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Mitochondrial Functions and how Mitochondrial Diseases Develop

The mitochondria generate energy by burning the hydrogen trapped in the carbohydrates and fats of our food with the oxygen that we breath to generate water and a chemical energy carrier adenosine triphosphate (ATP). This is accomplished by the process called oxidative phosphorylation (OXPHOS). During OXPHOS, electrons are passed through a series of multi-subunit enzyme complexes located within the mitochondrial inner membrane. The passage of electrons through the Electron Transport Chain is used to pump protons across the mitochondrial inner membrane, creating an electricochemical gradient across the membrane. This proton gradient is then used to produce ATP, our cells' source of energy.

As a toxic by product of burning hydrogen with oxygen, the mitochondria produce most of the oxygen radicals generated in our bodies, known collectively as reactive oxygen species (ROS). These ROS, in turn, can damage the mitochondrial and the mitochondrial DNA (mtDNA) contained within the mitochondrion. Without good mtDNA the damaged mitochondria can not be repaired and mitochondrial energy production declines.

Since cells with defective mitochondria will malfunction, they would compromise the function of the surrounding tissue. Thus, cells with defective mitochondria must be eliminated. This is accomplished through a self-destruct switch built into the mitochondrion, the mitochondrial permeability transition pore (mtPTP). When mitochondrial energy metabolism declines too much and/or oxidative damage becomes too great, then the switch is thrown and the defective mitochondria and surrounding cells are destroyed by programmed cell death (apoptosis). While this process removes the offending cell, eventually too many cells are lost. Then the tissue and organ can no longer do their job and disease symptoms arise.