Mitochondria plays an essential role in producing metabolic energy in eukaryotic cells. They are responsible for most of the useful energy derived from the breakdown of carbohydrates and fatty acids, which is converted to Adenosine Triphosphate(ATP – called the currency of energy). This is the reason why mitochondria is known as the “Powerhouse of the cell”. The function of mitochondria is oxidative metabolism, which involves the oxidative breakdown of glucose and fatty acid which further becomes the principle of metabolic energy source in an animal cell.
Mitochondria evolves from eubacteria, living in larger cells. The variable feature of mitochondria is, they contain their own DNA, which encodes some of their components themselves without the help of nuclear genomes. The mitochondrial DNAs are replicated each time and the organelle divides by fusion and fission as in Fig.1 ( likewise the binary fission in bacteria).
The genes they encode transcribe within the organelle and ribosomes surrounds mitochondria in the form of clusters. Mitochondria, thus contain their own genetic systems, which are different from the nuclear genome of the cell. Furthermore, the ribosome and ribosomal RNAs of these organelles are more closely related to those of bacteria than those encoded by the nuclear genomes of eukaryotes. Mitochondrial genomes are usually circular DNA molecules like those of bacteria, which are present in multiple copies per organelle.
THE HISTORY OF MITOCHONDRIAL EVOLUTION
Mitochondria, an aerobic bacteria( prokaryote) is swallowed by the eukaryotic cell(host cell). Thereby it evolves making an endosymbiotic relationship and during that evolution they occupy the role of an organelle. The genetic function of mitochondrial DNA (mtDNA) was first fully revealed by complete sequencing of the ∼16kb(KiloBasepairs) mitochondrial genome from several mammalian species. This became a storm breaking milestone which paved the way to progress on the evolution theory.
Lynn Margulis published Origin of Eukaryotic Cells in 1970, an influential book that effectively revived the fact that mitochondria was evolved from free-living bacteria by the endosymbiotic relationship within an eukaryotic host cell. Regardless of several debates on evolution theories, technological developments in DNA cloning and sequencing in the 1970s and 1980s opened the way to the detailed characterization of mitochondrial genomes and genes, and the generation of molecular data confirming bacterial origin of the mitochondrial genome. This allowed researchers to pinpoint the bacterial phyla to which these organelles are most closely related.
The record of mitochondrial proteomics(study of mitochondrial proteins) shows the mosaic evolutionary origin of protein complement that was derived from a class of bacteria (α-Proteobacterial origin). Mitochondrial-specific proteins which emerge within the eukaryotic lineage pointing to the α-Proteobacterial endosymbiosis were identified.
Mitochondria and Chloroplast
The above-given features belonging to mitochondria have always been accompanied by the characteristics of the chloroplast. Both Mitochondria and Chloroplast are from the bacterial origin and both had been evolved by the same Endosymbiotic relationship. They differ only on the place they can be found(Mitochondria in animal cell and Chloroplast in Plant cell). Otherwise both are powerhouses for their respective cells, atleast by their function.
In a similar way, certain present-day marine protists engulf algae so that those algae would carry out photosynthesis for this host, thus serving as an endosymbiant.
“It is not the strongest of the species that survives, not the most intelligent that survives. It is the one that is the most adaptable to change.”
– Charles Darwin, The Origin of Species
References:
1.The cell- A Molecular Approach – GEOFFREY M.COOPER, ROBERT E.HAUSMAN
2. Cell And Molecular Biology Concepts And Experiments, GERALD KARP
3. Mitochondrial Evolution , Michael W. Gray
READ MORE: “Endomterial cancer – Early detection“
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