It is claimed that say that during evolution the Microorganisms fused with our cells and became an integral part of our cellular machinery. Today we are going to talk about a theory that holds these claims. The theory of Symbiogenesis, or endosymbiotic theory. Thank you and Namaste.
All animals and plants are made up of eukaryotic cells. These cells are the basic unit of structure and function of any living entity.
These cells have specialized cell organelles that perform various functions. Like mitochondria; which is called the powerhouse of the cell because it generates energy, the endoplasmic reticulum is protein synthesis machinery of the cell, Golgi bodies are the transportation system and nucleus is the brain of the cell.
Researchers believe that these organelles are originated because the prokaryotic cells fused with eukaryotic cells and became an integral part of the eukaryotic cell. There are interesting proofs that were provided in support of this hypothesis. We are going to discuss those evidence in detail so stay tuned to understand the theory of Symbiogenesis.
It is an evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. It was given by the Russian botanist Konstantin Mereschkowski, in between1905 and 1910. Additionally, the microbiological evidence for this theory was provided by Lynn Margulis in 1967.
It holds that the organelles distinguishing eukaryotic cells evolved through the symbiosis of individual single-celled prokaryotes (bacteria and archaea).
The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells represent formerly free-living prokaryotes taken one inside the other in endosymbiosis.
Some mitochondria and plastids contain single circular DNA molecules similar to the chromosomes of bacteria.
New mitochondria and plastids are formed only through binary fission, the form of cell division used by bacteria and archaea.
If a cell's mitochondria or chloroplasts are removed, the cell does not have the means to create new ones. For example, in some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate.
Transport proteins called porins are found in the outer membranes of mitochondria and chloroplasts and are also found in bacterial cell membranes.
A membrane lipid called cardiolipin is exclusively found in the inner mitochondrial membrane and bacterial cell membranes.
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Genome comparisons suggest a close relationship between mitochondria and Rickettsial bacteria. Genome comparisons also suggest a close relationship between plastids and cyanobacteria.
Many genes in the genomes of mitochondria and chloroplasts have been lost or transferred to the nucleus of the host cell. Consequently, the chromosomes of many eukaryotes contain genes that originated from the genomes of mitochondria and plastids.
Mitochondrial and plastid ribosomes are more similar to those of bacteria (70S) than those of eukaryotes ribosome. Proteins created by mitochondria and chloroplasts use N-formylmethionine as the initiating amino acid, as do proteins created by bacteria but not proteins created by eukaryotic nuclear genes.
These were the key evidences proposed in favour of theory of Symbiogenesis. All these evidences support that the eukaryotic cells were created by fusion of bacterial cells and live inside the eukaryotic cells in a symbiotic relationship.
