Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Freitag
and give us a better understanding about fusion in biological membranes.
In the second case, we study the fusion of GUVs made of neutral lipid
or diblock copolymer when subjected to electric pulses. We estimate the
characteristic times related to the evolution of the fusion neck. In comparison
to lipid GUVs, polymer vesicles show much slower relaxation due
to the high surface viscosity of their membrane.
In both cases, we detect that the fusion process takes place on the time
scale less than half a millisecond.
AKB 50.55 Fr 10:30 B
Bestimmung der intra- und extraneuronalen Eisenkonzentration
im Gehirn mittels Ionenstrahlanalytik — •Christoph
Meinecke 1 , Tilo Reinert 1 , Markus Morawski 2 , Thomas
Arendt 2 und Tilman Butz 1 — 1 Universität Leipzig; Abteilung
Nukleare Festkörperphysik, Linnestr. 5 , 04103 Leipzig — 2 Paul-Flechsig-
Institut für Hirnforschung, Abteilung Neuroanatomie, Jahnallee 59 ,
04109 Leipzig
”The gain in brain is mainly in the stain” galt lange Zeit für die
Untersuchung neurodegenerativer Krankheiten. Allerdings sind die
Färbemethoden für quantitative Aussagen nur bedingt brauchbar.
Hingegen erlauben neue physikalische Methoden quantitative Analysen
biologischer Materialien. Zum Beispiel bietet die moderne Ionenstrahlanalytik
quantitative ortsaufgelöste Konzentrationsanalysen auf
zellulärer und subzellulärer Ebene.
Bei der Untersuchung von Gehirnschnitten mittels Ionenstrahlanalytik
wurde erstmals die Eisenkonzentration intra- und extraneuronal in
der Substantia nigra Pars compacta und Pars reticulata bei Menschen
quantitativ bestimmt, die an Parkinson erkrankt waren, und mit der Eisenkonzentration
in Hirnschnitten von gesunden Menschen verglichen.
Die Vorteile der Ionenstrahlanalytik (hier PIXE und RBS) sind dabei
die hohe Ortsauflösung von circa 1 µm und die geringe Nachweisgrenze
für Eisen im Bereich von circa 0,05 mmol/l (entspricht 3,7 µg/g des
eingebetteten Gehirnschnittes).
AKB 50.56 Fr 10:30 B
Diffusion in Inhomogeneous Monolayers as Biomimetic
Membranes — •Carsten Selle 1 , Florian Rückerl 1 , Douglas
S. Martin 2 , Martin B. Forstner 2 , Natalie Bordag 1 ,
Marlis Wilke 1 , and Josef Käs 1,2 — 1 Fakultaet fuer Physik und
Geowissenschaften, Universitaet Leipzig — 2 University of Texas at
Austin
Lateral diffusion within membranes plays an important role for essential
cellular processes as, e.g., membrane formation and inter- / intracellular
signalling. We model the diffusion of a protein represented by a
charged polystyrene latex within a lipid monolayer at the air-water interface
mimicking a cell membrane with spatial inhomogeneities - e.g. lipid
rafts - on an expanded scale. For this purpose, the motion of carboxylated
polystyrene latexes diffusing in simple lipid monolayers (pure a)
dimyristoyl phosphatidylethanolamine, DMPE and b) methyl palmitate)
on aqueous subphases has been tracked. We observed that the diffusion
of the particles is apparently influenced by the presence of liquid condensed
domains. Presumably, dipolar interactions between the domains
and the charged particles induce this behavior. This motion was qualitatively
modeled by Monte Carlo simulations.
Furthermore, we study the effect of the antimicrobial peptide Gramicidin
S on the phase behavior and the diffusion properties of the model
systems mentioned above.
AKB 50.57 Fr 10:30 B
Production and Mechanical Properties of Designed Porous
Ceramic Scaffolds — •Alexander Woesz 1,2 , Monika Rumpler 3 ,
Juergen Stampfl 4 , Franz Varga 3 , Nadja Fratzl-Zelman 3 ,
Paul Roschger 3 , Klaus Klaushofer 3 , and Peter Fratzl 1,2 —
1 Max Planck Institute of Colloids and Interfaces, Dept. of Biomaterials,
Germany — 2 Erich Schmid Institute of Materials Science, Austrian
Academy of Sciences, Austria — 3 Ludwig Boltzmann Institute of
Osteology, 4th med. Dept., Hanusch Hospital and UKH Meidling,
Austria — 4 Institute of Materials Science and Testing, Vienna University
of Technology, Austria
Scaffolds made of porous calcium phosphates are potentially interesting
as bone replacement materials. We use a rapid prototyping method based
on microstereolithography and ceramic gelcasting to fabricate highly
porous hydroxylapatite scaffolds suited as substrate for bone cells, whose
strength and stiffness can be adjusted within a certain range. Generally
mechanical properties of cellular solids depend on the apparent density,
the architecture and the properties of the dense material. We showed in
compression tests of cellular structures produced by selective laser sintering
that the strength and stiffness as well as the defect tolerance can
be varied independently from each other by a factor of three, just by
changing the architecture. The scaffolds have been investigated in cell
culture experiments, they were found to support the growth of mouse osteoblasts.
