How prokaryotes led to eukaryotes

Subject: Science and technology

Section: Biotechnology

Classification of organisms:

Organisms on planet Earth are broadly divided into prokaryotes and eukaryotes.
- Prokaryotes are unicellular, do not have any organelles such as mitochondria, and their DNA is not packaged into a nucleus.
- Eukaryotes have mitochondria, their DNA is packaged into a nucleus, and most eukaryotes are complex, multicellular beings.

Archaea:

But a subset of unicellular organisms known as Archaea have a different line of descent as compared to bacteria.
The two differ in the composition of their cell walls and in the sequence of some of their genes.
The term Archaea, suggesting ancient, was used because the first members of this domain were found living in extreme environments of very high temperatures or very high salt.
One group of archaea were shown to have proteins that closely resembled eukaryotic proteins (multicellular organism).
These organisms are found in a geological formation where geothermally heated water is forced out of a ridge in the Atlantic Ocean floor at a depth of 2400 meters below sea level.
Many other related members were later found in unusual ecosystems and came to be collectively called the Asgard, which is the home of the Gods in Norse mythology.

Mitochondria as endosymbionts:

The mitochondria in eukaryotic cells and photosynthesizing chloroplasts in plant cells have evolved from free-living bacteria.
The ancestor of mitochondria was a proteobacterium that was engulfed by an Asgard archaean organism.
Descendants of this endosymbiotic union gave rise to animals, fungi and plants.
In plants, the Asgard-mitochondrial union was followed by the intake of a photosynthesizing cyanobacterium, which became the chloroplast.

Plants do it differently:

Researchers have found that plants adopt different strategies from animals and fungi.
Proteins are made up of amino acids. Nature uses only left-handed amino acids; the right-handed ones can be poisonous.
The mechanism for discriminating ‘good’ from ‘bad’ is different for Asgards and bacteria.
The paper shows that animals and fungi work their way around this discrepancy by forcing the mitochondria to change.
Plants segregate the two policing machineries in the cytoplasm and in mitochondria.