Unhooking dynamics of U-shaped DNA molecule undergoing gel electrophoresis

It has been found that DNA molecules are often hooked around obstacles in a U-shaped configuration in gel electrophoresis. To understand the dynamics of the unhooking of U-shaped DNA molecules undergoing gel electrophoresis, we have examined the length changes of the longer and shorter arms of the U-shape as a function of time. Two types of unhooking have been found. In one type, the length changes of both arms are expontential in time but with different time constants. In another type, the length changes of the shorter arm is exponential and that of the longer one is linear with time. The interpretation is that the extent of stretch of the spring-like DNA chain decreases as the length difference between the two arms increases during the unhooking processes, and that the frictions at the pivot point can be relatively large depending upon the local structure of the gel. The friction coefficient at the pivot point is estimated to be nu 0 = (2.98 +/- 1.42)x10(-5) g/sec.