Understanding:
• Nucleosomes help to supercoil the DNA
In eukaryotic organisms, the DNA is packaged with histone proteins to create a compacted structure called a nucleosome
- Nucleosomes help to supercoil the DNA, resulting in a greatly compacted structure that allows for more efficient storage
- Supercoiling helps to protect the DNA from damage and also allows chromosomes to be mobile during mitosis and meiosis
Organisation of Eukaryotic DNA
- The DNA is complexed with eight histone proteins (an octamer) to form a complex called a nucleosome
- Nucleosomes are linked by an additional histone protein (H1 histone) to form a string of chromatosomes
- These then coil to form a solenoid structure (~6 chromatosomes per turn) which is condensed to form a 30 nm fibre
- These fibres then form loops, which are compressed and folded around a protein scaffold to form chromatin
- Chromatin will then supercoil during cell division to form chromosomes that are visible (when stained) under microscope
Understanding:
• Utilisation of molecular visualisation software to analyse the association between protein and DNA
within the nucleosome
A nucleosome consists of a molecule of DNA wrapped around a core of eight histone proteins (an octamer)
- The negatively charged DNA associates with positively charged amino acids on the surface of the histone proteins
- The histone proteins have N-terminal tails which extrude outwards from the nucleosome
- During chromosomal condensation, tails from adjacent histone octamers link up and draw the nucleosomes closer together
To view the structure of a nucleosome via an interactive pop-up, click on the name of the structure below:
