Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Dienstag
AKB 20 Physics of DNA
Zeit: Dienstag 09:30–11:00 Raum: H40
Hauptvortrag AKB 20.1 Di 09:30 H40
Physics of DNA Compaction into Chromatin — •Helmut
Schiessel — Max-Planck-Institute for Polymer Research, Theory
Group, D 55021 Mainz
Chromatin is the dense complex between DNA and histone proteins
that occupies the nuclei of plant and animal cells. At the lowest level the
DNA is wrapped around protein spools forming so-called nucleosomes.
The resulting string of nucleosomes is folded into the chromatin fiber. I
will present theoretical models that allow to interpret recent experiments
on the stretching of single nucleosomes and of chromatin fibers.
Our findings on single nucleosomes suggest a mechanism by which the
nucleosome combines two seemingly contradictory features: being very
stable and having its wrapped DNA highly accessible at the same time.
Our results on fiber stretching show the delicate interplay between soft
elasticity due to the DNA linker backbone and stiffening due to internucleosomal
contacts – directing the folding of fibers at the next level of
DNA compaction.
cf. also the review: H. Schiessel, J. Phys.: Condens. Matter 15 (2003)
R699-R774
AKB 21 Bioadhesion and Molecular Forces
Hauptvortrag AKB 20.2 Di 10:00 H40
Structure and Dynamics of DNA Nanoparticles — •Joachim
Rädler — Geschwister-Scholl-Platz 1, D-80539 München
e report on various strategies to assemble cationic lipid-DNA and
polypeptide DNA nanocomplexes. For application in gene therapy wellcontrolled
single- plasmid particles are formed from dilute solutions of
DNA and oppositely charged macromolecules. The internal structure,
size and transport properties of the complexes are characterized using
small angle X-ray scattering, fluorescence microscopy and fluorescence
correlation spectroscopy.
Hauptvortrag AKB 20.3 Di 10:30 H40
Electronic Detection of DNA on Transistor Arrays — •Ulrich
Bockelmann, François Pouthas, Cedric Gentil, and Denis
Cote — LPMC Ecole Normale Supérieure, Paris, France
This talk will focus on our research on electronic detection of unlabeled
biomolecules. Field effect measurements, based on integrated silicon transistor
arrays, are used to detect DNA bound to a solid/liquid interface.
The planar configuration is compatible with DNA chip technology and
with microfluidics approaches.
Zeit: Dienstag 11:30–13:00 Raum: H40
Hauptvortrag AKB 21.1 Di 11:30 H40
Chemische Kinetik einzelner spezifischer Bindungen — •Rudolf
Merkel 1 und Melanie Nguyen-Duong 2 — 1 Institut für Schichten
und Grenzflächen, Forschungszentrum Jülich — 2 Lehrstuhl für Biophysik
E22 der Technischen Universität München
Bioadhäsion ist ein physiologischer Prozess von großer Bedeutung. Der
zugrunde liegende Mechanismus ist die spezifische Erkennung und Bindung
zwischen komplementären Zelladhäsionsmolekülen, welche biologische
Strukturen (z.B. zwei Zellen) mechanisch verbinden. Erst in den
letzten Jahren wurden mechanische Experimente an einzelnen solchen
Bindungen möglich. Hierbei zeigte sich überraschenderweise, dass die Dissoziationsrate
einzelner Bindungen, welche mikroskopische Körper verbinden,
ungefähr 100 mal größer ist im Vergleich zu Bindungen zwischen
denselben Molekülen in Lösung. Wir präsentieren hier eine mögliche Erklärung
dieses Phänomens sowie entsprechende experimentelle Befunde.
Hauptvortrag AKB 21.2 Di 12:00 H40
Forces acting on Biological Model Systems — •Udo Seifert — II.
Institut für Theoretische Physik, Universität Stuttgart, 70550 Stuttgart
An overview on our recent theoretical work about the effects of forces
on three biological model systems will be given. (i) Forces acting on adhering
vesicles lead to significant shape changes thereby inducing detachment
of bound vesicles either by smooth deformations for weak adhesion
or tether formation for strong adhesion [1]. (ii) Time-dependent forces
AKB 22 Single Molecule Methods
acting on surfaces hold together by receptor/ligand pairs lead to rupture
depending on the loading rate. For slow loading rebinding events
become crucial [2]. (iii) For forces acting on a single biopolymer with two
equilibrium configurations (like folded/ unfolded) the equilibrium energy
landscape along the pulling co-ordinate can be reconstructed even from
non-equilibrium experiment data by using the Jarzynksi relation.
[1] A. Smith, E. Sackmann and U. Seifert, Europhys. Lett. 64, 281,
2003.
[2] U. Seifert, Phys. Rev. Lett. 84, 2750, 2000; Europhys. Lett. 58, 792,
2002.
[3] O. Braun, A. Hanke and U. Seifert, in preparation.
Hauptvortrag AKB 21.3 Di 12:30 H40
Cell Organization in Soft Media due to Active Mechanosensing
— •Ulrich Schwarz — Max Planck Institute of Colloids and Interfaces,
Golm
Adhering cells actively probe the mechanical properties of their environment
in order to position and orient themselves. In an elastically
anisotropic environment, cells prefer to orient in the direction of maximal
effective stiffness. By converting this observation into an extremum
principle in linear elasticity theory, we can predict cell organization in
soft media in excellent agreement with experiments with fibroblasts on
elastic substrates and in hydrogels. We also discuss how effective cell behaviour
might follow from the stochastic dynamics of cell-matrix contacts
under force.
Zeit: Dienstag 14:00–16:00 Raum: H40
Hauptvortrag AKB 22.1 Di 14:00 H40
A Biophysical View of Molecular Recognition — •Dario Anselmetti
—
Mechanical unbinding experiments with single molecules give insights
into the physico-chemical fundamentals and mechanisms of biomolecular
recognition and specific interaction. In biology, this is often associated
with complex processes such as replication, transcription/translation, or
gene regulation. After an introduction, which briefly explains our experimental
methods (single molecule force spectroscopy with AFM and
optical tweezers), key findings between mechanical single-molecule experiments
and biomolecular ensemble experiments are summarized. Latest
results on transcriptional proteins and DNA, synthetically produced
peptide analoga and DNA, as well as on artificial recognition elements
(supramolecular guest-host systems) will be presented and discussed
within the framework of our Nanobiology activities.
Hauptvortrag AKB 22.2 Di 14:30 H40
Mechanical Single Molecule Experiments in the Thermal Energy
Regime — •Ernst-Ludwig Florin — EMBL, Cell Biology and
Biophysics Programme, Meyerhofstrasse 1, D-69117 Heidelberg
Hauptvortrag AKB 22.3 Di 15:00 H40
Labeling of Cells with Quantum Dots — •Wolfgang Parak —
Center for Nanoscience, LMU Muenchen, Muenchen, Germany
Colloidal quantum dots are semiconductor nanocrystals well dispersed
in a solvent. The optical properties of quantum dots, in particular the