共查询到13条相似文献,搜索用时 78 毫秒
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对峡东和邻近地区早寒武世古盘虫类三叶虫的再研究,支持将Emeidiscus Li,1980;Mianxrindiscus S.Zhang et Zhu in Zhang et al,1980;Mianxiandiscus(Liangshandiscus)S.Zhang in Zhang et al.,1980;Hupeidiscus Chang in Lu et al.,1974;Guizhoudiscus S.Zhang in Zhang et al.,1980;Shizhudiscus S.Zhang et Zhu in Zhang et al.,1980等属作为Tsunyidiscus Chang,1966的同义名的意见。并对前人所建立的有关属的种,进行了重新研究和整理,作了大量的归并和修订。就目前所知道,峡东地区早寒武世水井沱组的古盘虫类三叶虫仅有Tsunyidiscus Chang,1966和Sinodiscus Chang in Lu et al,1974两属。Hupeidiscus经修订归入Tsunyidiscus Chang,1966后,原Hebediscus orientalis Chang,1953(即原Hupeidiscus的模式种)一种的种名与Tsunyidiscus orientalis(Walcott,1905)重名,故将前者重新命名为Tsunyidiscus pertenus nom.nov.。文中还记述了湖北宜昌、秭归等地的早寒武世古盘虫类三叶虫2属3种,包括Tsunyidiscus yanjiazhaiensis S.Zhang,Zhou et Yuan in Yin and Li,1978;Tsunyidisacutus(Sun,1983);Sinodiscus changyangensis S.Zhang in Zhou et al.,1977。 相似文献
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The origin of life and the nature of the primitive gene 总被引:4,自引:0,他引:4
A G Cairns-Smith 《Journal of theoretical biology》1966,10(1):53-88
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The structure of a primitive kinetochore 总被引:6,自引:0,他引:6
The isolation of yeast centromeres has provided the opportunity to describe the molecular structure of chromosome attachments to the mitotic spindle. Nucleolytic probes of chromatin structure and construction of conditional mutants in centromere function have been used to study the regulation and assembly of centromeres throughout the cell cycle in Saccharomyces cerevisiae. 相似文献
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Locke M 《Tissue & cell》1985,17(6):901-921
Epidermal cells in Calpodes and other insects form basal processes or feet that at first extend axially and later shorten at the same time as the larval segment shortens to the pupal shape. The feet grow into spaces at the surfaces of other cells to make a basal interlacing meshwork of cellular extensions that are combined mechanically by their desmosomal attachments to cell bodies above and to the basal lamina below. Microtubules and microfilaments are linked to these junctions by a reticular fibrous matrix. Gap junctions on the feet may couple cells that are several cell bodies removed from one another. The meshwork is also a sieve separating the hemolymph from the spaces between cells to form an intercellular compartment. Entry to the intercellular compartment is through the sieve made by the negatively charged basolateral cell surfaces that can prevent the entry of positively charged molecules such as cationic ferritin. As the cells become columnar, coincident with the metamorphic change in segment shape, the feet shorten and pack more densely together. At this time the basal lamina buckles axially as if responding to contraction of the feet. Segment shape change involves cell rearrangement and relative cell movement, necessitating the transient loss of plasma membrane plaque attachments to the cuticle apically and the loss of junctions laterally. Gap junctions involute in characteristic vacuoles. The metamorphic reduction in cell surface area coincides with the loss of basolateral membrane in smooth tubes and vesicles and the turnover of the apical surface in multivesicular bodies. New apical plasma membrane plaques and new lateral and basal junctions stabilize the cells in their pupal positions. 相似文献
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Aldana-González M Cocho G Larralde H Martínez-Mekler G 《Journal of theoretical biology》2003,220(1):27-45
We address the question, related with the origin of the genetic code, of why are there three bases per codon in the translation to protein process. As a follow-up to our previous work (Aldana et al., 1998, Martínez-Mekler et al., 1999a,b), we approach this problem by considering the translocation properties of primitive molecular machines, which capture basic features of ribosomal/messenger RNA interactions, while operating under prebiotic conditions. Our model consists of a short one-dimensional chain of charged particles (rRNA antecedent) interacting with a polymer (mRNA antecedent) via electrostatic forces. The chain is subject to external forcing that causes it to move along the polymer which is fixed in a quasi-one-dimensional geometry. Our numerical and analytic studies of statistical properties of random chain/polymer potentials suggest that, under very general conditions, a dynamics is attained in which the chain moves along the polymer in steps of three monomers. By adjusting the model in order to consider present-day genetic sequences, we show that the above property is enhanced for coding regions. Intergenic sequences display a behavior closer to the random situation. We argue that this dynamical property could be one of the underlying causes for the three-base codon structure of the genetic code 相似文献
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