Dancing Between Purity and Pollution
Mitochondria can allow life or kill us. Mitochondrial DNA has only 37 genes. From those 37 genes comes just 13 proteins. Those 13 proteins code for the electron chain transport complexes. The remainder of the genes code for tRNA. Mitochondria also cant grow outside the cell. They require the 30,000 genes in the nucleus to make up another 1500 proteins for them to function. Mitochondrial DNA and nuclear DNA have to have precise lock and key fit to generate energy production. If not, the cell eliminates itself by apoptosis (levee 19) fast. If It works well, this combination is naturally selected for future cell division to generate energy. Aging is quantified by how "leaky" our mitochondria are to free radicals at complex ones in electron chain transport. Their own DNA is adjacent to the first complex in electron chain transport. So the more leakage, the more damage is done to its DNA and energy production will fall. Moreover, that is the signal to make more mitochondria or undergo cell suicide! This first complex (NADH) is by far the most leaky to free radicals of all the complexes. This paradox of fate caused evolution to select for 10-20 copies of mitochondrial DNA in each cell to sustain energy production of an organ in question. So mitochondria can breathe life into us and end it based upon how many good mitochondria we have in a tissue.