A mitochondrion is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used throughout the cell as a source of chemical energy. They were discovered by Albert von Kölliker in 1857 in the voluntary muscles of insects. The term mitochondrion was coined by Carl Benda in 1898. The mitochondrion is popularly nicknamed the "powerhouse of the cell", a phrase coined by Philip Siekevitz in a 1957 article of the same name.
Symbiogenesis is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria, while chloroplasts are thought to be related to cyanobacteria.
Mitochondrial DNA 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). Mitochondrial DNA is only a small portion of the DNA in a eukaryotic cell; most of the DNA can be found in the cell nucleus and, in plants and algae, also in plastids such as chloroplasts.
In molecular biology, RNA polymerase, or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template.
Excavata is an extensive and diverse but paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.
Human mitochondrial genetics is the study of the genetics of human mitochondrial DNA. The human mitochondrial genome is the entirety of hereditary information contained in human mitochondria. Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the "powerhouses" of the cell.
Transfer-messenger RNA is a bacterial RNA molecule with dual tRNA-like and messenger RNA-like properties. The tmRNA forms a ribonucleoprotein complex (tmRNP) together with Small Protein B (SmpB), Elongation Factor Tu (EF-Tu), and ribosomal protein S1. In trans-translation, tmRNA and its associated proteins bind to bacterial ribosomes which have stalled in the middle of protein biosynthesis, for example when reaching the end of a messenger RNA which has lost its stop codon. The tmRNA is remarkably versatile: it recycles the stalled ribosome, adds a proteolysis-inducing tag to the unfinished polypeptide, and facilitates the degradation of the aberrant messenger RNA. In the majority of bacteria these functions are carried out by standard one-piece tmRNAs. In other bacterial species, a permuted ssrA gene produces a two-piece tmRNA in which two separate RNA chains are joined by base-pairing.
A nuclear gene is a gene that has its DNA nucleotide sequence physically situated within the cell nucleus of a eukaryotic organism. This term is employed to differentiate nuclear genes, which are located in the cell nucleus, from genes that are found in mitochondria or chloroplasts. The vast majority of genes in eukaryotes are nuclear.
Extrachromosomal DNA is any DNA that is found off the chromosomes, either inside or outside the nucleus of a cell. Most DNA in an individual genome is found in chromosomes contained in the nucleus. Multiple forms of extrachromosomal DNA exist, and, while some of these serve important biological functions, they can also play a role in diseases such as cancer.
Guide RNA (gRNA) or single guide RNA (sgRNA) is a short sequence of RNA that functions as a guide for the Cas9-endonuclease or other Cas-proteins that cut the double-stranded DNA and thereby can be used for gene editing. In bacteria and archaea, gRNAs are a part of the CRISPR-Cas system that serves as an adaptive immune defense that protects the organism from viruses. Here the short gRNAs serve as detectors of foreign DNA and direct the Cas-enzymes that degrades the foreign nucleic acid.
The 5S ribosomal RNA is an approximately 120 nucleotide-long ribosomal RNA molecule with a mass of 40 kDa. It is a structural and functional component of the large subunit of the ribosome in all domains of life, with the exception of mitochondrial ribosomes of fungi and animals. The designation 5S refers to the molecule's sedimentation velocity in an ultracentrifuge, which is measured in Svedberg units (S).
DNA-directed RNA polymerase, mitochondrial is an enzyme that in humans is encoded by the POLRMT gene.
Carpediemonas is genus of Metamonada, and belongs to the group Excavata. This organism is a unicellular flagellated eukaryote that was first discovered in substrate samples from the Great Barrier Reef. Carpediemonas can be found in anaerobic intertidal sediment, where it feeds on bacteria. A feature of this species is the presence of a feeding groove, a characteristic of the excavates. Like most other metamonads, Carpediemonas does not rely on an aerobic mitochondrion to produce energy. Instead, it contains hydrogenosomes that are used to produce ATP. This organism has two flagella: a posterior one used for feeding on the substrate, and an anterior one that moves in a slower sweeping motion. Carpediemonas is assigned to the fornicates, where similar Carpediemonas-like organisms are used in researching the evolution within excavates. Although Carpediemonas is a member of the metamonads, it is unusual in the sense that it is free-living and has three basal bodies.
Malawimonas is genus of unicellular, heterotrophic flagellates with uncertain phylogenetic affinities. They have variably being assigned to Excavata and Loukozoa. Recent studies suggest they may be closely related to the Podiata.
Jakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small, and can be found in aerobic and anaerobic environments. The order Jakobida, believed to be monophyletic, consists of only twenty species at present, and was classified as a group in 1993. There is ongoing research into the mitochondrial genomes of jakobids, which are unusually large and bacteria-like, evidence that jakobids may be important to the evolutionary history of eukaryotes.
The mitochondrial ribosome, or mitoribosome, is a protein complex that is active in mitochondria and functions as a riboprotein for translating mitochondrial mRNAs encoded in mtDNA. The mitoribosome is attached to the inner mitochondrial membrane. Mitoribosomes, like cytoplasmic ribosomes, consist of two subunits — large (mt-LSU) and small (mt-SSU). Mitoribosomes consist of several specific proteins and fewer rRNAs. While mitochondrial rRNAs are encoded in the mitochondrial genome, the proteins that make up mitoribosomes are encoded in the nucleus and assembled by cytoplasmic ribosomes before being implanted into the mitochondria.
Monocercomonoides is a genus of flagellate Excavata belonging to the order Oxymonadida. It was established by Bernard V. Travis and was first described as those with "polymastiginid flagellates having three anterior flagella and a trailing one originating at a single basal granule located in front of the anteriorly positioned nucleus, and a more or less well-defined axostyle". It is the first eukaryotic genus to be found to completely lack mitochondria, and all hallmark proteins responsible for mitochondrial function. The genus also lacks any other mitochondria related organelles (MROs) such as hydrogenosomes or mitosomes. Data suggests that the absence of mitochondria is not an ancestral feature, but rather due to secondary loss. Monocercomonoides sp. was found to obtain energy through an enzymatic action of nutrients absorbed from the environment. The genus has replaced the iron-sulfur cluster assembly pathway with a cytosolic sulfur mobilization system, likely acquired by horizontal gene transfer from a eubacterium of a common ancestor of oxymonads. These organisms are significant because they undermine assumptions that eukaryotes must have mitochondria to properly function. The genome of Monocercomonoides exilis has approximately 82 million base pairs, with 18 152 predicted protein-coding genes.
Stygiella /ˌstɪ.d͡ʒiˈɛ.lə/ is a genus of free-living marine flagellates belonging to the family Stygiellidae in the jakobids (excavata).
Cafileria is a genus of marine microscopic protists. It is monotypic, comprising the single species Cafileria marina, described in 2019 from Norway. It is part of a clade of heterotrophic flagellates that consume bacteria, known as Bicosoecida, a basal lineage of Stramenopiles. Due to its small size it is described as a nanoflagellate. It is the only organism where direct connections between mitochondria and the cell nucleus have been observed. Another peculiarity of C. marina is the change in shape of the Golgi apparatus during the cell cycle.
Stygiellidae is a family of free-living marine flagellates belonging to the order Jakobida, a deep-branching lineage within the eukaryotic supergroup Discoba. They are unicellular organisms that commonly inhabit anoxic, sulfide-rich and ammonium-rich marine habitats worldwide.
