tailieunhanh - Atomic Force Microscopy in Cell Biology Episode 2 Part 9

Tham khảo tài liệu 'atomic force microscopy in cell biology episode 2 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 346 Humphris and Miles Fig- 5 A 1 agarose gel under water imaged with an effective quality factor of 300 a and b and with conventional tapping mode c and d . Topography a and c is displayed with a z range of 150 nm and phase contrast b and d with a range of 5 degrees. See Color Plate. 16. Dynamic Force Microscopy and Spectroscopy 347 Fig. 6 A living rat kidney cell imaged in buffer with an effective quality factor of 300 height a z range J m and phase b range 60 . See Color Plate. B. Dynamic Force Spectroscopy 1. Background The measurement of force as a function of extension of a single molecule using AFM force-sensing techniques has been named force spectroscopy. Some of the measurements already reported involved the forces associated with the unfolding of protein structures Lenne et al. 2000 Oesterhelt et al. 2000 Rief et al. 1998 1999 and it is hoped that information on the nature of the folded structure can be extracted from these force measurements. Such molecular processes are dynamic and energetic and exhibit both conservative and dissipative forces. The use of the active-2 technique allows the measurement of the complex meachanical properties of such a process in the appropriate buffer environment Humphris et al. 2000 . The increase in the quality factor to over 300 in liquid facilitates the tracking of the resonant frequency and the separation of conservative and dissipative forces. Tracking the resonant frequency via a phase-locked loop is the approach that has been used here. Such information also allows the measurement of the effective viscosity of a single molecule. The implementation of dynamic force spectroscopy not only increases the sensitivity of the measurement but also decouples the conservative elastic and dissipative viscous components of the force associated with the molecular extension. One realization of the dynamic force spectroscopy experiment is shown in Fig. 8. In the standard method of force spectroscopy a molecule bound at one end