The nitro group is thus added as an ester C−O−NO2 and water is produced. This is different from an electrophilic aromatic substitution reaction in which nitronium ions are the electrophile. The addition of glycerol results in an exothermic reaction (i.e., heat is produced), as usual for mixed-acid nitrations. If the mixture becomes too hot, it results in a runaway reaction, a state of accelerated nitration accompanied by the destructive oxidation of organic materials by the hot nitric acid and the release of poisonous nitrogen dioxide gas at high risk of an explosion. Thus, the glycerin mixture is added slowly to the reaction vessel containing the mixed acid (not acid to glycerin). The nitrator is cooled with cold water or some other coolant mixture and maintained throughout the glycerin addition at about 22 °C (72 °F), hot enough for esterification to occur at a fast rate but cold enough to avoid runaway reaction. The nitrator vessel, often constructed of iron or lead and generally stirred with compressed air, has an emergency trap door at its base, which hangs over a large pool of very cold water and into which the whole reaction mixture (called the charge) can be dumped to prevent an explosion, a process referred to as drowning. If the temperature of the charge exceeds about 30 °C (86 °F) (actual value varying by country) or brown fumes are seen in the nitrators vent, then it is immediately drowned.
Genomics
Mutations in mitochondrial DNA (mtDNA) and over 30 genes in nuclear DNA (gene SURF1 and some COX assembly factors) have been implicated in Leigh disease.Disorders of oxidative phosphorylation, the process by which cells produce their main energy source of adenosine triphosphate (ATP), may be caused by mutations in either mtDNA or in nuclear encoded genes. The latter account for the majority of Leigh disease, although it is not always possible to identify the specific mutation responsible for the condition in a particular individual. Four out of the five protein complexes involved in oxidative phosphorylation are most commonly disrupted in Leigh syndrome, either because of malformed protein or because of an error in the assembly of these complexes. Regardless of the genetic basis, it results in an inability of the complexes affected by the mutation to perform their role in oxidative phosphorylation. In the case of Leigh disease, crucial cells in the brain stem and basal ganglia are affected. This causes a chronic lack of energy in the cells, which leads to cell death and in turn, affects the central nervous system and inhibits motor functions. The heart and other muscles also require a lot of energy and are affected by cell death caused by chronic energy deficiencies in Leigh syndrome. Mitochondrial DNA mutations
Mitochondria are essential organelles in eukaryotic cells. Their function is to convert the potential energy of glucose, amino acids, and fatty acids into adenosine triphosphate (ATP) in a process called oxidative phosphorylation. Mitochondria carry their own DNA, called mitochondrial DNA (mtDNA).