With recent news about three parent zygotes created to replace defective maternal mitochondrial DNA, you might be wondering "What is a mitochondrion?"

What Are Mitochondria?

Mitochondria are the cellular organelles that manufacture most of the energy that our cells need to function. Cellular respiration, series of reactions that take place within the mitochondria, complete the process of turning food energy into ATP energy that can be used in many different cellular reactions.

ATP is like the “cellular Euro” of energy forms. It can be used to drive anabolic reactions within the cell. Therefore the mitochondria are often referred to as the “power houses” of our cells (Campbell & Reece).

What Is Mitochondrial DNA?

Most of the deoxyribonucleic acid (DNA) within cells of eukaryotic organisms is confined to the membrane-bound nucleus. The majority of cellular organelles do not have their own DNA. The fact that mitochondria do contain DNA is part of the evidence that leads scientists to believe that the ancestors of this organelle were once independent prokaryotic cells.

The DNA within mitochondria is called mtDNA, and each mitochondrion is estimated to contain 2-10 copies. In the cells of modern day organisms, the genes that were originally found in that symbiotic prokaryotic cell are now also present in our nuclear DNA, having since been transferred to the eukaryotic nucleus through the course of evolution (Campbell & Reece).

Maternal mtDNA

Among multicellular organisms like us, nearly all of the mtDNA in a fertilized egg (zygote) is inherited from the female parent. Our mitochondrial DNA contains about 16,500 DNA base pairs representing 37 genes, just a fraction of the total DNA within a cell. However, since most of our ATP is generated by the mitochondria, the role of this organelle, and the DNA that it contains, is absolutely vital to the viability of every cell in our body. There are several genetic conditions related to abnormalities in mitochondrial genes (Campbell & Reece 2005).

Inherited Mitochondrial Mutations

Inherited changes in mitochondrial DNA (those passed on through the egg of the mother) can cause problems relating to growth, development, and function of the body's systems. These mutations disrupt the mitochondria’s ability to generate ATP energy and therefore often involve multiple organ systems, particularly the organs and tissues that require more energy (such as the heart, brain, and muscles).

Although the health-related implications of inherited mitochondrial DNA mutations vary widely, some frequently observed problems include muscle weakness and wasting, difficulties with movement, diabetes, kidney failure, heart disease, dementia, hearing loss, and abnormalities involving the eyes and vision (National Library of Medicine).

Somatic Mitochondrial Mutation

A buildup of noninherited (somatic) mutations in the mitochondrial DNA have been associated with an increased risk of certain age-related disorders such as heart disease, Alzheimer disease, and Parkinson disease. Additionally, research suggests that the progressive accumulation of these mutations over a person's lifetime may play a role in the normal process of aging (National Library of Medicine).

More Information

See the website Science Prof Online for more articles on genetics and deoxyribonucleic acid (DNA) or look to the Suite 101 articles Thee Parent Embryo & mtDNA and Forensic DNA.

Sources

BBC News (2008) Three Parent Embryo Formed In Lab.

Campbell & Reece, Biology, 7th Edition, Pearson Publications.

Leakey, R. E., and Lewin, R. (1978) People of the Lake: Mankind and its Beginning. Anchor Doubleday.

National Library of Medicine, “Mitochondrial DNA" National Institute of Health, US Government