7.8: The Endosymbiotic Theory

It provides some evidence to support the theory that mitochondria and chloroplasts may come from prokaryotes

Life is thought to have appeared on the earth about 4 billion years ago. The internal symbiosis theory thinks that some of the eukaryotic cell organelles were prokaryotic microorganisms. In this theory, the first eukaryotic cell can be an ameboid-like cell containing a nucleus formed by the cytoplasmic membrane sandwiching the chromosome, acquiring nutrients by phagocytosis. Some of these ameboid organisms survive within their organisms after ingesting prokaryotic cells and form symbiotic relationships. Mitochondria are formed when ingesting aerobically respirable bacteria and chloroplasts are formed when photosynthetic bacteria are ingested. As they do not benefit the host cells, they eventually lose the cell wall and most of the DNA. Mitochondria and chloroplasts can not grow outside host cells

Chloroplasts are the same size as prokaryotic cells, divide into two, and have Fts proteins on the cleavage plane like bacteria. Mitochondria are the same size as prokaryotic cells and consist of two divisions.

Mitochondria and chloroplasts have their own ribosomes and have 30 S and 50 S subunits instead of 40 S and 60 S.

Primitive eukaryotic microorganisms such as Giardia and Trichomonas have nuclear membranes, but do not have mitochondria

Evidence is not so persuasive, but flagellum and cilia may also come from Spirohetera.

Figure \ (\ PageIndex {1} \): Model of mitochondrial and plastid origin. This model has aerobic bacteria and then mitochondrial eukaryotes swallowing cyanobacteria. Image licensed by Kelvinsong

We provide three pieces of evidence to support the theory that mitochondria and chloroplasts may come from prokaryotes

Internal symbiotic theory that several organelles in eukaryotic cells were once prokaryotic microorganisms

Mitochondria and chloroplasts have their own ribosomes and have 30 S and 50 S subunits instead of 40 S and 60 S.

Internal symbiotic theory suggests that mitochondria and chloroplast in today's eukaryotic cells were once independent prokaryotic microorganisms

For over 100 years, the theory of symbiosis symbiosis has considered the difference between prokaryotic cells and eukaryotic cells. In order to explain the origin of eukaryotes and their mitochondria, more than 20 different versions of internal symbiosis theory are proposed in the literature. There are few models that can explain eucaryotic anaerobic bacteria. The role of energy and the energy limitation of prokaryotic tissue for evolutionary innovation in cellular history have recently influenced the theory of internal symbiosis. Only cells with mitochondria have bioenergetic means to obtain the complexity of eukaryotic cells, which is why there is no true intermediate in the transition from prokaryotes to eukaryotes. In the current internal symbiosis theory, it is thought that the host is not an eukaryote but an archaebacter (archaea). Therefore, the history and biology of the archaeal evolution have increased dependence on eukaryotes more than ever.

The theory of symbiosis symbiosis is a unified widely accepted theory about how organelles are produced in living organisms different from eukaryotes. In the theory of internal symbiosis, consistent with the general theory of evolution, all creatures come from a common ancestor. Such ancestry may be similar to bacteria or prokaryotes in which single-stranded DNA is surrounded by the plasma membrane. Over time, the morphology and function of these bacteria have differentiated. Some bacteria acquire the ability to process energy from the environment in a novel way. Photosynthetic bacteria have developed a route to produce sugar from sunlight. Other organisms developed a new way to use this sugar, which is oxidative phosphorylation. And it produces ATP and oxygen from glycolysis. You can then use ATP to supply energy to other reactions within the cell.