Life on Earth has existed for about 4 billion years now, and 2 billion that single cells without nuclei have appeared. There were archaea and bacteria, two types of microorganisms close but with different composition.
Some bacteria then, during evolution, invaded the archaea which, in turn, took advantage of it. These bacteria have evolved into mitochondria within our cells. This association has made it possible to build our cellular “nucleus”, where our precious DNA will be stored.
There are two branches: prokaryotes (living beings with a single cell without nucleus) and eukaryotes (living beings with one or more cells with nuclei, including humans).
Eukaryotes contain bacterial mitochondria with bacterial DNA. So, we have bacteria DNA in our cells.
Only mothers can transmit these mitochondria to us. To better understand how it works, we need to look more closely at our sexual reproduction. For a naturally way we need a male and a female.
We transmit, during our reproduction, our genes but also our mitochondria. Although parents mix their genes, but they avoid mixing their mitochondria. With us, mankind, and most living beings, it is the mother who transmits this precious roommate of our cells.
But what are these mitochondria used for and where are they located? Our mitochondria are found in our cells in the cytoplasm, the contents surrounding the nuclei. They make it possible to produce ATP (adenosine triphosphate), the energy necessary for the functioning of our cells. They also work for homeostasis, the balance of our body and its functions like temperature, react to stressors and manage cell waste. They are also part of groups that deal with the programmed death of our cells. But beware! In our body nothing works alone. Everyone collaborates, the mitochondrion never acts alone.
How is this ATP produced and in which case it can be used? Most of this energy comes from what we call the metabolism of glucose and fatty acids by our mitochondria. The goal is to transform the glucose absorbed in our food using enzymes. Enzymes are molecules that speed up reactions. This is made possible by a mechanism called oxidative phosphorylation.
Illustration of oxidative phosphorylation
This energy can be used by the cells but is not the single way. There is a link with the production of heat from the mitochondria and therefore our homeostasis. In fact, more the production of heat is higher, more the ATP production is lower. This characteristic may be heritable in certain populations according to the study by Ruiz-Pesini et al. 2000. Residents of cold climates are therefore more likely to have inherited mitochondria whit less ATP produce and therefore more heat.
Another interesting fact, we saw previously that only women within our species can transmit mitochondria. In fact, we also find ATP in the sperm, in fact, some mitochondria. Their function is to provide energy for a long sprint for these swimmers to reach the finish line, they will be eliminated once the winner has crossed the egg barrier. Only the mitochondria brought by the mother are thus considered. If these male mitochondria do not work well, what happens? Well, little swimmers have misfires, because there will not have enough ATP and the male fertility rate will be reduced.
These mitochondria have effects at different stages of our evolution, but also throughout our body.
We talked about their reactions to stressors. There can be many causes, such as nutrient deprivation, which damages cells and DNA, and thus shortens life expectancy.
Finally, for the management of "waste", we can compare our mitochondria to recycling factory. If a dysfunction occurs following, for example, a tumor, an accumulation of this "waste" around our cells affects their living environment, but also their good communication with its neighbors.
Thus, we harbor bacterial DNA in our own cells, the result of an evolutionary symbiosis of several species billions of years ago.
Our health depends on our mitochondria and vice versa. It is therefore important to take care of these inhabitants of our cells so that our bodies function properly.
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