Disadvantages Of Mitochondrial Dna

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Until recent years, the mitochondrial genome, located in the mitochondrion, and the genetic information encoded by it have been given little attention. However, recently it became apparent that the mitochondrial genome, despite its small size, is crucial for the study of human evolution and disease, as mtDNA mutations lead to some serious diseases.

Mitochondrial DNA is just a small part of the genome. It is a double-stranded circular DNA molecule encoding sequences of 13 polypeptides, which are critical to respiration, as well as 24 RNA. MtDNA consists of 16,569 nucleotide pairs, 44 percent of MtDNR are G+C. DNA chains differ from each other in nucleotide composition: in the heavy chain, there is relatively more guanine, while in the
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The remaining 13 genes encode polypeptides which are synthesised in mitochondrial ribosomes. All of the 13 polypeptides are respiratory complex subunits, which are involved in oxidative phosphorylation, ensuring the production of adenosine triphosphate (ATP). The whole complex consists of approximately 100 polypeptides. Nuclear DNA encodes most of the polypeptides which are synthesised in the cytoplasm and then transported into the mitochondria. Unlike human nuclear DNA, human mitochondrial DNA is very compact: about 93 percent of mtDNA sequence is capable of encoding, all 37 mitochondrial genes are without introns. Some genes coding sequences overlap. Several genes have no termination codons.

Due to the large size of the human nuclear genome, most of the mutations occur in nuclear DNA sequences. In contrast, the mitochondrial genome is small (about 1/200 000 nuclear genome size), so the mutation should occur less frequently. Unlike the nuclear genes, there are thousands of the copies of mitochondrial genes in each human somatic cell. For some cells such as the brain or muscle, very intense oxidative phosphorylation is required, and hence they have larger amounts of mitochondria. Typically approximately 99.9 percent of human mtDNA is identical (homoplasmy). If the mutation happens and it spreads in the population, there will be two very common mtDNA genotypes
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