A report on Mitochondrion and Symbiogenesis

Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy
Internal symbiont: mitochondrion has a matrix and membranes, like a free-living alphaproteobacterial cell, from which it may derive.
Simplified structure of a mitochondrion.
Konstantin Mereschkowski's 1905 tree-of-life diagram, showing the origin of complex life-forms by two episodes of symbiogenesis, the incorporation of symbiotic bacteria to form successively nuclei and chloroplasts.
Cross-sectional image of cristae in a rat liver mitochondrion to demonstrate the likely 3D structure and relationship to the inner membrane
One model for the origin of mitochondria and plastids
Electron transport chain in the mitochondrial intermembrane space
Modern endosymbiotic theory posits that simple life forms merged, forming cell organelles, like mitochondria.
Transmission electron micrograph of a chondrocyte, stained for calcium, showing its nucleus (N) and mitochondria (M).
Kwang Jeon's experiment: [I] Amoebae infected by x-bacteria [II] Many amoebae become sick and die [III] Survivors have x-bacteria living in their cytoplasm [IV] Antibiotics kill x-bacteria: host amoebae die as now dependent on x-bacteria.
Typical mitochondrial network (green) in two human cells (HeLa cells)
Mitochondria of a mammal lung cell visualized using Transmission Electron Microscopy
Model of the yeast multimeric tethering complex, ERMES
Diagram of endomembrane system in eukaryotic cell
Evolution of MROs
The human mitochondrial genome has retained genes encoding 2 rRNAs, 22 tRNAs, and 13 redox proteins.
The circular 16,569 bp human mitochondrial genome encoding 37 genes, i.e., 28 on the H-strand and 9 on the L-strand.
Simplified chart showing the three main mergers of the endosymbiotic theory
The three main mergers of the endosymbiotic theory
An anaerobic eukaryote with no mitochondria, perhaps resembling the present-day Giardia duodenalis parasite (which has secondarily lost its mitochondria), could have engulfed an aerobic proteobacterium and become symbiotic with it, and aerobic.

The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes (more closely related to the Bacteria than to the Archaea) taken one inside the other in endosymbiosis.

- Symbiogenesis

There are two hypotheses about the origin of mitochondria: endosymbiotic and autogenous.

- Mitochondrion
Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy

11 related topics with Alpha

Overall

Eukaryote

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Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope.

The endomembrane system and its components
Simplified structure of a mitochondrion
Longitudinal section through the flagellum of Chlamydomonas reinhardtii
Structure of a typical animal cell
Structure of a typical plant cell
Fungal Hyphae cells: 1 – hyphal wall, 2 – septum, 3 – mitochondrion, 4 – vacuole, 5 – ergosterol crystal, 6 – ribosome, 7 – nucleus, 8 – endoplasmic reticulum, 9 – lipid body, 10 – plasma membrane, 11 – spitzenkörper, 12 – Golgi apparatus
This diagram illustrates the twofold cost of sex. If each individual were to contribute the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.
Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes and prokaryotes
One hypothesis of eukaryotic relationships – the Opisthokonta group includes both animals (Metazoa) and fungi, plants (Plantae) are placed in Archaeplastida.
A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups
The three-domains tree and the Eocyte hypothesis
Phylogenetic tree showing a possible relationship between the eukaryotes and other forms of life; eukaryotes are colored red, archaea green and bacteria blue
Eocyte tree.
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.

Eukaryotic cells typically contain other membrane-bound organelles such as mitochondria and Golgi apparatus; and chloroplasts can be found in plants and algae.

Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion.

Bacteria

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Bacteria (singular bacterium, common noun bacteria) are ubiquitous, mostly free-living organisms often consisting of one biological cell.

Bacteria (singular bacterium, common noun bacteria) are ubiquitous, mostly free-living organisms often consisting of one biological cell.

