Mitchondrial DNA in Aging and Disease.
Mitochondria can be found in all human cells. They are the home to many complex energy producing biochemical pathways in cellular respiration such as the Krebs cycle and the Electron Transport Chain. One interesting feature of mitochondria is that mitochondria have DNA. In our "Understanding the Human Genome" class, we have focused mainly on the portion of the Human Genome in the nucleus. However, not much attention has been paid to a section of the genome found in the mitochondrion: mitochondrial DNA, (or mtDNA). MtDNA is only 16,569 base pairs in length, less than 1/300,000th of the entire human genome (Miller), yet mtDNA it has some properties that carry important implications. In this essay, I would like to discuss some important properties of mitochondrial DNA, and the implications of these properties on forensic DNA testing, on eukaryotic evolutionary history, and on human aging and disease. .
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Properties of Mitochonria.
Although mtDNA is very short in length, it is very efficient: the percentage of the encoding regions in mtDNA is quite high. It codes for the ribosomal RNA and the transfer RNA that are used in the mitochondria, as well as thirteen polypeptides found in the electron transport chain, such as the transfer proteins and ATP synthase. Replication of mtDNA is performed by a special form of DNA polymerase called DNA polymerase gamma. Interestingly, DNA polymerase gamma does not have any proof reading during mtDNA replication. Also, mitochondria do not have any of the efficient repair mechanisms that the nucleus has for nuclear DNA replication. Because of the lack of proof reading and of efficient repair mechanisms, the mutation rate in mtDNA is about ten times that of nuclear DNA (Life Extension, 2). .
This higher mutation rate of mtDNA has interesting implications. First of all, mtDNA can be used to track human evolution and migration patterns whereas nuclear DNA could not be used because the time scale for nuclear DNA mutations is too long.
