Density gradient centrifugation is a technique that allows the separation of cells, organelles and macromolecules, depending on their size, shape and density.

A density gradient is created in a centrifuge tube by layering solutions of varying densities with the dense end at the bottom of the tube. Cells and large molecules are usually separated on a shallow gradient of sucrose or other inert carbohydrates even at relatively low centrifugation speeds, while macromolecules such as proteins and nucleic acids are separated at higher centrifugation using ultracentrifuges.

When mixtures of cellular extracts are layered on top of a density gradient in a tube and subjected to centrifugation, the various components move through the gradient at different rates that are dependant on their sizes and shapes. These different components appear as distinct bands or zones in the gradient with large components migrating farthest in the tube in...