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1 July 1990 Observation of individual DNA molecules responding to changing electric fields
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Individual ethidium stained DNA molecules, 50 kbp to 2Mbp in length, are observed with a fluorescence microscope, image intensifier, and video camera. The microscope slide is equipped with electrodes to . introduce an electric field across the sample. An array of electrodes, controlled by computer, can select both field strength and direction. When embedded in a thin (10-20 micron) layer of agarose and electrophoresis buffer, linear DNA molecules snake through the gel toward the positive electrode. The linear polymers alternately stretch and contract as they become hooked around obstacles and then slip off. Mechanisms responsible for size separation in pulse field gel electrophoresis are explored. Open circular plasmids become permanently trapped on gel obstructions in a strong electric field. They behave like negatively charged rubber bands as they elongate in a strong field and contract as the field is reduced. Measurement of plasmid elongation in various fields allows calculation of the effective electrophoretic charge on DNA. Measurement of random coil diameters permits calculation of DNA's persistence length.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Steven B. Smith "Observation of individual DNA molecules responding to changing electric fields", Proc. SPIE 1206, New Technologies in Cytometry and Molecular Biology, (1 July 1990);

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