Rod-shaped Bacillus subtilis
Phylogenetic tree of Bacteria, Archaea and Eucarya. The vertical line at bottom represents the last universal common ancestor.
Bacteria display many cell morphologies and arrangements
The range of sizes shown by prokaryotes (Bacteria), relative to those of other organisms and biomolecules.
Structure and contents of a typical Gram-positive bacterial cell (seen by the fact that only one cell membrane is present).
An electron micrograph of Halothiobacillus neapolitanus cells with carboxysomes inside, with arrows highlighting visible carboxysomes. Scale bars indicate 100 nm.
Helicobacter pylori electron micrograph, showing multiple flagella on the cell surface
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
Many bacteria reproduce through binary fission, which is compared to mitosis and meiosis in this image.
A culture of ''Salmonella
A colony of Escherichia coli
Helium ion microscopy image showing T4 phage infecting E. coli. Some of the attached phage have contracted tails indicating that they have injected their DNA into the host. The bacterial cells are ~ 0.5 µm wide.
Transmission electron micrograph of Desulfovibrio vulgaris showing a single flagellum at one end of the cell. Scale bar is 0.5 micrometers long.
The different arrangements of bacterial flagella: A-Monotrichous; B-Lophotrichous; C-Amphitrichous; D-Peritrichous
Streptococcus mutans visualised with a Gram stain.
Phylogenetic tree showing the diversity of bacteria, compared to other organisms. Here bacteria are represented by three main supergroups: the CPR ultramicrobacterias, Terrabacteria and Gracilicutes according to recent genomic analyzes (2019).
Overview of bacterial infections and main species involved.
Colour-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells
In bacterial vaginosis, beneficial bacteria in the vagina (top) are displaced by pathogens (bottom). Gram stain.
Antonie van Leeuwenhoek, the first microbiologist and the first person to observe bacteria using a microscope.

This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya (sometimes in highly reduced form, e.g. in ancient "amitochondrial" protozoa).

This is known as primary endosymbiosis.

A representation of the endosymbiotic theory

Endosymbiont

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Any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.

Any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.

A representation of the endosymbiotic theory
An overview of the endosymbiosis theory of eukaryote origin (symbiogenesis).
Diagram of cospeciation, where parasites or endosymbionts speciate or branch alongside their hosts. This process is more common in hosts with primary endosymbionts.
Pea aphids are commonly infested by parasitic wasps. Their secondary endosymbionts attack the infesting parasitoid wasp larvae promoting the survival of both the aphid host and its endosymbionts.

When a symbiont reaches this stage, it begins to resemble a cellular organelle, similar to mitochondria or chloroplasts.

This process is commonly referred to as symbiogenesis.

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.

Organelle

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Organelle is a specialized subunit, usually within a cell, that has a specific function.

Organelle is a specialized subunit, usually within a cell, that has a specific function.

(A) Electron micrograph of Halothiobacillus neapolitanus cells, arrows highlight carboxysomes. (B) Image of intact carboxysomes isolated from H. neapolitanus. Scale bars are 100 nm.
Structure of Candidatus Brocadia anammoxidans, showing an anammoxosome and intracytoplasmic membrane

They include structures that make up the endomembrane system (such as the nuclear envelope, endoplasmic reticulum, and Golgi apparatus), and other structures such as mitochondria and plastids.

According to the endosymbiotic theory, they are believed to have originated from incompletely consumed or invading prokaryotic organisms.

Diagram of a typical prokaryotic cell

Prokaryote

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Single-celled organism that lacks a nucleus, and other membrane-bound organelles.

Single-celled organism that lacks a nucleus, and other membrane-bound organelles.

Diagram of a typical prokaryotic cell
Phylogenetic ring showing the diversity of prokaryotes, and symbiogenetic origins of eukaryotes
Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes
Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view, one of many on the relative positions of Prokaryotes and Eukaryotes, implies that the universal common ancestor was relatively large and complex.
Comparison of eukaryotes vs. prokaryotes
Phylogenetic tree showing the diversity of prokaryotes. 
This 2018 proposal shows eukaryotes emerging from the archaean Asgard group which represents a modern version of the eocyte hypothesis. Unlike earlier assumptions, the division between bacteria and the rest is the most important difference between organisms.

Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell.

Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors.

