What is the endosymbiosis theory

Endosymbiotic Theory

1 definition

The Endosymbiotic Theory states that in the course of evolution eukaryotes emerged from the symbiosis of prokaryotes and thus higher living beings could develop. The theory is now widely accepted.

2 theory

Intracellular cell organelles enclosed by a membrane are characteristic of eukaryotic cells.

This development into eukaryotic cells probably took place in two broad steps:

It is assumed that an archaeon as a primordial bacterium initially entered into a symbiosis with an α-proteobacterium. This was followed by the uptake of a cyanobacterium.

2.1 Intussusception of the plasma membrane

According to this theory, the organelles of a eukaryote, which have a single membrane, were created by absorbing their own plasma membrane. This process is called intussusception. This is how organelles such as the endoplasmic reticulum, the Golgi apparatus or the nuclear envelope came about.

2.2 Endosymbiosis

With the uptake of proteobacteria and cyanobacteria via a kind of phagocytosis, mitochondria and plastids such as chloroplasts could arise.

3 indications for the endosymbiotic theory

Various properties of eukaryotic cells are now considered to be indicative of the endosymbiotic theory:

  • The own DNA of mitochondria (mtDNA) and chloroplasts are similar in their ring structure. They also contain both histones and have homologies to bacterial DNA.
  • The ribosomes of the mitochondria and the chloroplasts have similarities to the ribosomes of bacteria (size, composition).
  • It is known that the protein biosynthesis of bacteria can be inhibited by antibiotics; some of these active ingredients also influence the biosynthesis of mitochondrial and plastid proteins.
  • The double membrane of the organelles is further evidence for this theory. The inner membrane is probably the original membrane of the immigrated bacterium and the outer membrane comes from the original bacterium.
  • The cell division of the mitochondria and chloroplasts also takes place before the actual cell division of the cell, so it is autonomous.
  • Intermediate stages of endosymbiosis can still be seen today in different living beings (examples: corals, mussels, dinoflagellates)

4 sources