An article published in the journal “Nature” describes a study that investigated a key moment in the evolution, when cells acquired mitochondria (image ©Wikigraphists of Atelier Graphique). Researchers Toni Gabaldón and Alexandros Pitis of the Centre for Genomic Regulation, an international institute for biomedical research based in Barcelona, ​​Spain, conducted a study whose conclusions suggest that the acquisition of mitochondria came late in the evolution of cells.

Mitochondria are organelles found in the cells of all eukaryotes, the most complex among those existing in living beings. Mitochondria have their own DNA, which contains a variable number of genes depending on the species, just as the DNA of the cell nucleus. In humans, they’re inherited from the mother because the ones in the sperm are destroyed.

The mitochondria DNA is autonomous and has some characteristics different from the nuclear DNA. These characteristics and other similarities with bacteria have been seen as indications that these organelles evolved as autonomous organisms before being incorporated into cells. A research published in 2011 in the journal “Nature” showed evidence of a common ancestor between mitochondria and the bacteria of the R11 clade, part of the Alphaproteobacteria class.

The presence of mitochondria gave an evolutionary advantage to eukaryotes, which make up the most complex forms on Earth. The theory of the symbiosis that led to incorporate the mitochondria has the consensus of scientists but it’s not clear when this happened. To try to understand a crucial stage of the evolution of the eukaryotic cell, Toni Gabaldón and Alexandros Pitis reconstructed various stages of evolution to get an idea of ​​when they happened.

The two researchers examined in particular the proteins common to all complex organisms and reconstructed their evolution. Using different methods they estimated when those proteins were incorporated into eukaryotic cells. The result is that those connected with the acquisition of mitochondria were acquired latern than those connected to other parts of the cell.

According to this research, cells equipped with  of a certain complexity already existed before the acquisition of mitochondria. Their evolution took place in stages by “waves” of protein arrivals: those related to mitochondria were part of the last wave.

If these results are confirmed, they will constitute a major discovery on the evolution of eukaryotic cells. This will allow to better understand the mechanisms of cell functioning, a crucial step considering the growing importance of biotechnology.