The first step
in many protein studies is to separate cellular parts first,
so that you can study
the proteins in specific parts of the cell, such as proteins
in the nucleus, for example.
One popular approach is to centrifuge cells at high speeds. This is like those rides in amusement parks
that spin you around and around in a horizontal plane. To get the best separation
of cell parts, you must use
very expensive centrifuges that spin at enormous speeds. This separates
the components of the cells according to their weight. For example,
chromosomes are heavy, so they would be slung down toward the bottom
of the tube. Lighter weight organelles would be located toward the top.
Centrifugation works best
if cells are broken up and put in a liquid that can suspend the cell
parts in different layers. A gradient of different organelles of concentrations is a very popular solvent system for separating different
parts of a cell (mitochondria spin down in one layer of the solvent,
membranes in another, chromosomes in another, and so on).