Publications

Through direct observation of long deoxyribonucleic acid (DNA) by means of fluorescence microscopy, we investigated the dynamics of individual DNA chains under alternating current electric fields in concentrated polyacrylamide solutions. By the study on the conformational change of the DNA in a wide range of frequencies, we have noticed the existence of four different regions depending on the frequency, as for the dynamic behavior of the DNA; i.e., linear motion, anti-resonance, stretching, and orienting. The four regions are characterized by the time dependence of the maximum length R-l and the position of the center of mass G(x) of the DNA. In the linear motion region, R-l is almost constant, and G(x) changes sinusoidally with time. In the anti-resonance region, both R-l and G(x) change sinusoidally. In the stretching region, both R-l and G(x) are almost constant. In the orienting region, both R-l and G(x) are almost constant, but the DNA is not fully stretched. We observed that long DNA molecules with various lengths, ranging from 16 mu m to over 200 mu m, are elongated in the stretching region, indicating that this stretching phenomenon would be independent of the length of DNA. By the observation of the stretching process, it was found that the asymmetric effect of the electric field is essential for the stretching. We explain such asymmetric effect by using simple tube model.