The osteoblasts covered the whole external and internal surface
of the scaffold, they were embedded in an extra cellular matrix consisting
of collagen.
AKB 50.58 Fr 10:30 B
The History of Mutation Pattern along the Human Genome
— •Peter Arndt — Max-Planck Institute for Molecular Genetics,
Ihnestr. 73, 14195 Berlin
Long-ranged correlations of base composition along the chromosomes
have been observed in the human genome. Although this so-called human
isochore structure is known for a long time, we still do not know
its origin or functional consequence. Here we utilize the vast amount of
repetitive sequence deposited in the human genome over the past 250
Myr to investigate differences in the regional mutation patterns. Comparing
substitutional patterns in repetitive elements of various ages, we
reconstruct the history of the base-substitutional process in the different
isochores. At around the time of the mammalian radiation, we find an
abrupt 4- to 8-fold increase of the cytosine transition rate in CpG pairs
compared to that of the reptilian ancestor. Further analysis of nucleotide
substitutions in regions with different GC-content reveals that concurrently
the substitutional pattern changed. We conclude that isochores
have been established before the radiation of the eutherian mammals.
AKB 50.59 Fr 10:30 B
Microfabricated label-free biosensors — •Jürgen Fritz — School
of Engineering and Science, International University Bremen
Label-free microfabricated biosensors offer the advantage of real-time
and highly parallel detection of biomolecules. Two recent examples of
label-free silicon biosensors are presented: nanomechanical cantilever sensors
which detect biomolecules by surface stress and electronic field-effect
sensors, which detect biomolecules by their intrinsic charge. We will discuss
applications, advantages, and limits of both sensors for real-time
detection of nucleic acids and proteins.
J. Fritz et al., Translating biomolecular recognition into nanomechanics,
Science 288 (2000) 316.
J. Fritz et al., Electronic detection of DNA by its intrinsic molecular
charge, PNAS 99 (2002) 14142.
AKB 50.60 Fr 10:30 B
The emergence of a torus-like attractor in a hemin containing
pH oscillator — •Ronny Straube 1 , Dietrich Flockerzi 2 , Marcus
J.B. Hauser 1 , and Stefan C. Müller 1 — 1 Abteilung Biophysik,
Institut für Experimentelle Physik, Otto-von-Guericke Universität, Universitätsplatz
2, D-39106 Magdeburg — 2 Max-Planck-Institut für komplexe
technische Systeme, Sandtorstr. 1, D-39106 Magdeburg
We investigate the bifurcations leading to burst-like oscillations in the
hemin – hydrogen peroxide – sulfite System [1], where hemin can be considered
as a mimick for heme-containing enzymes. For parameter regions
where these kind of oscillations occur, we find an attractor with the topology
of a torus which does not bifurcate locally from a Hopf bifurcation.
Instead it can be described as the union of several quasi stationary manifolds.
The phase flow on the attractor is governed by the dynamics of a
slow variable which triggers the switching between the different parts of
the attractor. Similar behaviour is known from neural systems [2].
[1] R. Straube, S.C. Müller, and M.J.B. Hauser, Z. Phys. Chem. 217,
1427-1442 (2003)
[2] E.M. Izhikevich, Int. J. Bifurcat. Chaos 10, 1171-1266 (2000)
AKB 50.61 Fr 10:30 B
Pressure-Induced Unfolding of Myoglobin: Neutron Diffraction
and Dynamic Scattering Experiments — •Wolfgang Doster 1 ,
Ronald Gebhardt 1 , and Alan Soper 2 — 1 Technische Universität
München, Physik E 13, 85748 Garching — 2 ISIS, Rutherford Appleton
National Laboratory, England
Pressure, as opposed to temperature, probes the role of volume fluctuations
in biophysical reactions without affecting the thermal energy.
This feature can provide new insight into the folding problem. Globular
proteins tend to unfold in response to the application of hydrostatic
pressure typically exceeding 3 kbar. Unfolding is driven by a volume de-