=== Tetrahymena&nbsp; === As a ciliated&nbsp;[https://en.wikipedia.org/wiki/Protozoan protozoan],&nbsp;'''''Tetrahymena thermophila'''''&nbsp;exhibits&nbsp;[https://en.wikipedia.org/wiki/Nuclear_dimorphism nuclear dimorphism]: two types of cell&nbsp;[https://en.wikipedia.org/wiki/Cell_nucleus nuclei]. They have a bigger,&nbsp;[https://en.wikipedia.org/wiki/Somatic_cell non-germline]&nbsp;[https://en.wikipedia.org/wiki/Macronucleus macronucleus]&nbsp;and a small,&nbsp;[https://en.wikipedia.org/wiki/Germline germline]&nbsp;[https://en.wikipedia.org/wiki/Micronucleus micronucleus]&nbsp;in each cell at the same time and these two carry out different functions with distinct cytological and biological properties. This unique versatility allows scientists to use&nbsp;''Tetrahymena''&nbsp;to identify several key factors regarding&nbsp;[https://en.wikipedia.org/wiki/Gene_expression gene expression]&nbsp;and genome integrity. In addition,&nbsp;''Tetrahymena''&nbsp;possess hundreds of&nbsp;[https://en.wikipedia.org/wiki/Cilia cilia]&nbsp;and has complicated&nbsp;[https://en.wikipedia.org/wiki/Microtubule microtubule]&nbsp;structures, making it an optimal model to illustrate the diversity and functions of microtubule arrays. Because&nbsp;''Tetrahymena''&nbsp;can be grown in a large quantity in the laboratory with ease, it has been a great source for biochemical analysis for years, specifically for&nbsp;[https://en.wikipedia.org/wiki/Enzyme enzymatic]&nbsp;activities and purification of&nbsp;[https://en.wikipedia.org/wiki/Cell_(biology)#Subcellular_components sub-cellular components]. In addition, with the advancement of genetic techniques it has become an excellent model to study the gene function&nbsp;''in vivo''. The recent sequencing of the macronucleus genome should ensure that&nbsp;''Tetrahymena''&nbsp;will be continuously used as a model system. ''Tetrahymena thermophila''&nbsp;exists in 7 different sexes ([https://en.wikipedia.org/wiki/Mating_type mating types]) that can reproduce in 21 different combinations, and a single tetrahymena cannot reproduce sexually with itself. Each organism "decides" which sex it will become during mating, through a&nbsp;[https://en.wikipedia.org/wiki/Stochastic stochastic]&nbsp;process.<sup id="cite_ref-PLOS2013_5-0">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-PLOS2013-5 [5]]</sup><sup id="cite_ref-6">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-6 [6]]</sup> Studies on&nbsp;''Tetrahymena''&nbsp;have contributed to several scientific milestones including: #First cell which showed synchronized division, which led to the first insights into the existence of mechanisms which control the&nbsp;[https://en.wikipedia.org/wiki/Cell_cycle cell cycle].<sup id= "cite_ref-whitepaper_7-0">[https://en.wikipedia.org/wiki/Tetrahymena #cite_note-whitepaper-7 [7]]</sup> #Identification and purification of the first&nbsp;[https://en.wikipedia.org/wiki/Cytoskeleton cytoskeleton]&nbsp;based&nbsp;[https://en.wikipedia.org/wiki/Motor_protein motor protein]&nbsp;such as&nbsp;''[https://en.wikipedia.org/wiki/Dynein dynein]''.<sup id="cite_ref-whitepaper_7-1">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup> #Aid in the discovery of&nbsp;''[https://en.wikipedia.org/wiki/Lysosomes lysosomes]''&nbsp;and&nbsp;''[https://en.wikipedia.org/wiki/Peroxisomes peroxisomes]''.<sup id="cite_ref-whitepaper_7-2">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup> #Early molecular identification of somatic genome rearrangement.<sup id="cite_ref-whitepaper_7-3">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup> #Discovery of the molecular structure of&nbsp;''[https://en.wikipedia.org/wiki/Telomeres telomeres]'',&nbsp; ''[https://en.wikipedia.org/wiki/Telomerase telomerase]''&nbsp;enzyme, the templating role of telomerase RNA and their roles in cellular senescence and chromosome healing (for which a Nobel Prize was won).<sup id="cite_ref-whitepaper_7-4">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup> #Nobel Prize–winning co-discovery (1989, in Chemistry) of catalytic&nbsp;[https://en.wikipedia.org/wiki/RNA RNA]&nbsp;(''[https://en.wikipedia.org/wiki/Ribozymes ribozyme]'').<sup id="cite_ref-whitepaper_7-5">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup><sup id="cite_ref-8">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-8 [8]]</sup> #Discovery of the function of&nbsp;[https://en.wikipedia.org/wiki/Histone histone]&nbsp;[https://en.wikipedia.org/wiki/Acetylation acetylation].<sup id="cite_ref-whitepaper_7-6">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-whitepaper-7 [7]]</sup> #Demonstration of the roles of&nbsp;[https://en.wikipedia.org/wiki/Posttranslational_modification posttranslational modification]&nbsp;such as acetylation and glycylation on&nbsp;[https://en.wikipedia.org/wiki/Tubulins tubulins]&nbsp;and discovery of the enzymes responsible for some of these modifications (glutamylation) #Crystal structure of 40S ribosome in complex with its initiation factor eIF1 #First demonstration that two of the "universal"&nbsp;[https://en.wikipedia.org/wiki/Stop_codon stop codons], UAA and UAG, will code for the amino acid&nbsp;[https://en.wikipedia.org/wiki/Glutamine glutamine]&nbsp;in some eukaryotes, leaving UGA as the only termination codon in these organisms.<sup id="cite_ref-9">[https://en.wikipedia.org/wiki/Tetrahymena#cite_note-9 [9]]</sup>  <span style="font-size: 13.3333px;">link&nbsp;:&nbsp;[https://en.wikipedia.org/wiki/Tetrahymena https://en.wikipedia.org/wiki/Tetrahymena]</span><br/> &nbsp;