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Plenarvorträge - DPG-Tagungen

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Arbeitskreis Biologische Physik Freitag<br />

AKB 50.95 Fr 10:30 B<br />

Global pattern formation from local cell-to-cell communication<br />

— •Thimo Rohlf and Stefan Bornholdt — IZBI, University of<br />

Leipzig, Kreuzstr. 7b, 04103 Leipzig, Germany<br />

A central observation in developmental biology is the self-organization<br />

of spatial gene expression patterns on scales much larger than cell size. In<br />

existing models, this is often explained by morphogen gradients, which<br />

are established by Turing instability of activator-inhibitor systems [1].<br />

However, pattern formation in these models depends on parameter tuning<br />

of, e.g., diffusion constants. The role of gene regulation in development<br />

is neglected. Here we sketch a new process of global pattern formation<br />

from local information transfer without the need for parameter tuning.<br />

We study a three-state cellular automaton which reproduces two basic<br />

experimental observations at the polyp Hydra: de novo pattern regeneration<br />

and regulation of expression domain size proportional to system<br />

size.<br />

The model shows remarkable robustness with respect to noise and cell<br />

movement. Similar mechanisms could in principle occur in biological organisms<br />

where direct contact induction is present.<br />

[1] Gierer, A. and Meinhardt, H., Kybernetik 12, 30 (1972)<br />

AKB 50.96 Fr 10:30 B<br />

A biological solar energy generator — •Dieter F. Ihrig 1 , H.<br />

Michael Heise 2 , Alexander Moor 2 , Manuel Gemuend 1 , Darius<br />

Wilczek 1 , Ruediger Kuckuk 2 , and Martin Poschmann 1 —<br />

1 FH Suedwestfalen Iserlohn, Germany — 2 Institut fuer Spektrochemie<br />

und angewandte Spektrometrie, Dortmund, Germany<br />

Biomass production by micro algae is by a factor of 10 more efficient<br />

then plants. This gives the chance to create an economic process of solar<br />

energy harvesting. In view of the very low dry mass content of algal<br />

suspensions the most promising way of conversion to a high exoergic and<br />

transportable form of energy is the anearobic production of biogas.<br />

We are actually developing such processes especially micro algal reactors,<br />

a method to separate micro algal cells, a method to treat the micro<br />

algal biomass and a two stage anaerobic process. First results of these<br />

project sections are shown. The developed anaerobic process is very efficient<br />

but also very unstable. To get a better process management it is<br />

necessary to understand the influences between the parameters of process<br />

engineering and biochemical parameters like the concentration of<br />

carboxylic acids. Goal of this part of the project is the development of<br />

an inline sensor. The project was funded by the German Federal Ministry<br />

for Education and Research (BMBF).<br />

AKB 50.97 Fr 10:30 B<br />

FCS used to study translational mobilities in plasma membranes<br />

of living cells — •Margarita Khazarchyan 1 , Elmar<br />

Thews 1 , Carsten Tietz 1 , Jörg Wrachtrup 1 , Sylvia Willi 2 ,<br />

Anja Krippner-Heidenreich 2 , and Peter Scheurich 2 —<br />

1 3.Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring<br />

57, 70569 Stuttgart — 2 Institut für Zellbiologie und Immunologie,<br />

Universität Stuttgart, Allmandring 31, 70569 Stuttgart<br />

Fluorescence correlation spectroscopy (FCS) is an attractivce method<br />

of measuring molecular concentrations, chemical kinetics and diffusion<br />

processes in living cells. We use one- and two-photon excitation for the<br />

investigation of translational mobility in cytoplasm and in plasma membranes<br />

using different fluorophores for intracellular applications of FCS.<br />

Measurements in living cells and in plasma membranes are feasible with<br />

reasonable signal-to-noise ratios, even with fluorophore concentrations on<br />

a single molecule level in the detection volume.<br />

We present an application of this method to study TNF(Tumor Necrosis<br />

Factor)-R1, TNF-R2 in plasma membranes and TRAF2-protein in<br />

cytoplasm of living cells. Other investigations demonstrated that TNF-R<br />

and TRAF-proteins involved in the cells apoptotic pathway. Apoptosis is<br />

the specific controlled mechanism of cell death which is distinct from uncontrolled<br />

necrotic cell death. Apoptosis requires tight regulation. Lack of<br />

such regulation leads to either too much or too little apoptosis, resulting<br />

