D2.1.6

• DNA wraps around a protein called histone.
• Strands of DNA wrap around histones to form a structure called a nucleosome.
• Nucleosomes fold on top of each other into single chromatin fibres, which are then further coiled and intertwined into a chromosome.
• Packaging the DNA helps it do its jobs so that all the individual strands can be accessed.
• Microtubules are hollow cylinders of tubulin proteins that can be rapidly assembled and disassembled.
• Some of the microtubules are disassembled in the early stages of mitosis and the reassembled by microtubule organising centres (MTOCs).
• Kinetochores are assembled on the centromere of each chromatid.
• Kinetochores act as a microtubule motor by removing tubulin subunits from the attached ends of the microtubules. This shortens the microtubules linking the kinetochores to the poles, putting them under tension.