Teuta PiližotaClarendon Laboratory, Department of Physics, University of Oxford, UK

Kolokvij Hrvatskog biofizičkog društva

SINGLE MOLECULE STUDIES OF ROTARY MOLECULAR MOTORS USING AN OPTICAL TRAP WITH FAST PROGRAMMABLE FEEDBACKOptical trapping is a technique that has facilitated much of the progress made in the study of the biophysics of molecular motors at the level of single molecules. A 3-D optical trap can be used to push single motors around, via “handles” such as micron-sized polystyrene spheres. It can also be used to measure the position of such handles with nanometre resolution. To this end we developed an optical trap with back-focal plane detection and fast programmable feedback. A helium-neon laser (632 nm) is used for position detection and a solid-state fibre laser (1064 nm, 3W  CW) forms the trap. Acousto-optic deflectors (AODs) controlled by a digital signal processing board are used to achieve programmable feedback loops with flexible control options and speeds up to 8 kHz.
The system is designed for studies of two rotary molecular motors: the bacterial flagellar motor and the F1Fo-ATPase. The flagellar motor of bacteria is ~50nm in diameter. It is located in the cell membrane and enables the cell to swim by coupling ion-flow across the membrane through the MotA and MotB stator proteins to rotation of the FliF, FliG, FliM and FliN rotor proteins. The motor can rotate in both clockwise and counter-clockwise directions. Recently sub-steps in rotation have been observed. Rotation of the motor drives a helical filament via a universally-jointed hook, providing a propulsive force for bacterial cells to swim. The bacterial flagellar motor is extremely efficient and powerful, and can drive the filament to rotate at speeds of up to 1700 Hz.
utorak, 25. listopada 2005. s početkom u 15:00 sati u predavaonici I krila Instituta Ruđer Bošković, Bijenička c. 54, Zagreb
Prof. Dražen PrelecSloan School, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Kolokvij Instituta Ruđer Bošković i Hrvatskog biofizičkog društva

Subjective judgment, from expert and lay sources, is a part of all human knowledge. Surveys of behaviors, attitudes, and intentions are standard in political science, psychology and economics; subjective expert judgment controls environmental risk analysis, public policy, economic forecasts, scientific hypotheses, military doctrine, artistic and legal interpretations. Although essential for science and policy, subjective judgment is also problematic, because it is hard to know if experts’ judgments are truthful – stated without deception or self-deception – and whether what the experts are saying is true. Hence, there is both a problem of truthfulness and of truth.
I present a scoring method for collecting subjective data (forecasts, estimates) from experts, designed for situations where objective truth is intrinsically or practically unknowable. In this situation, the opinions of other experts provide the only index of judgmental quality. The method assigns high scores, not to the most common answers, but to answers that are ‘more common than collectively predicted,’ with predictions drawn from the same group that generates the answers. This simple adjustment in the scoring criterion removes any potential bias in favor of the ‘average opinion.’ Truthful answers maximize expected score even for an expert – a ‘Cassandra’ – who is sure that her judgment represents a minority view.
srijeda, 4. svibnja u 16:00 sati, predavaonica III krila, Institut Ruđer Bošković, Bijenička c. 54, Zagreb
Prof. dr. Vito TurkDepartment of Biochemistry and Molecular Biology, J. Stefan Institute, Ljubljana, Slovenia

Kolokvij Instituta Ruđer Bošković

Papain-like cysteine proteases are processive and digestive enzymes. Failure in biological control mechanisms causes a wide range of diseases, including several genetic disorders. Most of these enzymes are endopeptidases, although some exhibit an exopeptidase activity. There are 11 human enzymes known and among them 9 with known crystal structures. The enzyme activities are regulated by their propeptides and/or protein inhibitors cystatins and thyropins. Recent findings confirm the role of lysosomal cathepsins in two important mechanisms, antigen processing and apoptosis. Namely, a) the important role of cathepsins S and L in antigen processing via MHC-class II molecules was found and b) there is increasing evidence that lysosomal cathepsins are actively involved in apoptosis by the cleavage of a proapoptotic Bcl-2 family member Bid. In conclusion, cathepsins represent a challenge for further investigations, including drug-design.
petak, 4. veljače u 11:00 sati, predavaonica III krila, Institut Ruđer Bošković, Bijenička c. 54, Zagreb
dr. Selma SupekFizički odsjek, Prirodoslovno-matematički fakultet,  Zagreb ZAŠTO NAS BIOMAGNETIZAM ZANIMA VEĆ 40 GODINA?Izvještaj o sudjelovanju na 14th International Conference on Biomagnetism, Boston, 8-12. kolovoza 2004.

Cjelovitu prezentaciju u .pdf formatu možete preuzeti s ovih stranica putem linka: biomagnetizam – prezentacija (veličina: cca 9MB).

utorak, 25. siječnja 2005. u 14 sati, predavaonica I krila Instituta Ruđer Bošković, Bijenička c. 54, Zagreb
Saša SvetinaInstitute of Biophysics, Faculty of Medicine, University of Ljubljana and J. Stefan Institute, Ljubljana, Slovenia

Kolokvij Instituta Ruđer Bošković

PHYSICS AND BIOPHYSICS OF LIPID VESICLESVesicles are physico-chemical objects characterized by a closed boundary that separates their aqueous inside from their aqueous outside. Typical but not unique vesicle boundaries are lipid membranes. During the last few decades, different classes of vesicle shapes have been revealed both experimentally and theoretically. In this presentation it will first be shown which aspects of vesicle shape behavior are independent and which depend on the material properties of vesicle membranes. The second part of the talk will be devoted to the mechanism of the formation of narrow membrane tubes, to the usage of such tubes for the determination of membrane material constants, and to the role of membrane tubes in different cellular processes. Finally, it will be shown that in a population of growing vesicles, vesicle self-reproduction can occur efficiently only for vesicles in which their growth rate is properly related to certain properties of their membranes. The hypothesis will be put forward about a possible role of vesicles in prebiotic evolution that was derived on the basis of their abilities to compartmentalize, to self-replicate in the indicated selective manner, and to increase the complexity of the system by the way of vesicle fusion. četvrtak, 13. siječnja 2005. u 16:00 sati, predavaonica III krila, Institut Ruđer Bošković, Bijenička c. 54, Zagreb