Global ETD Search

11	Physical Aspects of Min Oscillations in Escherichia Coli Meacci, Giovanni 25 January 2007 (has links) (PDF) The subject of this thesis is the generation of spatial temporal structures in living cells. Specifically, we studied the Min-system in the bacterium Escherichia coli. It consists of the MinC, the MinD, and the MinE proteins, which play an important role in the correct selection of the cell division site. The Min-proteins oscillate between the two cell poles and thereby prevent division at these locations. In this way, E. coli divides at the center, producing two daughter cells of equal size, providing them with the complete genetic patrimony. Our goal is to perform a quantitative study, both theoretical and experimental, in order to reveal the mechanism underlying the Min-oscillations. Experimentally, we characterize theMin-system, measuring the temporal period of the oscillations as a function of the cell length, the time-averaged protein distributions, and the in vivo Min-protein mobility by means of different fluorescence microscopy techniques. Theoretically, we discuss a deterministic description based on the exchange of Minproteins between the cytoplasm and the cytoplasmic membrane and on the aggregation current induced by the interaction between membrane-bound proteins. Oscillatory solutions appear via a dynamic instability of the homogenous protein distributions. Moreover, we perform stochastic simulations based on a microscopic description, whereby the probability for each event is calculated according to the corresponding probability in the master equation. Starting from this microscopic description, we derive Langevin equations for the fluctuating protein densities which correspond to the deterministic equations in the limit of vanishing noise. Stochastic simulations justify this deterministic model, showing that oscillations are resistant to the perturbations induced by the stochastic reactions and diffusion. Predictions and assumptions of our theoretical model are compatible with our experimental findings. Altogether, these results enable us to propose further experiments in order to quantitatively compare the different models proposed so far and to test our model with even higher precision. They also point to the necessity of performing such an analysis through single cell measurements. Min-Protein-Oscillations biochemical reactions Theory and modeling: computer simulation cell growth and division Fluorescence Correlation Spectroscopy Protein mobility Fluctuation phenomena random process noise self-organaized systems pattern fo Min-Protein-Oszillationen biochemische Reaktionen Zellwachstum und -teilung Spektroskopie Mobilitaet von Proteinen Fluktuationen stochastische Prozesse Rauschen selbstorganisierte Systeme Musterbild ddc:570 rvk:WG 1700 Escherichia Coli Biologische Oszillation Biochemische Reaktion Computersimulation Zellwachstum Zellteilung Musterbildung
12	Spatio-Temporal Dynamics of Pattern Formation in the Cerebral Cortex / Visual Maps, Population Response and Action Potential Generation / Raum-zeitliche Dynamik der Musterbildung in der kortikalen Großhirnrinde / Visuelle Karten, Populationsantwort und Enstehung der Aktionspotentiale Huang, Min 24 April 2009 (has links) No description available. 500 Naturwissenschaften Orientierungspräferenzkarte selbstorganisierte Feature-Karte Aktionpotential Phasendarstellung multi-Kompartment Modelle Hodgkin-Huxley Modelle Orientation Preference Map SOFM Action Potential phase plot multi-compartment model Hodgkin-Huxley model 42.10 42.12 WC 000: Biophysik WD 000: Bioinformatik {Biologie}
13	A Self-Assembled Matrix System for Cell-Bioengineering Applications in Different Dimensions, Scales, and Geometries Xu, Yong, Patino Gaillez, Michelle, Zheng, Kai, Voigt, Dagmar, Cui, Meiying, Kurth, Thomas, Xiao, Lingfei, Wieduwild, Robert, Rothe, Rebecca, Hauser, Sandra, Lee, Pao-Wan, Lin, Weilin, Bornhäuser, Martin, Pietzsch, Jens, Boccaccini, Aldo R., Zhang, Yixin 22 April 2024 (has links) Stem cell bioengineering and therapy require different model systems and materials in different stages of development. If a chemically defined biomatrix system can fulfill most tasks, it can minimize the discrepancy among various setups. By screening biomaterials synthesized through a coacervation-mediated self-assembling mechanism, a biomatrix system optimal for 2D human mesenchymal stromal cell (hMSC) culture and osteogenesis is identified. Its utility for hMSC bioengineering is further demonstrated in coating porous bioactive glass scaffolds and nanoparticle synthesis for esiRNA delivery to knock down the SOX-9 gene with high delivery efficiency. The self-assembled injectable system is further utilized for 3D cell culture, segregated co-culture of hMSC with human umbilical vein endothelial cells (HUVEC) as an angiogenesis model, and 3D bioprinting. Most interestingly, the coating of bioactive glass with the self-assembled biomatrix not only supports the proliferation and osteogenesis of hMSC in the 3D scaffold but also induces the amorphous bioactive glass (BG) scaffold surface to form new apatite crystals resembling bone-shaped plate structures. Thus, the self-assembled biomatrix system can be utilized in various dimensions, scales, and geometries for many different bioengineering applications. info:eu-repo/classification/ddc/570 ddc:570 info:eu-repo/classification/ddc/620 ddc:620
