The kinetoplastids are a group of single-cell flagellate protozoa, including a number of parasites responsible for serious diseases in humans and other animals, as well as various forms found in soil and aquatic environments. They are members of the phylum Euglenozoa and their major distinguishing feature is the presence of a kinetoplast, a DNA-containing granule located within the single mitochondrion associated with the base of the cell's flagella (the basal body).
The kinetoplastids were first defined by Honigberg in 1961 as the flagellate order Kinetoplastida. They are traditionally divided into the biflagellate Bodonidae and uniflagellate Trypanosomatidae; the former appears to be paraphyletic to the latter. One family of kinetoplastids, the trypanosomatids, is notable as it includes several genera which are exclusively parasitic. Bodo is a typical genus within kinetoplastida and including various common free-living species which feed on bacteria. Others include Cryptobia and the parasitic Leishmania.
Kinetoplastids are eukaryotic and possess normal eukaryotic organelles, for example the nucleus, mitochondrion, golgi apparatus and flagellum. Along with these universal structures kinetoplastids have several distinguishing morphological features such as the kinetoplast, sub-pellicular microtubule array and the paraflagellar rod.
The kinetoplast, after which the class is named, contains the mitochondrial genome and is a dense DNA containing granule within the cell's single mitochondrion. The structure is made up of a network of concatenated circular DNA molecules and their associated structural proteins along with DNA and RNA polymerases. The kinetoplast is found at the base of a cell's flagella and is associated to the flagellum basal body by a cytoskeletal structure.
The cytoskeleton of kinetoplastids is primarily made up of microtubules. These make a highly regular array, the sub-pellicular array, which run parallel just under the cell surface along the long axis of the cell. Other microtubules with more specialised roles, such as the rootlet microtubules, are also present. Kinetoplastids are capable of forming actin microfilaments but their role in the cytoskeleton is not clear. Other cytoskeletal structures include the specialised attachment between the flagellum and the kinetoplast.
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