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
Opposites Attract
The histone proteins are perfectly designed for their jobs, so much so that histones are nearly identical in all non-bacterial organisms. Even slight modifications can be lethal. The surface of the histone octamer, shown on the left, is decorated with positively charged amino acids, shown with bright blue nitrogen atoms. These interact strongly with the negatively-charged phosphate groups on the DNA, shown at the right with bright yellow phosphorous and bright red oxygen atoms. This serves to glue the DNA strand to the protein core. This is no simple task. DNA is normally a long, straight molecule, but in nucleosomes the DNA must be forcibly bent into these two tight circles.