An Overview of Human Mitochondrial Genetics

Mitochondria are organelles found in most eukaryotic cells. Their most well-known function is generating energy by providing the cell with adenosine triphosphate (ATP), which constitutes a major source of biochemical energy. Besides being the cell's main energy providers, they also play a part in other processes, such as the control of the cell cycle and cell growth. On top of this, they are suspected to have a role in several diseases, as well as the aging process.

One very special characteristic of mitochondria is that they possess their own genome, independent from the chromosomal DNA found in the cell’s nucleus. This mitochondrial DNA looks quite similar to bacterial DNA, and this similarity has provided strong support for the ‘endosymbiont theory’, the theory that the mitochondria originally were bacteria who invaded eukaryotic cells and adapted to life there.

In contrast to the regular genome, the mitochondrial genome is inherited solely from the mother. It is a circular molecule and a large percentage of it codes for proteins. This mean that in contrast to chromosomal DNA, most mitochondrial DNA mutations will lead to problems.

The field of human mitochondrial genetics occupies itself with the study of the human mitochondrial genome. Through studying this, our understanding of several important aspects of human biology may increase. The most pursued topics in human mitochondrial genetics at the moment are:

• Fundamental knowledge: by researching the process of mitochondrial replication, fundamental knowledge concerning the processes of replication, DNA repair, transcription and translation can be gained. A greater understanding of these processes can subsequently prove helpful in understanding the human genome in its entirety.

• Mitochondrial diseases: many health conditions, ranging from asymptomatic to fatal ones, are influenced by inherited mitochondrial DNA mutations. A specific characterization of mitochondrial diseases is actually quite hard as several mutations can cause the same problems, and, vice versa, one single mutations can have a myriad of effects. Furthermore, some conditions manifest themselves at or even before birth, whereas other know a late onset. Besides, one cell can contain several mitochondria, each with its own mutations. Mitochondria are suspected to play a role in many well-known health problems, including Parkinson’s disease, Alzheimer’s disease, cardiovascular issues, cancer, and so on. Understanding the mitochondria can elucidate the processes behind these conditions and might even contribute to possible treatments.

• Human evolution: another interesting aspect of human mitochondrial genetics, is that through studying mitochondrial DNA, the maternal lineage of mankind can be reconstructed. To learn more about the quest for ‘mitochondrial Eve’, see The Link Between Mitochondrial DNA and Human Evolution.

• Falkenberg, M., Larsson, N.G. & Gustafsson, C.M. (2007). DNA replication and transcription in mammalian mitochondria. Annual Review of Biochemistry. 76, pp. 679 – 699.
• McBride, H.M.; Neuspiel, M. & Wasiak, S. (2006). Mitochondria: more than just a powerhouse. Current Biology. 16(14), R551.
• Schapira, A.H.V. (2006). Mitochondrial disease. The Lancet. 368(9529), pp. 70 – 82.
• Taylor, R.W. & Turnbull, D.M. (2005). Mitochondrial DNA mutations in human disease. Nature Review Genetics. 6, pp. 389 – 402.