The cells of our body store genetic information in the cell nucleus. As nuclei are very small and DNA molecules are very long, this is not an easy task. It’s like trying to store a very thin string, 10 kilometers long, in the volume of a pea. DNA must therefore be packaged very tightly to fit into the nucleus. Proteins help to package DNA by forming a structure with DNA called chromatin. Peter analyses a group of enzymes that use chemical energy to keep chromatin flexible so that genetic information can be utilised when needed despite its dense packaging.