Something about
Each of our cells (or more correctly, nearly all of our cells) contains a copy of this genome, encoded in three billion base pairs of DNA.
This information is precious and must be carefully guarded. Inside our cells, a collection of repair enzymes corrects chemical changes inflicted on the strands by environmental insults.
But the delicate strands must also be protected from physical damage. This is the job of nucleosomes
3D model present :
- molecular surface of nucleosom
- double stranded DNA
A Paradox
The job of the nucleosome is paradoxical, requiring it to perform two opposite functions simultaneously. On one hand, nucleosomes must be stable, forming tight, sheltering structures that compact the DNA and keep it from harm. On the other hand, nucleosomes must be labile enough to allow the information in the DNA to be used. Polymerases must be allowed access to the DNA, both to transcribe messenger RNA for building new proteins and to replicate the DNA when the cell divides. The method by which nucleosomes solve these opposed needs is not well understood, but may involve a partial unfolding of the DNA from around the nucleosome, one loop at a time, as the information in the DNA is read.