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Query: UMLS:C0276640 (TEM)
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Normal and denatured polytene chromosomes from Drosophila were compared by light, transmission (TEM) and scanning (SEM) electron microscopy, under different conditions of pretreatment, fixation and specimen preparation. Apart from variations in contrast, acid-alcohol squashes of normal chromosomes were quite comparable in terms of resolution and image quality, regardless of mode of visualization, i.e. stained, unstained, phase contrast, etc. These chromosomes do not appear markedly different from the unfixed or "native" chromosomes isolated by other workers. Thus at the light microscope level at least, any soluble components extracted by acid-alcohol fixation seem to play minor structural roles only. SEM examination of similar squash preparations provided useful topographic views of selected chromosome regions, particularly in favourable spreads where metal coating and tilt angles were optimized. Information on the internal organization of polytene chromosomes was sought by subjecting isolated preparations to alkali-urea denaturation. Under these conditions, chromosomes gradually extend laterally to give rise to lampbrush-like structures, remarkably similar to the meiotic chromosomes of amphibian oocytes. This effect is at least partially reversed by return of alkali-urea treated preparations to physiological Ringer solution, where chromosomes contract again and near-normal banding patterns are re-established. It is suggested that apart from bulk differences due to polyteny, the basic structure of polytene chromosomes and true lampbrush chromosomes may be rather similar.
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PMID:The morphology of normal and denatured polytene chromosomes from Drosophila melanogaster. 9 84

Attempts to promote crystal growth in maturation stage enamel from rat incisors were carried out by incubation in saturated solutions of calcium phosphate. Resulting crystallites were visualised in the TEM and the dimensions of their profiles measured. No crystal growth was observed unless the maturation stage enamel was first pretreated with either 8M urea or sodium hypochlorite to remove residual protein matrix. The results suggest that the protein matrix plays an important role in the control of crystal growth in vivo.
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PMID:Control of crystal growth during enamel maturation. 259 65

Transmission (TEM) and scanning (SEM) electron microscopic studies were performed on the human sperm heads extracted with (a) 1% Triton X-100, 1% mercaptoethanol (ME) and (b) 8 M urea, 1% ME together with increasing concentrations of NaCl ranging from 0.2 to 0.6 M. In the TEM study, the extraction of the nuclear material was first observed when the heads were treated with 8 M urea and 1% ME, with the majority of the chromatin remaining as 400-550 A thick interconnecting cords and oval bodies. At 0.2 M NaCl the cords and bodies were further separated but linked together by extremely thin 20-50 A fibers. Between 0.3 and 0.5 M NaCl the chromatin bodies within the sperm heads began to be extracted, first at the central part and progressively towards the periphery. Finally, at 0.6 M NaCl only the chromatin cords forming the periphery of the heads remained. In the SEM study, the sperm heads remained unbroken up to the treatment with 8 M urea, 1% ME and 0.2 M NaCl. Between 0.3 M and 0.5 M NaCl the majority of heads were disrupted to form interlacing chromatin cords of 400-550 A thick while the unbroken heads exhibited surface with cross-weaving cords. At 0.6 M NaCl all heads were disrupted and the remaining chromatin existed mostly as exoskeleton of former sperm heads. Protein gel electrophoresis showed that histones and nonhistones were removed from the chromatin when the treatment reached 0.2 M NaCl, whereas protamines started to be removed at 0.3 M, and totally removed at 0.6 M NaCl; HP1 was the first protamine fraction to be extracted.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Transmission and scanning electron microscopic studies of human sperm heads extracted with 8 M urea, 1% mercaptoethanol and different concentrations of salt. 639 79

