Practice question

CsCl (cesium chloride) density gradient centrifugation separates macromolecules by isopycnic banding. Upon prolonged high-speed ultracentrifugation, CsCl forms continuous gradient of increasing density. In presence of ethidium bromide, supercoiled plasmid, linear chromosomal DNA, and RNA achieve equilibrium where their buoyant density equals surrounding CsCl solution. Supercoiled plasmid binds less EtBr and retains higher buoyant density than nicked or linear DNA. Separation is therefore based purely on buoyant density differences, not viscosity, UV absorption, or solubility, allowing isolation of supercoiled plasmid fraction with high purity.