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Virtually everything that human cells need to maintain health requires energy. Each cell contains hundreds to thousands of mitochondria, and each mitochondrion contains multiple copies of mitochondrial DNA (mtDNA). Mitochondrial proteins take food molecules and combine them with oxygen to create chemical energy. This chemical energy produced by the mitochondria through the cellular respiration process is called adenosine triphosphate (ATP) (see Figure 1).
Generally the duration of life varies inversely with the rate of energy expenditure during life. Bio-gerontologist Denham Harman, PhD, the “father of the free radical theory of aging,” once suggested that mitochondria are the crucial component of cells whose rate of decline dictates the overall rate of aging.1 In addition to supplying cellular energy, mitochondria are involved in a range of other processes such as signaling, cellular differentiation and cell death, as well as controlling the cell’s cycle and growth.2
In human cells and eukaryotic cells in general, DNA is found in two cellular locations: inside the nucleus and inside the mitochondria. The generation of reactive oxygen species (ROS) such as superoxide anion, hydrogen peroxide and hydroxyl radicals as by-products of mitochondrial oxidative phosphorylation (see Figure 2) damages mitochondrial macromolecules including the mtDNA, leading to deleterious mutations.
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