Unikont
Encyclopedia
Unikonts are members of the Unikonta, a taxonomic group proposed by Thomas Cavalier-Smith
.
It includes amoebozoa
, opisthokont
s, and Apusozoa
.
cells that, for the most part, have a single emergent flagellum
, or are amoebae with no flagella. The unikonts include opisthokonts (animal
s, fungi
, and related forms) and Amoebozoa
. By contrast other well-known eukaryotic groups, which more often have two emergent flagella (although there are many exceptions) are often referred to as bikonts. Bikonts include Archaeplastida
(plants and relatives), Excavata, Rhizaria
, and Chromalveolata.
in the unikonts but not bacteria or bikonts encode enzymes for synthesis of the pyrimidine
nucleotide
s: carbamoyl phosphate synthase, dihydroorotase
, aspartate carbamoyltransferase
. This must have involved a double fusion, a rare pair of events, supporting the shared ancestry of Opisthokonta and Amoebozoa.
Cavalier-Smith originally proposed that unikonts ancestrally had a single flagellum and single basal body
. This is unlikely, however, as flagellated opisthokonts, as well as some flagellated Amoebozoa, including Breviata, actually have two basal bodies, as in typical 'bikonts' (even though only one is flagellated in most unikonts). This paired arrangement can also be seen in the organization of centrioles in typical animal cells. In spite of the name of the group, the common ancestor of all 'unikonts' was probably a cell with two basal bodies.
Thomas Cavalier-Smith
Professor Thomas Cavalier-Smith , FRS, FRSC, NERC Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford...
.
It includes amoebozoa
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
, opisthokont
Opisthokont
The opisthokonts or "Fungi/Metazoa group" are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the eukaryotic microorganisms that are sometimes grouped in the paraphyletic phylum Choanozoa...
s, and Apusozoa
Apusozoa
The Apusozoa are a phylum comprising several genera of flagellate protozoa. They are usually around 5-20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria...
.
Clade
The group includes eukaryoticEukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
cells that, for the most part, have a single emergent flagellum
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
, or are amoebae with no flagella. The unikonts include opisthokonts (animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
, and related forms) and Amoebozoa
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
. By contrast other well-known eukaryotic groups, which more often have two emergent flagella (although there are many exceptions) are often referred to as bikonts. Bikonts include Archaeplastida
Archaeplastida
The Archaeplastida are a major group of eukaryotes, comprising the red and green algae and the land plants, together with a small group called the glaucophytes. The plastids of all of these organisms are surrounded by two membranes, suggesting they developed directly from endosymbiotic...
(plants and relatives), Excavata, Rhizaria
Rhizaria
The Rhizaria are a species-rich supergroup of unicellular eukaryotes. This supergroup was proposed by Cavalier-Smith in 2002. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods...
, and Chromalveolata.
Characteristics
The unikonts have a triple-gene fusion that is lacking in the bikonts. The three genes that are fused togetherFusion gene
A fusion gene is a hybrid gene formed from two previously separate genes. It can occur as the result of a translocation, interstitial deletion, or chromosomal inversion...
in the unikonts but not bacteria or bikonts encode enzymes for synthesis of the pyrimidine
Pyrimidine
Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...
nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s: carbamoyl phosphate synthase, dihydroorotase
Dihydroorotase
Dihydroorotase is an enzyme which converts Carbamoyl aspartic acid into 4,5-Dihydroorotic acid....
, aspartate carbamoyltransferase
Aspartate carbamoyltransferase
Aspartate carbamoyltransferase catalyzes the first step in the pyrimidine biosynthetic pathway .In E. coli, the enzyme is a multi-subunit protein complex composed of 12 subunits...
. This must have involved a double fusion, a rare pair of events, supporting the shared ancestry of Opisthokonta and Amoebozoa.
Cavalier-Smith originally proposed that unikonts ancestrally had a single flagellum and single basal body
Basal body
A basal body is an organelle formed from a centriole, and a short cylindrical array of microtubules. It is found at the base of a eukaryotic undulipodium and serves as a nucleation site for the growth of the axoneme microtubules...
. This is unlikely, however, as flagellated opisthokonts, as well as some flagellated Amoebozoa, including Breviata, actually have two basal bodies, as in typical 'bikonts' (even though only one is flagellated in most unikonts). This paired arrangement can also be seen in the organization of centrioles in typical animal cells. In spite of the name of the group, the common ancestor of all 'unikonts' was probably a cell with two basal bodies.