All was for the best when, 1.8 billion years ago, cyanogen bacteria appeared. These cyanobacteria are the oldest known fossils.They threw out oxygen into our atmosphere. This "pollution" drastically changed life on our planet
Nitrogen -----------
dioxide --------------------------
Hydrogen --------------
A very very long time ago, around 2 billion years ago, some very primitive bacteria lived happily breathing nitrogen, carbon dioxide and hydrogen. All was for the best.
Nitrogen ----------------------
Carbon dioxide -------------------
Hydrogen -------------------------
As most primitive bacteria were not able to metabolise oxygen : their proteins and chromosomes were completely burnt
cyanogen bacteria
Mitochondria are cellular organelles dedicated to transforming the gigantic source of energy represented by Oxygen into a "soft energy" : ATP. Thanks to mitochondria we only transform into heat a minute fraction of the energy produced by oxidations, and store it for our muscles, our heart, our kidneys, our thoughts, and all the many functions of our bodies.
Only some bacteria and paucicellular beings from mud and still water survived. They mutually infected one another and were infected by the cyanogen bacteria. Resistant bacteria, able to metabolise oxygen, are the ancestors of our mitochondria.
The mitochondria which live in the cytoplasm of our cells only bear a vague resemblance to their bacterial ancestors : Their circular chromosome.
Their DNA does not use the same genetic code as our other chromosomes, and part of it has a triple helix.
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Mitochondrial transporters
Mitochondria & ATP