Discrete structures floating in cytoplasm in the cells of our bodies have specialized functions that regulate cellular activity. These structures are called organelles and like the name implies, they are to the cell what organs are to the body. They keep the cell healthy and functioning well as programmed by our DNA. All except for one, that is. Mitochondria are different.
Mitochondria has its own DNA and it isn’t human. It’s more like an old infection. Mitochondria are the descendant of proteobacteria that invaded the cells of a common ancestor when life was new on the planet. The invasion was parasitic, as invading bacteria tend to be. Their mission was to hijack cellular glucose and metabolize for their own purpose, to nourish and expand the invading bacterial colony.
Different bacteria metabolize glucose in different ways. Disease causing bacteria produce cytotoxic metabolites that trigger an immune system response. Other bacteria have chemically benign metabolites. They are inconsequential parasites that hijack a little glucose and take up a little space. Other bacteria have metabolic processes that are beneficial to the host cell. They are symbiotic. The host cell is good for them and they are good for the host. Mitochondria have an endosymbiotic (a mutually beneficial arrangement in which one organism lives completely within another.) relationship with eukaryotic cells (complex cells like the kind we have) which is so successful, it saturates life on the planet today. Every life form, plant and animal, except for bacteria, has mitochondrial organelles in their cells and has for millions of years. It is likely the most important event in the evolution of life on the planet. Life forms that predate it have all been replaced by it. Every single one.
What makes mitochondria symbiosis so special is the way they metabolize glucose. Glucose is fuel for cells like gasoline fuel is for cars. Mitochondria boosts the energy released from metabolizing glucose by a factor of 27. Normal cellular metabolism is anaerobic. It builds an electrical potential across a synapse by charging the positive side with 4 hydrogen ions per molecule of glucose metabolized. Mitochondria metabolize glucose aerobically. It borrows electrons from oxygen in water; releasing hydrogen ions ate the rate of 28 per glucose molecule metabolized. A quantum leap in energy production compared to the cellular method.
In exchange for mitochondrial energy, host cells provide mitochondria with: Warm cytoplasm to live in; all the glucose they want; Immunity from immune system attacks; and protection from other invaders (which the immune system will attack.) These offers are guaranteed as long breath fills the lungs and blood flows in the veins.
Read also: Mitochondria structure and functions
