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  • Life and Medical Sciences
  • 1990-1994
  • 1980-1984
  • 1965-1969  (10)
  • 1940-1944
  • 1915-1919
  • 1969  (10)
Collection
Publisher
Years
  • 1990-1994
  • 1980-1984
  • 1965-1969  (10)
  • 1940-1944
  • 1915-1919
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 74 (1969), S. 239-240 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Assemblies of protein molecules represent a fundamental level of biological organization. The dynamic behavior of these systems-including both the assembly process and functional rearrangements-may be accounted for by the specificity of the protein interactions, which depend on environmental conditions. Analysis of the self-assembly of virus particles has established that the design of an ordered structure can be built into the specific bonding properties of the constituent proteins. Any structure which can change its state of organization is, by definition, polymorphic. The distinctive aspect of polymorphism in protein structures, contrasted with nonliving states of matter, is that the molecular design has been selected to carry out a function and that this function is part of an integrated system. The differences in molecular conformation and arrangement in all polymorphic structures-for example, allosteric enzymes or ice crystals-depend on the intrinsic interaction properties of the molecules themselves. The structures of ice and water illustrate relations between specificity and polymorphism which are relevant to the form and function of protein assemblies.Two types of polymorphism can be distinguished: modal polymorphism, which is externally moderated, as in phase transitions between different crystals forms; and positional polymorphism, which is internally moderated, as in the different disposition of identical molecules within a single crystal lattice. Positional polymorphism, exemplified by the quasi-equivalent bonding of icosahedral virus coat proteins and the different arrangement of myosin and paramyosin at the center and polar portions of the bipolar filaments, results from specific interactions that are not compatible with a strictly equivalent packing of identical molecules. The structural rearrangements in muscle contraction and the switching between the oxy and deoxy forms of hemoglobin represent the formation of different structures in response to altered external conditions. The different structural states of many protein assemblies are characterized by conserved connections which may be regarded as providing the framework for functional rearrangements. The types of polymorphism displayed by hemoglobin, virus, and muscle proteins demonstrate the relevance of the simple view that the function of a protein is determined by the potential structures it can form.
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  • 2
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The complete regeneration of a new oral-disc and tentacles has been observed and described for Aiptasia diaphana. These structures are regenerated quite rapidly: seven to ten days at 20°C. At three days post-amputation, the new primary, secondary, and tertiary tentacle buds begin to develop in direct association with the underlying primary, secondary, and tertiary septae (respectively) of the column, suggesting that the latter organize the form of the regenerating oral-disc. Two days after amputation, the zooxanthellae of the presumptive oral disc arrange themselves into a ring which quite precisely delimits the area from which the tentacle buds will form. In spite of its suggestive proximity, this accumulation of algae plays no role in the induction of tentacle buds as was shown by studying regeneration in anemones which essentially lacked large quantities of these symbiotic algae.Cuts perpendicular to the longitudinal axis of the column result in an equal rate of tentacular regeneration around the entire circumference of the presumptive oral disc. Oblique amputations foster an asynchronous regeneration: the tentacle buds of the distal-most area of the severed column are larger and regenerate much sooner than those of the proximal region. Similar results were obtained by studying anemones which were cut perpendicular to their longitudinal axes at different levels along the column. The data suggest that an oral-aboral gradient exists concerning the time required for the initiation of tentacle budding and the rate of tentacle regeneration.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 127 (1969), S. 363-372 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Using the Colcemid technique, the mitotic incidence (MI) was measured in the epidermis, lung, spleen, liver, kidney and ovarian follicular cells of metamorphosed, immature Xenopus laevis laevis. The MI was higher at 25°C than at 20°C, and there was a significant ranking correlation between organs in respect of the MI in different animals. With the exception of the liver and kidney, organ cultures showed good preservation for up to six days in vitro using a medium supplemented with 10% fetal calf serum, and values for MI comparable with or even higher than in vivo were obtained.
    Additional Material: 2 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 127 (1969), S. 383-407 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The structure of human labial salivary gland acini was studied by light and electron microscopy. Contrary to previous reports, these glands were pure mucous in nature; no serous elements were present. The acinar cells were found in all stages of maturation. Immature cells were characterized by an extensive and highly organized rough-surfaced endoplasmic reticulum. The Golgi complex was extremely prominent, consisting of stacks of flattened cisternae and swarms of small vesicles. Mucous droplets were almost completely absent. As secretory activity progressed, the endoplasmic reticulum involuted, while the Golgi cisternae became distended and formed many vacuoles. In mature mucous cells, the apical cytoplasm was filled with membrane-bounded mucous droplets, and the nucleus was displaced basally. The droplets frequently showed great variation in density from cell to cell, and even within the same cell they sometimes were quite heterogeneous. They were liberated from the acinar cells by an apocrine process, so that droplets with intact limiting membranes were often observed in the acinar lumen. These droplets soon lysed, their contents fusing into streams of mucus. Occasionally during apocrine secretion a mucous cell failed to reconstitute its apical surface, and its entire contents spilled into the acinar lumen.Unusual cytoplasmic inclusions were present in many of the acinar cells. These inclusions, which were surrounded by a single membrane, consisted of lipid droplets closely associated with bundles of fine filaments.