in pathological conseqeunces, such as Alzheimer disease or cancer.<br />

Diffusion coefficients of the signal TNF-R and TRAF2-protein were<br />

determined before and after stimulation with TNF ligand.<br />

AKB 50.98 Fr 10:30 B<br />

Stepwise rotation of the epsilon-subunit of EFoF1-ATP synthase<br />

during ATP synthesis and hydrolysis - a single-molecule<br />

FRET approach — •Michael Börsch 1 , Boris Zimmermann 2 ,<br />

Nawid Zarrabi 1 , Manuel Diez 2 , and Peter Gräber 2 —<br />

1 3. Physikalisches Institut, Universität Stuttgart — 2 Institut für<br />

Physikalische Chemie, Universität Freiburg<br />

F-type ATP synthases catalyze the formation of ATP by coupling<br />

two rotary motions of subunits within the enzyme. We attached<br />

tetramethylrhodamine-maleimide at the rotating epsilon-subunit and<br />

Cy5-bismaleimide crosslinking the two b-subunits, and reconstituted the<br />

enzymes fully functional into liposomes. Fluorescence resonance energy<br />

transfer (FRET) was monitored in photon bursts of freely diffusing ATP<br />

synthases with a confocal setup for single-molecule detection. Incubation<br />

with non-hydrolysable AMPPNP resulted in stable intensity ratios<br />

within a burst and three different FRET efficiencies corresponding to<br />

the three possible orientations of the epsilon-subunit.<br />

Upon addition of ATP at mM concentrations, a consecutive order of<br />

three distinguishable FRET efficiencies was observed indicating a stepwise<br />

movement of the epsilon-subunit, comparable to the stepwise rotation<br />

of the gamma-subunit in EFoF1 [1,2]. Under the conditions for ATP<br />

synthesis stepwise rotation of the epsilon-subunit was observed in opposite<br />

direction. Dwell-time analysis revealed heterogeneity of the three<br />

catalytic binding sites.<br />

[1] M. Borsch et al. (2002) FEBS lett. 527, 147-152.<br />

[2] M. Diez et al. (2004) Nat. Struct. Mol. Biol., in press.<br />

AKB 50.99 Fr 10:30 B<br />

DNA translocation through a biological nanopore — •Ulrich F.<br />

Keyser 1 , N. Wennersbusch 1 , D. J. Bonthuis 1 , N. H. Dekker 1 ,<br />

X. S. Ling 2 , and Cees Dekker 1 — 1 Molecular Biophysics, Delft University<br />

of Technology, Lorentzweg , 2628 CJ Delft, The Netherlands1 —<br />

2 Brown University, Providence, USA<br />

We study the translocation of single-stranded DNA (ss-DNA)<br />

molecules through a single biological nanopore, viz., an alpha-Hemolysin<br />

pore from Staphylococcus aureus assembled within a lipid membrane.<br />

The inner diameter of this nanopore is only 1.5 nm and ss-DNA molecules<br />

can be transferred one by one. Applying a bias voltage at high salt concentrations<br />

gives rise to an ionic current through the nanopore. If a ss-DNA<br />

molecule enters the pore the current is partly blocked and the passage<br />

of a molecule is detected. We are investigating different types of ss-DNA<br />

with various lengths and sequences to study the influence on the translocation<br />

speed and current. The experimental results will be compared to<br />

recent theoretical models.<br />

AKB 50.100 Fr 10:30 B<br />

Immobilisation of the Light harvesting complex LH1 of<br />

Rhodospirillum rubrum on nanostructured surfaces — •Britta<br />

Götze, Carsten Tietz, and Jörg Wrachtrup — 3. Physikalisches<br />

Institut, Universität Stuttgart, Germany<br />

Sunlight is the driving force on this planet. To make it useable plants<br />

and bacteria have created a sofisticated system- the photosynthetic apparatus<br />

-.The final product of this system is ATP - the most common<br />

transporter of energy in every living thing.<br />

The first step in this apparatus is to capture sunlight as excitation<br />

energy and transfer it to the reaction center. Here a charge seperation<br />

takes place as a initializing step in photosynthesis.<br />

In this work the light harvesting complex LH1, a pigment protein complex<br />

of the purple bacterium Rhodospirillum rubrum is investigated. The<br />

studies have been performed on nanostructured as well as on modified<br />

surfaces. The aim of this work is to investigate the possibility of long<br />

range 1d energy transfer between light harvesting complexes on nanostructured<br />

surfaces.<br />

The structures are made using electron beam lithography and consist<br />

of gold/titanium on SiO2. A self assembled monolayer is formed on top<br />

of them using different types of mercaptanes.<br />

First step was to figure out what kind of mercaptane offers the best adsorbance<br />

properties for the light harvesting complexes./par Second step<br />

was to proof a specific binding / adsorbance of the proteins on the modified<br />

surface./par Third step will be to get a densly package of proteins<br />

on these structures.

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