Upregulating hepatocyte function in proliferating human liver cell lines could provide cells for a bio-artificial liver. Ideally, a means of mimicking the biological extracellular matrix with a relatively inert, bio-compatible matrix is required. Alginate encapsulation of primary hepatocytes is biocompatible. This study aimed to characterize cells grown in a 3D configuration in alginate. A human-derived liver cell line encapsulated in 1% alginate was assessed for synthetic and detoxification functions. Secreted proteins measured (e.g., albumin, fibrinogen, alpha-1-antitrypsin etc.) were increased in alginate compared with monolayers. Cytochrome P450 1A1 activity increased three- to fourfold, whilst urea synthesis, undetectable in monolayer cultures, was synthesized by cells in alginate at levels approaching in vivo production. TEM revealed good ultrastructure reminiscent of normal hepatocytes. Alginate promotes 3D colonies of proliferating cells with upregulated liver functions. Rapid recovery of function of cryopreserved cells (< 18 h) provides added advantages for this system to support the biological component of an artificial liver for patients with fulminant hepatic failure.
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PMID:Three-dimensional in vitro cell culture leads to a marked upregulation of cell function in human hepatocyte cell lines--an important tool for the development of a bioartificial liver machine. 1041 81

TolAI--II--beta-lactamase, a fusion protein consisting of the inner membrane and transperiplasmic domains of TolA followed by TEM--beta-lactamase associated with the inner membrane but remained confined to the cytoplasm when expressed at high level in Escherichia coli. Although the fusion protein was resistant to proteolysis in vivo, it was hydrolyzed during preparative SDS-polyacrylamide electrophoresis and when insoluble cellular fractions unfolded with 5 M urea were subjected to microdialysis. Inhibitor profiling studies revealed that both a metallo- and serine protease were involved in TolAI--II--beta-lactamase degradation under denaturing conditions. The in vitro degradation rates of the fusion protein were not affected when insoluble fractions were harvested from a strain lacking protease IV, but were significantly reduced when microdialysis experiments were conducted with material isolated from an isogenic ftsH1 mutant. Adenine nucleotides were not required for degradation, and ATP supplementation did not accelerate the apparent rate of TolAI--II--beta-lactamase hydrolysis under denaturing conditions. Our results indicate that the metalloprotease active site of FtsH remains functional in the presence of 3--5 M urea and suggest that the ATPase and proteolytic activities of FtsH can be uncoupled if the substrate is sufficiently unstructured. Thus, a key role of the FtsH AAA module appears to be the net unfolding of bound substrates so that they can be efficiently engaged by the protease active site.
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PMID:Escherichia coli FtsH (HflB) degrades a membrane-associated TolAI-II-beta-lactamase fusion protein under highly denaturing conditions. 1123 95

A new approach for the morphological control of bridged silsesquioxanes has been achieved by the hydrolysis of silylated organic molecules bearing urea groups. The urea groups are responsible for the auto-association of the molecules through intermolecular hydrogen-bonding interactions. The self-assembly leads to supramolecular architectures that have the ability to direct the organization of hybrid silicas under controlled hydrolysis. The hydrolysis of the chiral diureido derivatives of trans-(1,2)-diaminocyclohexane 1 under basic conditions has been examined. The solid-state NMR spectra ((29)Si and (13)C) showed the hybrid nature of these materials with wholly preserved S-C bond covalent bonds throughout the silicate network. Hybrid silicas with hollow tubular morphologies were obtained by the hydrolysis of the enantiomerically pure compounds, (R,R)-1 or (S,S)-1, whereas the corresponding racemic mixture, rac-1, led to a hybrid with ball-like structures. The tubular shape is likely to result from a combination of two phenomena: the auto-association abilities and a self-templating structuration of the hybrid materials by the organic crystalline precursor. Electronic microscopy techniques (SEM and TEM) gave evidence for the self-templating pathway. The formation of the ball-like structures occurs through a usual nucleation growth phenomenon owing to a higher solubility of the corresponding crystals in the same medium.
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PMID:Shape-controlled bridged silsesquioxanes: hollow tubes and spheres. 1265 58

The development of morphology and mechanical properties of PUU in bulk prepolymer polymerization process was investigated by TEM and in situ FTIR. The data from the FTIR spectra showed that the absorbance of NH band was becoming sharp and its band sites shifted to lower wavenumbers with the increase of reaction time, the absorbance of free urethance carbonyl kept nearly constant at low conversion, and then became weaker, and finally became little because of strong hydrogen bond affect of more and more new wrealink group at high conversion. With increasing of the reaction time, the band sites of urea carbonyl also shifted to the lower wavenumbers and at the same time, the absorbance of ordered urea carbonyl became sharper and sharper. The carbonyl bands vibration models available during curing process were further assigned. The photos of TEM showed that the domains of hard segments became clearer with buildup of hydrogen bond between urealinks.
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PMID:[Development of morphology and mechanical properties in polyurethane-urea(PUU) curing process]. 1293 27

