Question

After Greg LeMond won his first Tour de France, he was shot in the back during a hunting trip. This accident seemed to trigger a downfall of his health, even though he went on to win two more Tour de France races, due to a ripple in the electron transport chain and mitochondria. Explain this concept of the electron transport ripple and whether or not the gun shot led to LeMond’s ultimate diagnosis of “Mitochondrial Myopathy.”

Answer 1

Greg Lemond is an american racing cyclist who was diagnosed with a muscle biopsy which revealed ragged red fibers indicating mitochondrial myopathy. The genes involved in mitochondrial disease normally make protein that work inside or on the mitochondria. These proteins forms the assembly line that utilizes different metabolites in the form of carbohydrates, fats, etc in order to produce ATP via oxidative phosphorylation which requires the presence of oxygen and occurs inside the inner membrane of mitochondria. Proteins inside the mitochondria are organized into five complexes namely I, II, III, IV and V and two mobile carriers CoQ and cytochrome c. Their role is to extract energy from the electrons to produce ATP. Complex I to IV shuttle the electrons and so are called electron transport chain while complex V actually produce ATP, so called ATP synthase. The deficiencies of one or more of these complexes is the prime cause of mitochondrial disease characterized by muscle weakness, exercise intolerance, hearing loss, trouble with balance and coordination, seizures, etc. The proper functioning is attributed to translation of the proteins of the oxidative phosphorylation pathway, imported into the mitochondria and inserted in the inner membrane. Any defect in this entire sequence of events may cause serious complications called electron transport ripple which may lead to mitochondrial myopathy.

When a cell contain a defective mitochondria, there is no production of ATP, as a result the cell remain deprived of ATP. In addition to this, the defective mitochondria can also accumulate unused fuel molecules and oxygen which can pose devastating effects. In such cases, excess of this fuel molecules are used to make ATP that produces certain harmful byproducts like lactic acid. The excessive accumulation of lactic acid inside a cell causes lactic acidosis that is associated with muscle fatigue. The unused oxygen in the cell may be converted to reactive oxygen species including the free radicals. These free radicals may destroy DNA, proteins, fatty acids and all biomolecules and in turn cells are destroyed. ATP derived from mitochondria serves in muscle contraction and generation of action potential. So mitochondrial defects affect both muscle and nerve cells. The combined effects of ATP deprivation and accumulation of toxic harmful substances in the cells may be the potential cause of symptoms of mitochondrial myopathy.