Endosymbiosis during Biological Evolution
# Living one or more prokaryotes in another prokaryote with the symbiotic mode of life led to the Origin of Eukaryotes.
Origin of Eukaryotes (1.6 to 2.7 billion years ago): (Endosymbiosis)
Introduction:
Endosymbiosis is a biological process that involves one organism living inside another organism, a widely accepted scientific explanation for the origin of eukaryotic cells and their membrane-bound organelles. It has played a significant role in the evolution of eukaryotic life on Earth by the addition of some more important cellular organelles such as mitochondria and chloroplasts etc. This theory suggests that primitive eukaryotic cells engulfed a free-living prokaryotic cell, such as a bacterium, but instead of digesting it, the host cell formed a symbiotic relationship with the engulfed cell. The small organisms engulfed in the cell get protection and nutrition. The eukaryotic cell is enriched with the different organelles for more effective metabolic activities, and a fine symbiotic relationship is established. Eukaryotic cells became the building blocks for the evolution of complex organisms like plants, animals, and fungi.
The step-by-step process took place in the Origin of Evolution of Eukaryotes:
- Initial Engulfment: The process likely began with the engulfment of a small aerobic prokaryotic cell, resembling modern-day bacteria, by a larger anaerobic prokaryotic host cell. This event is thought to have occurred around 1.6 to 2.7 billion years ago.
- Symbiotic Relationship: Instead of being digested or destroyed by the host cell, the engulfed cell and the host cell entered into a mutually beneficial relationship. The engulfed cell was protected within the host cell, while the host cell gained access to the energy produced by the engulfed cell.
- Evolutionary Changes: Over time, the engulfed cell began to undergo changes. These changes likely included a reduction in its genome, as many of its genes became redundant or unnecessary due to the host cell providing essential resources. The host cell also provided protection from external threats.
- Development of Organelles: Eventually, the engulfed cell evolved into an organelle. Mitochondria, for example, are believed to have evolved from an engulfed aerobic bacterium, while chloroplasts are thought to have originated from an engulfed photosynthetic bacterium. These organelles retained some of their own genetic material (DNA), which is why they still have their own genomes separate from the host cell’s nuclear DNA.
- Mutualistic Relationship: The host cell and the newly formed organelles developed a highly efficient and mutually beneficial relationship. Mitochondria, for instance, became responsible for producing energy (in the form of ATP) through oxidative phosphorylation. Chloroplasts became responsible for photosynthesis, converting sunlight into energy and producing sugars.
- Eukaryotic Cell Formation: With the acquisition of these organelles, the host cell became more energetically efficient and adaptable, which likely contributed to its survival and replication advantage. Over time, this symbiotic relationship between the host cell and its organelles became stable, and eukaryotic cells with a nucleus and membrane-bound organelles emerged.
Final words:
The endosymbiotic theory is supported by several lines of evidence, including the similarities between the DNA of mitochondria and chloroplasts and that of free-living bacteria, as well as similarities in their ribosomes and membranes. Additionally, some protists, such as modern-day amoebas, have structures resembling intermediate stages of this process, providing further support for the theory. This theory has been instrumental in our understanding of the evolution of complex life forms and the development of eukaryotic cells with their intricate internal structures.