theory of endosymiosis

Origin of Eukaryotes

Theory of Endosymbiosis

The evolution of eukaryotes has no fossil record. However, from the study of modern organisms, biologists deduced their theory that eukaryotes evolved from prokaryotes through the endosymbiosis process. The state of one species living inside another species, known as the host, is called endosymbiosis.

Eukaryotes evolved from the Archaea domain of prokaryotes, whereby prokaryotic cell have engulfed aerobic bacteria instead of engulfing other prokaryotes. Membrane infolding is the first process that occurs in the development of eukaryotic cell. Around the nucleus, nuclear envelope is formed due to the inward folding of the plasma membrane. Later, attached to the nuclear envelope, endoplasmic reticulum is produced. The development process of mitochondria and chloroplasts completes the formation of eukaryotic cell.

Some of the researched evidences of biologists on the evolution of eukaryotes from prokaryotes are as follows. (Origin of Eukaryotes. (http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Bacteria/symbiosis.html)

Both use RNA and DNA are the genetic material

Both use the same 20 amino acids

Both have ribosomes and DNA and RNA -- in other words the same cell machinery for protein synthesis.

Both have a lipid bilayer cell membrane.

Both use L. amino acids and D. sugars

The origins of mitochondria and chloroplasts are the main focus of eukaryotes' endosymbiosis. The process of endosymbiosis involves three types of prokaryotic cells: cells that are absorptive and ingestive of inorganic matters, highly oxidized cells that are good for energy process, and photosynthethic cells that develop organic compounds using light energy.

Origin of Mitochondria

During membrane infolding, highly oxidized prokaryotic cells are ingested in eukaryotic cells. These cells are too small and indigestible. Instead of being digested, they continue to live inside the host that becomes an ideal environment for them because of the organic molecules and inorganic compounds the host provides them. The energy released by the endosymbiotic cell (the ingested small prokaryotic cells), on the other hand, provides benefit to the host making it more productive and successful. After some time, the endosymbitic cells lose their cellular autonomy and later become a mitochondrion.