, in most cases inherited down the female line, known as maternal inheritance. This mode is true for all animals, and most other organisms. However, mitochondria is inherited paternally in some conifers plants, though not in pines or yews.[7]
A single mitochondrion can contain 2–10 copies of its DNA.[8] For this reason, mitochondrial DNA usually is thought to reproduce by binary fission. However, there is some evidence that animal mitochondria can undergo recombination.[9] If recombination does not occur, the whole mitochondrial DNA sequence represents a single haploid genome, which makes it useful for studying the evolutionary history of populations.
[change] Related pages
[change] References
- ↑ Greek mitos, a thread + khondrion, granule
- ↑ Henze K. & Martin W. 2003. Evolutionary biology: essence of mitochondria. Nature 426: 127–8.
- ↑ McBride HM, Neuspiel M, Wasiak S (2006). "Mitochondria: more than just a powerhouse". Curr. Biol. 16 (14): R551. doi:10.1016/j.cub.2006.06.054. PMID 16860735.
- ↑ Lake, James A. Evidence for an early prokaryote symbiogenesis. Nature 460 967–971.
- ↑ Andersson SG, Karlberg O, Canbäck B, Kurland CG (January 2003). "On the origin of mitochondria: a genomics perspective". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 358 (1429): 165–77; discussion 177–9. doi:10.1098/rstb.2002.1193. PMC 1693097. PMID 12594925.
- ↑ Sutovsky, P., et al. (1999). "Ubiquitin tag for sperm mitochondria". Nature 402: 371–372. doi:10.1038/46466. Discussed in Science News.
- ↑ Mogensen HL (1996). "The hows and whys of cytoplasmic inheritance in seed plants". American Journal of Botany 83 (3): 247. doi:10.2307/2446172.
- ↑ Wiesner RJ, Ruegg JC, Morano I (1992). "Counting target molecules by exponential polymerase chain reaction, copy number of mitochondrial DNA in rat tissues". Biochim Biophys Acta. 183 (2): 553–559. PMID 1550563.
- ↑ Lunt DB, Hyman BC (15 May 1997). "Animal mitochondrial DNA recombination". Nature 387 (6630): 247. doi:10.1038/387247a0. PMID 9153388.