14	Dynamics of Cilia and Flagella / Bewegung von Zilien und Geißeln Hilfinger, Andreas 14 January 2006 (has links) (PDF) Cilia and flagella are hair-like appendages of eukaryotic cells. They are actively bending structures that exhibit regular beat patterns and thereby play an important role in many different circumstances where motion on a cellular level is required. Most dramatic is the effect of nodal cilia whose vortical motion leads to a fluid flow that is directly responsible for establishing the left-right axis during embryological development in many vertebrate species, but examples range from the propulsion of single cells, such as the swimming of sperm, to the transport of mucus along epithelial cells, e.g. in the ciliated trachea. Cilia and flagella contain an evolutionary highly conserved structure called the axoneme, whose characteristic architecture is based on a cylindrical arrangement of elastic filaments (microtubules). In the presence of a chemical fuel (ATP), molecular motors (dynein) exert shear forces between neighbouring microtubules, leading to a bending of the axoneme through structural constraints. We address the following two questions: How can these organelles generate regular oscillatory beat patterns in the absence of a biochemical signal regulating the activity of the force generating elements? And how can the beat patterns be so different for apparently very similar structures? We present a theoretical description of the axonemal structure as an actively bending elastic cylinder, and show that in such a system bending waves emerge from a non-oscillatory state via a dynamic instability. The corresponding beat patterns are solutions to a set of coupled partial differential equations presented herein. Axonem Bewegung bei kleinen Reynolds Zahlen Biophysik Flagellen Geißeln Molekulare Motoren Nodale Zilien Physik Selbstorganisierte Schlagmuster Situs inversus Spermien Wimpern Zilien Situs inversus axoneme biophysics cilia dynein flagella left-right axis formation low Reynolds number dynamics molecular motors nodal cilia physics spermatozoa spontaneous oscillations ddc:530 rvk:UF 5000 Cilie Flagelline Geißel &lt;Biologie&gt; Molekularer Motor Reynolds-Zahl Selbstorganisation Spermium Zilie
15	Dynamics of Cilia and Flagella Hilfinger, Andreas 07 February 2006 (has links) Cilia and flagella are hair-like appendages of eukaryotic cells. They are actively bending structures that exhibit regular beat patterns and thereby play an important role in many different circumstances where motion on a cellular level is required. Most dramatic is the effect of nodal cilia whose vortical motion leads to a fluid flow that is directly responsible for establishing the left-right axis during embryological development in many vertebrate species, but examples range from the propulsion of single cells, such as the swimming of sperm, to the transport of mucus along epithelial cells, e.g. in the ciliated trachea. Cilia and flagella contain an evolutionary highly conserved structure called the axoneme, whose characteristic architecture is based on a cylindrical arrangement of elastic filaments (microtubules). In the presence of a chemical fuel (ATP), molecular motors (dynein) exert shear forces between neighbouring microtubules, leading to a bending of the axoneme through structural constraints. We address the following two questions: How can these organelles generate regular oscillatory beat patterns in the absence of a biochemical signal regulating the activity of the force generating elements? And how can the beat patterns be so different for apparently very similar structures? We present a theoretical description of the axonemal structure as an actively bending elastic cylinder, and show that in such a system bending waves emerge from a non-oscillatory state via a dynamic instability. The corresponding beat patterns are solutions to a set of coupled partial differential equations presented herein. info:eu-repo/classification/ddc/530 ddc:530
16	Physical Aspects of Min Oscillations in Escherichia Coli Meacci, Giovanni 20 December 2006 (has links) The subject of this thesis is the generation of spatial temporal structures in living cells. Specifically, we studied the Min-system in the bacterium Escherichia coli. It consists of the MinC, the MinD, and the MinE proteins, which play an important role in the correct selection of the cell division site. The Min-proteins oscillate between the two cell poles and thereby prevent division at these locations. In this way, E. coli divides at the center, producing two daughter cells of equal size, providing them with the complete genetic patrimony. Our goal is to perform a quantitative study, both theoretical and experimental, in order to reveal the mechanism underlying the Min-oscillations. Experimentally, we characterize theMin-system, measuring the temporal period of the oscillations as a function of the cell length, the time-averaged protein distributions, and the in vivo Min-protein mobility by means of different fluorescence microscopy techniques. Theoretically, we discuss a deterministic description based on the exchange of Minproteins between the cytoplasm and the cytoplasmic membrane and on the aggregation current induced by the interaction between membrane-bound proteins. Oscillatory solutions appear via a dynamic instability of the homogenous protein distributions. Moreover, we perform stochastic simulations based on a microscopic description, whereby the probability for each event is calculated according to the corresponding probability in the master equation. Starting from this microscopic description, we derive Langevin equations for the fluctuating protein densities which correspond to the deterministic equations in the limit of vanishing noise. Stochastic simulations justify this deterministic model, showing that oscillations are resistant to the perturbations induced by the stochastic reactions and diffusion. Predictions and assumptions of our theoretical model are compatible with our experimental findings. Altogether, these results enable us to propose further experiments in order to quantitatively compare the different models proposed so far and to test our model with even higher precision. They also point to the necessity of performing such an analysis through single cell measurements. info:eu-repo/classification/ddc/570 ddc:570

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