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  • 5
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The fine structure of the mid-gut epithelium and regenerative cells of larvae of a moth (Ephestia kühniella) is described. Particular attention is paid to the absorptive and goblet cells and their lateral junctions; these features are discussed in terms of the digestive and regulatory functions of the epithelium. One digestive pathway has been investigated with the aid of ingested ferritin; intake of this marker by endocytosis and the evident involvement of Golgi vesicles in the transformation of endocytic vesicles into multivesicular bodies, together with the fate of the latter, are discussed in terms of the digestive function of this part of the alimentary tract and of the lysosome concept.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 127 (1969), S. 1-5 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Tooth attachment in the majority of the bony fish is by ankylosis or fibrous membrane. However, in one group of the osteichthys, the trigger-fish or balistids, tooth attachment is by means of a periodontium composed of a shallow alveolar socket, a periodontal ligament and acellular cementum.Histologically, the balistid periodontal ligament is composed of a dense fibro-cellular connective tissue possessing an abundance of typical fibrocytes, collagen fiber bundles, and oxytalan fibers. The collagen fiber bundles which resemble the principal fiber bundles of the mammalian periodontal ligament are inserted into the bone of the shallow alveolar sockets and are anchored to the teeth by means of a layer of amorphous acellular cementum that covers the radicular dentin. No cementoblasts were found in functional teeth, and epithelial rests are lacking. The mid-central zone of the balistid periodontal ligament is occupied by small blood vessels.
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  • 7
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: After the experimental verification of Crick's adaptor hypothesis for the role of tRNA, it became apparent that one of the most important of the protein-nucleic acid interactions occurs at the first step in protein synthesis, namely the amino acid activation reaction. It is here that a specific aminoacyl-tRNA synthetase must select, with high fidelity, a specific tRNA out of a large collection of molecules of similar size, shape, and overall composition. A mistake at this point, either by esterification of the wrong amino acid to the correct tRNA or by selection of the wrong tRNA, will inevitabley result in the insertion of an amino acid at an incorrect position in a growing polypeptide. Although there are known rules that dictate how one nucleic acid can recognize and interact with another nucleic acid, nothing is known regarding the mechanism by which a specific protein can recognize and interact with a specific nucleic acid. In order to gain some insight into the specific recognition between an aminoacyl-tRNA synthetase and its cognate tRNA, it became necessary to study the specific interaction with highly purified materials, preferably in gram quantities. An effort to do this for both the synthetases and the tRNA's was launched at the Oak Ridge National Laboratory about 6 years ago. Four high-resolution column chromatographic procedures have been developed in the ORNL Macromolecular Separations Program for the separation and production of highly purified species of tRNA's. An unexpected “spin-off” from this program is the analytical use of some of these systems to detect qualitative changes in the tRNA profile of cells as a consequence of virus infection, methionine starvation, and other metabolic alterations.Some examples of the heterologous interaction between aminoacyl-tRNA synthetases of one species with the tRNA's of another species, and some of the inherent dangers in the interpretation of such interactions, are considered.Finally, some speculations are made regarding the possible role of tRNA in regulation.
    Additional Material: 21 Ill.
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  • 8
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The fraction of cell capable of division was determined for (1) population of the human diploid cell strains, WI38 after different numbers of subcultivations in vitro and (2) a single population of WI38 cells at intervals throughout its entire in vitro lifespan. In both cases the percentage of cells capable of division decreased with increasing age in tissue culture. The rate and the magnitude of the decrease is sufficient to account for the limited in vitro lifespan reported by other investigators. Furthermore, the decrease in the fraction of cells capable of division in similar in some respects of senescence among human populations.
    Additional Material: 2 Ill.
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  • 9
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Growth hormone, oxytocin, parathyroid hormone, prolactin and lysine vasopressin strongly stimulate mitotic activity in rat thymocyte populations maintained in vitro. These hormones have no mitotic effect on cells maintained in calcium-free medium. It is concluded that they stimulate mitosis only indirectly by sensitising the mitotically competent segment of a thymocyte population to the action of calcium. The stimulatory action of calcium itself is opposed by low concentrations of the mucopolysaccharide chondroitin sulphate. However, the inhibitory action of chondroitin sulphate can be overcome by growth hormone.A possible common mechanism of action of these hormones on mitotically competent cells is discussed.
    Additional Material: 9 Ill.
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  • 10
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The progression of rat thynocytes (maintained in vitro) into mitosis is profoundly affected by the level of magnesium in the medium. Increasing the extracellular MgC12 concentration from 0 to 1.0 mM does not affect mitotic activity, but a further increase to 1.2 and 2.5 mM rapidly and strongly stimulates the flow of cells into mitosis. The level of extracellular magnesium also governs the mitogenic effectiveness of calcium ions. The mitogenic action of magnesium stems from an ability to stimulate the initiation of deoxyribonucleic acid synthesis.
    Additional Material: 6 Ill.
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