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.

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 mitochond

However, mtDNA diseases such as mitochondrial myopathy or KSS are relatively rare. MtDNA mutations can be involved with other more common diseases, such as some forms of diabetes. In fact, about two percent of patients with type II (adult onset) diabetes have known mtDNA mutations, often associated with deafness (Schon, 3). Also, diabetes is a very common secondary symptom of many mtDNA-related diseases. Aside from diabetes, mutations in mtDNA are thought to be involved in more common diseases such as Alzheimer’s, Parkinson’s and Huntington’s, diseases that are caused by degraded brain function. Specifically, patients with Alzheimer’s disease do not have enough of the enzyme choline astransferase, which is a neurotransmitter involved with memory (Warren). Researchers discovered that patients with Alzheimer’s disease had multiple deletions at mtDNA 4977, which is part of the genes for COI and COII cytochrome c oxidase, enzymes that function in the electron transport chain (Warren). In these patients, the level of these enzymes in the brain is greatly reduced (Warren). Researchers have also observed that Huntington’s disease and Parkinson’s disease patients contained an abnormally high number of deletions at that same mtDNA site. Although the exact mechanism of these three diseases are not fully understood, it is nevertheless interesting, that mtDNA mutations, caused by the overproduction of free radicals (Warren) are involved with these diseases, and that these diseases follow the trends of mtDNA related diseases: onset of symptoms relatively late in life, and symptoms mimicking the symptoms of aging.

In 1960, nuclear physicists and radiation biologists believed that mutations in the nuclear DNA caused aging in humans. However, this was later deemed unlikely because of the numerous repair mechanisms and in turn the relative immutability for nuclear DNA (Life Extension, 1). Later on in the 1960’s, a man named Denham Harman proposed his Mitochondrial Theory of Aging, and claimed that aging was caused by mtDNA which was damaged by free oxygen radicals, or molecules with Oxygen with a highly reactive unpaired electron.

Some topics in this essay:
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