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Bacteria are prokaryotes. Animal cells, fungi and plants are eukaryotes. Prokaryotes tend to be acellular and lack nuclei, while eukaryotes strive towards multicellularity and specialization, and have highly organized nuclei. The life objectives of eukaryotes require lots of energy in the form of ATP.
Back in the mists of time, millions of years ago, bacteria took up permanent residence inside eukaryotes in a commensal or mutualistic relationship. The bacteria would get permanent shelter and nutrients, and the eukaryotic cells would get a permanent continuous safe supply of ATP energy in the form of between 500 and 100,000 bacteria living stably within each eukaryotic cell. These bacteria would be renamed mitochondria. (In plants they are called chloroplasts).
The mitochondria have their own DNA genome and reproduce both in an autonomous way inside each cell as well as in a manner performed in concert with a diplomatic relationship with the nucleus. Your mitochondria come almost exclusively from your mother, and this may be part of the driver for so-called maternal imprinting, the fact that a mother leaves her mark on offspring more than the father does. Mammals reproduce sexually, when sperm and egg fuse. An average human ovum has about 100,000 mitochondria. At fertilization, the midpiece of the spermatozoa, but not the head or the tail, enters the ovum. The midpiece has about 750 mitochondria. Thus if all your mitochondria don’t come from your mother, more than 99 percent did.
The mitochondria are mere dots within each cell, barely visible, but their presence within us may have helped drive evolution of our species to its sophisticated present form. The Liliputian here is the Brobdingnagian: mere dots within us, but they are our essence.
Over millennia, the intimacy between eukaryotes and their mitochondria grew. While the mitochondrial genome became smaller than those of ancestor bacteria, it also added new genes for servicing its master. Mitochondria took on roles not only of providing ATP but of caretaker functions. Mitochondria began to secrete “tune-up” peptides that optimized metabolism and organ function. Mitochondrially-derived peptides (MDPs) are tonic and trophic factors that restore our health.
Although we rely innately on mitochondria for our survival, they ...