Three‐dimensional probe reconstruction for atomic force microscopy

Colloidal gold particles are used as hard, spherical imaging targets to assist in the three‐dimensional reconstruction of the atomic force probe apex. Probe reconstructions are shown to be accurate to 1 nm resolution and dynamically change as the sample is scanned, emphasizing the utility of colloidal gold particles as in situ calibration standards for image reconstruction of a coadsorbed specimen

Scanning Force Microscopy of Chromatin

Scanning force microscopy (SFM) is a new method to obtain the topography of surfaces with nanometer-resolution. The ability to image under liquids makes the technique attractive for biological applications, especially for the determination of the ultrastructure of biomolecules under native conditions. One growing field of interest is the investigation of chromatin and chromatin-related structures. Different levels of chromatin condensation were the subject of several previous SFM investigations, from the nucleosomal chain, to the 30-nm fiber, ending with the metaphase chromosome. The SFM yielded new information on such fundamental problems as the core spacing of the nucleosomal chain, the internal structure of the 30-nm fiber and the banding mechanism of metaphase chromosomes. Other investigations dealt with the SFM characterization of polytene chromosomes. This paper reviews the state-of-the-art in SFM chromatin research and discusses future developments in this field

Microdissection and Measurement of Polytene Chromosomes Using the Atomic Force Microscope

A method to isolate specific regions of the Drosophila polytene chromosome using an atomic force microscope (AFM) was explored. The AFM was used for the microdissection of the locus of interest with much greater precision than standard microdissection techniques. The amplification of DNA isolated in this fashion by the polymerase chain reaction (PCR) is discussed. A study of the effect of hydration level on gross chromosome structure was carried out. It was shown that chromosome swelling is dependent upon humidity or the buffered medium. The significance of this swelling with respect to studies of chromosome structure under physiological conditions is considered

Visualization of circular DNA molecules labeled with colloidal gold spheres using atomic force microscopy

We have imaged gold‐labeled DNA molecules with the atomic force microscope(AFM). Circular plasmid DNA was labeled at internal positions by nick‐translation using biotinylated dUTP. For visualization, the biotinylated DNA was linked to streptavidin‐coated colloidal gold spheres (nominally 5 nm diam) prior to AFM imaging. Reproducible images of the labeled DNA were obtained both in dry air and under propanol. Height measurements of the DNA and colloidal gold made under both conditions are presented. The stability of the DNA‐streptavidin colloidal gold complexes observed even under propanol suggests that this labeling procedure could be exploited to map regions of interest in chromosomal DNA

Analyzing Chromosomes, Ion Channels and Novel Nucleic Acid Structures by AFM

The atomic force microscope (AFM) is proving to be a powerful tool for analysis of biological samples. We provide three examples of the application of AFM to the study of biological questions. First, polytene chromosomes from Drosophila are imaged and manipulated by the AFM. Second, the localization of calcium channels on the release face of a nerve terminal is described. Finally, analyses of a new form of DNA, the G-wire, is presented. These examples illustrate the wide variety of biological questions to which AFM can contribute

Imaging Biological Samples with the Atomic-Force Microscope

The application of atomic force microscopy (AFM) to biological investigation is attractive for a number of reasons. Foremost among these is the ability of the AFM to image samples, even living cells, under near native conditions and at resolution equal to, or exceeding, that possible by the best light microscopes. Moreover, the ability of the AFM to manipulate samples it images provides a novel and far reaching application of this technology

Exploring Conservation of Momentum in Inelastic and Elastic Collisions and Explosions

A GeoGebra applet was created to supplement lectures and experiments surrounding collisions for AP or introductory college physics. Students can explore two-body one-dimensional conservation of momentum problems in this simulation by manipulating the masses and velocities of two colliding objects. They can compare both vectoral and graphical momentum representations of inelastic and elastic collisions as well as the novel addition of explosions, a special form of inelastic collision. In the following article the importance of momentum representation as a graphical area is explained along with the mathematics of the program, hints for using the applet and how it can be incorporated into the classroom