Mitochondrial DNA
As mitochondrial DNA, mtDNA short, sometimes referred to as Chondriom, mostly circular, double-stranded DNA is referred to in the interior (matrix) of the mitochondria. The mtDNA was discovered in 1963 by Margit MK wet and Sylvan wet with electron microscopy and 1964 by Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz basis of biochemical measurements.
The human mtDNA is 16,569 bp of 37 genes (13 mRNAs ( encode protein subunits of the respiratory chain complex I, III, IV and V), 22 tRNAs and two rRNA ( 12S and 16S rRNA) ). The mtDNA has 100-10,000 copies per cell with 10-15 molecules per mitochondrion.
Properties
MtDNA multicellular organisms is usually organized in a circular, i.e., it consists of a closed ring to a double-stranded DNA. In many single-celled organisms and also in some multicellular organisms (eg, some species of Cnidaria ), but also linearly organized mtDNA was detected (eg, in the ciliate Tetrahymena or the green alga Chlamydomonas reinhardtii ). The ends of this linear mtDNA form of telomerase -independent telomere with different replication mechanisms, which makes them interesting objects of research, as with linear mtDNA find many pathogens among the protists. Although a mtDNA - specific DNA polymerase is present ( nuclear encoded Pol γ ), the existence of a separate mtDNA allows the mitochondria not, regardless of the cell in which they are located, to divide and multiply. However, the pitch frequency of the mitochondria is only indirectly a function of the cell. On the mtDNA contains some, but not all, of the genes for the enzymes of the respiratory chain as well as genes that are responsible for the structure and reproduction of the mitochondria. However, the genes of more than 90 % of the proteins that comprise a mitochondrion, localized in the nucleus and synthesized in the cytoplasm of the cell. The finished proteins after transcription and translation using a translocation complex (TOM / TIM) on the two mitochondrial membranes imported into the interior of the mitochondria.
MtDNA is organized within the matrix in the so-called Nucleoiden, a cell nucleus equivalent, as is also found in prokaryotes. These include both the nucleic acid and proteins.
Origin
The presence of an own DNA is unique among organelles of the animals, in plants, the chloroplasts have the same property. This is the starting point for the endosymbiont theory that states that mitochondria and chloroplasts were originally separate organisms that were incorporated in the course of evolution in animal or plant progenitor cells and now take over certain tasks for these cells. Further evidence for this are that mitochondria are about the same size as small bacteria, a circular DNA have and are surrounded by two membranes. Also, the protein synthesis machinery (eg ribosomes) of mitochondria is very similar to that of prokaryotes. Moreover, mtDNA contains, similar to bacterial DNA and histones hardly no introns.
Heredity
In genealogy and anthropology inheritance of mtDNA plays a major role. One hand this has to do with the fact that mitochondria are maternally only, that is passed in many organisms only from the mother to the offspring. The mitochondria of the sperm are located in the neck, which participates only partially in the merger of the sperm head with the egg. In addition, the egg emits substances that dissolve the mitochondria of the sperm. More specifically, they are marked with ubiquitin and then degraded. In addition, mtDNA mutates at a very constant rate, so you can say relatively accurately how close ( in terms of time ) two tribes are related, ie, when separated the precursor of these strains. In anthropology thus could be shown that the American aborigines is most closely related to the indigenous people of Eurasia (ie descended from a common ancestor ); also hypotheses about the origins of modern humans ( Mitochondrial Eve) could be confirmed. The 2005 launched the Genographic Project, examines which genetic material of people on all continents with the aim to gain more detailed knowledge about the relationships of the different populations as well as the end of the colonization of Earth by Homo Sapiens, these properties of mtDNA makes advantage.
A few years ago the so-called paternal inheritance of mtDNA was detected in several animal species and in one case in humans. You obviously seem to be relatively rare ( in mice, the rate of 1:10,000 ) and ensures that male mtDNA is transmitted to the offspring. The exact mechanism is not yet clear; it lacks even reliable figures, the frequency with which this form of inheritance in humans. A single case is known since 2002 that a special peculiarity / mutation of mtDNA is inherited from the father to his son: During the blood- mtDNA was inherited from the mother, 90 % of muscle mtDNA were inherited from the father. After further investigation generally far ( as of 2009), it is assumed that this particular finding the assumption that mitochondria can be inherited in humans only maternal, does not contradict; methodological problems of analysis could pretend paternal inheritance.
Neanderthal mtDNA
Svante Pääbo succeeded in 2008, the mitochondrial genome of a Neanderthal (Homo neanderthalensis ), who lived 38,000 years ago, complete with a hitherto unattained accuracy of sequencing.