Figure 1: Ribosomes assemble polymeric protein molecules whose sequence is controlled by the sequence of messenger RNA molecules. This is required by all living cells and associated viruses.

Ribosome

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Ribosomes, also called Palade granules (after discoverer George Palade and due to their granular structure), are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation).

Ribosomes, also called Palade granules (after discoverer George Palade and due to their granular structure), are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation).

Figure 1: Ribosomes assemble polymeric protein molecules whose sequence is controlled by the sequence of messenger RNA molecules. This is required by all living cells and associated viruses.
Ribosome rRNA composition for prokaryotic and eukaryotic rRNA
Figure 2: Large (red) and small (blue) subunit fit together.
Figure 3: Molecular structure of the 30S subunit from Thermus thermophilus. Proteins are shown in blue and the single RNA chain in brown.
Figure 4: Atomic structure of the 50S subunit from Haloarcula marismortui. Proteins are shown in blue and the two RNA chains in brown and yellow. The small patch of green in the center of the subunit is the active site.
Figure 5: Translation of mRNA (1) by a ribosome (2)(shown as small and large subunits) into a polypeptide chain (3). The ribosome begins at the start codon of RNA ( AUG ) and ends at the stop codon ( UAG ).
Figure 6: A ribosome translating a protein that is secreted into the endoplasmic reticulum.

In eukaryotes, ribosomes are present in mitochondria (sometimes called mitoribosomes) and in plastids such as chloroplasts (also called plastoribosomes).

These ribosomes are similar to those of bacteria and these organelles are thought to have originated as symbiotic bacteria Of the two, chloroplastic ribosomes are closer to bacterial ones than mitochrondrial ones are.

Alphaproteobacteria

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Class of bacteria in the phylum Pseudomonadota .

Class of bacteria in the phylum Pseudomonadota .

Moreover, the class is sister to the protomitochondrion, the bacterium that was engulfed by the eukaryotic ancestor and gave rise to the mitochondria, which are organelles in eukaryotic cells (See endosymbiotic theory).

Proto-mitochondrion

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The proto-mitochondrion is the hypothetical ancestral bacterial endosymbiont from which all mitochondria in eukaryotes are thought to descend, after an episode of symbiogenesis which created the aerobic eukaryotes.

Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles, found in all eukaryotic cells, are the powerhouse of the cell. The mitochondria, and thus mitochondrial DNA, are passed exclusively from mother to offspring through the egg cell.

Mitochondrial DNA

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Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles, found in all eukaryotic cells, are the powerhouse of the cell. The mitochondria, and thus mitochondrial DNA, are passed exclusively from mother to offspring through the egg cell.
Electron microscopy reveals mitochondrial DNA in discrete foci. Bars: 200 nm. (A) Cytoplasmic section after immunogold labelling with anti-DNA; gold particles marking mtDNA are found near the mitochondrial membrane (black dots in upper right). (B) Whole mount view of cytoplasm after extraction with CSK buffer and immunogold labelling with anti-DNA; mtDNA (marked by gold particles) resists extraction. From Iborra et al., 2004.
Human mitochondrial DNA with the 37 genes on their respective H- and L-strands.
Human mitochondrial DNA with groups of protein-, rRNA- and tRNA-encoding genes.
The involvement of mitochondrial DNA in several human diseases.
Animal species mtDNA base composition was retrieved from the MitoAge database and compared to their maximum life span from AnAge database.

Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP).

This theory is called the endosymbiotic theory.

Margulis in 2005

Lynn Margulis

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Margulis in 2005
The chloroplasts of glaucophytes like this Glaucocystis have a peptidoglycan layer, evidence of their endosymbiotic origin from cyanobacteria.

Lynn Margulis (born Lynn Petra Alexander; March 5, 1938 – November 22, 2011) was an American evolutionary biologist, and was the primary modern proponent for the significance of symbiosis in evolution.

Still a junior faculty member at Boston University at the time, her theory that cell organelles such as mitochondria and chloroplasts were once independent bacteria was largely ignored for another decade, becoming widely accepted only after it was powerfully substantiated through genetic evidence.