A class of bis-urea compounds with perylene bisimide was synthesized and characterized successfully. (1)H NMR and fluorescence spectra confirmed that strong hydrogen-bonding interactions between neighboring urea groups were formed. Interestingly, the photocurrent measurement showed that the self-assembled films of bis-urea compounds could produce steady and rapid anodic photocurrent responses. The TEM images indicated that well-defined nanoscale rods with uniform diameter distribution could be fabricated by self-assembly of hydrogen-bonding interactions and pi-pi stacking interactions of perylene rings.
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PMID:Assembly and characterization of novel hydrogen-bond-induced nanoscale rods. 1560 37

The synthesis of four bis(trialkoxysilylated) organic molecules capable of self-assembly--(EtO)3Si(CH2)3NHCONH-(CH2)n-NHCONH(CH2)3Si(OEt)3 (n = 9-12)--associating urea functional groups and alkylidene chains of variable length is described. These compounds behave as organogelators, forming supramolecular assemblies thanks to the intermolecular hydrogen bonding of urea groups. Whereas fluoride ion-catalysed hydrolysis in ethanol in the presence of a stoichiometric amount of water produced amorphous hybrids, acid-catalysed hydrolysis in an excess of water gave rise to the formation of crystalline lamellar hybrid materials through a self-organisation process. The structural features of these nanostructured organic/inorganic hybrids were analysed by several techniques: attenuated Fourier transformed infrared (ATR-FTIR), solid-state NMR spectroscopy (13C and 29Si), scanning and transmission electron microscopy (SEM and TEM) and powder X-ray diffraction (PXRD). The reaction conditions, the hydrophobic properties of the long alkylidene chains and the hydrogen-bonding properties of the urea groups are determining factors in the formation of these self-assembled nanostructured hybrid silicas.
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PMID:Lamellar bridged silsesquioxanes: self-assembly through a combination of hydrogen bonding and hydrophobic interactions. 1566 78

The internally fertilizing primitive frog Ascaphus truei (family Ascaphidae) from the Pacific Northwest is the only frog with an intromittent organ. The more advanced neobatrachian frog Eleutherodactylus coqui (family Leptodactylidae) from Puerto Rico has secondarily acquired internal fertilization but mates by cloacal apposition. Nonetheless, both frogs have introsperm with an elongated head containing highly condensed chromatin. Characterization of sperm nuclear basic proteins (SNBPs) in E. coqui by acid-urea polyacrylamide gel electrophoresis indicates that, as in A. truei, testes from a single animal contain several protamines. Amino acid analysis indicates a composition for the most rapidly moving protamine of each species as follows: in E. coqui, ARG (35.6 mol %) + LYS (3.8 mol %) + HIS (7.6 mol %) = 47 mol % total basic residues and in A. truei, ARG (42.1 mol %) + LYS (11.1 mol %) = 53.2 mol % total basic residues. Transmission electron microscopy shows that E. coqui introsperm, like those in A. truei, are elongate with highly condensed chromatin. However, E. coqui introsperm lacks an axial perforatorium that extends into an endonuclear canal. These morphological features are plesiomorphic (primitive) and shared by A. truei with urodeles and basal amniotes (Jamieson et al. (1993) Herpetologica 49:52-65). In E. coqui introsperm, the nucleoprotein complex has a cross-sectional axis of 420 + 20 angstroms and shows a knobby chromatin structural organization in TEM. The presence of arginine-enriched protamines in both a basal anuran like the ascaphid A. truei and a more advanced neobatrachian like the leptodactylid E. coqui supports the hypothesis that internal fertilization acts as a constraint on the range of SNBP diversity in animals.
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PMID:Protamines in the internally fertilizing neobatrachian frog Eleutherodactylus coqui. 1569 90


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