Why is Mitochondrial DNA Important?

Mitochondria are tiny organelles that are often referred to as the energy powerhouses of cells or our body's batteries. Their prime function is to take in the sugars that have been converted from the food we eat, and turn them into a form of energy that cells can use. Other functions include regulation of cellular metabolism, regulation of cell membrane potential, and steroid synthesis. Each mitochondrion spans 16 kilobases encoding 37 genes.

Mitochondrial DNA is important for a number of reasons. 13 of its 37 genes are involved in the process known as oxidative phosphorylation. This is the metabolic pathway that produces adenosine triphosphate (ATP), the main energy source of the cell. The remaining 24 genes are involved in the creation of transfer RNA (tRNA) and ribosomal RNA (rRNA) which help to turn amino acids into proteins.

Mitochondrial DNA also appears to be important for a healthy body as there are a number of genetic disorders associated with changes in mitochondrial genes. Some of these genetic disorders are: -

Cancers - mitochondrial DNA, like nuclear DNA is subject to somatic mutations. These are faults that occur during an individual's lifetime and are not passed down to subsequent generations. Mitochondrial DNA mutations have been found in various cancers including breast, colon, and liver cancers.

Leber hereditary optic neuropathy (an inherited form of vision loss) - four mitochondrial genes, MT-ND1, MT-ND4, MT-ND4L, and MT-ND6 have been linked with this condition. It appears that changes in these genes affect the generation of ATP, although it is unknown why the effects of the mutations are limited to the optic nerve.

Nonsyndromic deafness (hearing loss which is not associated with any other syndromes) - mutations in two mitochondrial genes, MT-RNR1 and MT-TS1 are linked to this disorder. The genes are involved in making different types of RNA.

Mitochondrial DNA is also enjoying increasing importance in forensic science. Criminals can be foiled as it is also used in DNA fingerprinting. It has several useful attributes;-

• As there are hundreds of mitochondria in each cell, there are hundreds of genes, thereby providing forensic scientists with abundant source material.
• Mitochondria are well protected in the cell, and so don't necessarily suffer as much degradation as nuclear DNA.
• As mitochondria are passed solely down the maternal line, any maternal relative can be used as a reference sample. Though this can be a disadvantage in that it is not a unique identifier. This is because relatives within that maternal lineage will share the same mitochondrial DNA.