Hydrodynamic Shear Breakage of Native DNA

Year: 1971 DOI: 10.7907/5f4m-ns78 Shear breakage is the process by which high molecular weight polymers are broken one or more times by shear stress generated in liquid velocity gradients. This thesis is a kinetic study of the breakage of native DNA from the coliphage λb₂b₅c (contour length 12.8 µ) in dilute aqueous solution. Breakage of this DNA is produced by flow through a capillary. In all our experiments, each DNA molecule breaks only once to form two approximately half-sized molecules. The shear stress required to induce breakage is about 10³ dynes/cm². We find that the kinetics of breakage are first order and that the first order rate constant is a function of the fifteenth power of the shear gradient at 25°C. The shear stress required to produce breakage at a particular rate increases linearly with DNA concentration over the range 0.05 µg DNA/ml to 7.5 µg DNA/ml. We observe a very large temperature coefficient for the breakage rate which arises from the effect of temperature on the viscosity of the DNA solution. This result indicates that the rate limiting step for DNA shear breakage is the speed at which random coil DNA unfolds to an extended configuration when it enters the capillary's liquid velocity gradient. We discuss a kinetic model and a simple theoretical model which have properties similar to those observed experimentally.