Mitochondria life story
- Heba Salah
- Mar 10
- 2 min read
Updated: Apr 1
Mitochondria are called the powerhouse of the cell because they are the main site of ATP synthesis in aerobic cells. that's because Krebs cycle mainly takes place in the mitochondrial matrix.
One of the things that is special about mitochondria is the "mitochondrial DNA" which is responsible of coding some of subunits of complexes that are responsible of ATP synthesis, it is also responsible of coding mRNA and rRNA of mitochondria.
The point is that mitochondrial DNA differs from nuclear DNA but it is similar to bacterial DNA instead.
The similarity between mitochondria and bacteria
similarity in structure
as we know, mitochondria has two membranes (the outer mitochondrial membrane and the inner mitochondrial membrane), inter-membranous space, and a matrix. the same structure was observed in Cram +ve bacteria such as Rickettsia.
the mitochondrial ATP synthesis is similar to the bacterial aerobic ATP synthesis, although it is more simple in case of bacteria.
they both have a circular DNA.
similarity in DNA
over the years, many common features have been discovered between mitochondrial and prokaryote DNA. For example, E-coli DNA (which considered the most popular model for the molecular study) has a double-stranded, circular DNA.
those similarities -alongside many others wasn't mentioned- to what is called "Endosymbiotic theory of mitochondria".
The Endosymbiotic theory of mitochondria
the theory says that the mitochondria once was a free living prokaryotes and then it became organelle in eukaryotic cell. the theory is based mainly on physiological and biochemical similarity of mitochondria to prokaryotes.
when and how did that happen?
that happened 1.5 billion years ago, maybe because increasing of O2 levels in the atmosphere. it is believed that ancient "α-proteobacteria" related to "Rickettsiales" became an endosymbiotic organism and became part of the host (probably Asgard superphylum archaea).
over the years, mitochondria went through many evolutionary stages and wholly transformed from a free living bacteria to a cell organelle.
This figure shows mitochondrial origin in a prokaryotic host. (a–h) Illustrations for various stages depicting the transition of a H2-dependent archaeal host (in red) and a facultatively anaerobic α-proteobacterium (in blue) to an eukaryote.
The evolutionary process that led to formation of mitochondria is considered "irreversible" as the two independent organisms become a single individual.
Ageing of mitochondria
Mitochondria have shown that it has great importance in "longevity" and "ageing", the theory says that the free radicals produced through life as a result of aerobic respiration lead to cumulative damage to DNA, lipids, and proteins, which lead finally to death of the mitochondria.
the decrease in energy production that caused by decreasing the functional mitochondrial number finally lead to cell death.
References
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