R02.3: Chromosome Packaging

Heavily based on Annunziato, A. (2008) DNA Packaging: Nucleosomes and Chromatin. Nature Education 1(1):26

Each nucleated human cells contains about 2 m of DNA - if laid end to end and uncoiled. This is obviously not functional, so the DNA molecule is folded or 'packaged' in the cell.

The primary method of packaging is by histone molecules, a group of positively charged proteins that binds DNA into small beads. These beads are then coiled together to form larger and larger strands, up to the size of a chromosome.

DNA can not be easily read when bound to histones; one method of increasing DNA transcription is to acetylise histone molecules, reducing their binding capacity for the DNA molecule and allowing more transcription to take place. Many malignancies exploit the acetylation of histone molecules to enhance their growth.