Eukaryotic DNA (AQA A Level Biology): Revision Note

Chromosome structure

• In the nucleus of eukaryotic cells, DNA molecules are very long, linear

• Together, a DNA molecule and its associated proteins form a chromosome

  • The main proteins present are the large, positively charged globular proteins called histones. Their role is to organise and condense the DNA tightly so that it fits into the nucleus

  • The other proteins are enzymes used in copying and repairing the DNA

• The tightly coiled combination of DNA and proteins is called chromatin – this is what chromatids, and therefore chromosomes, are made of

• Chromatids are organised into sections, which is a series of genes

• The ends of the chromatids in chromosomes are ‘sealed’ with protective structures called telomeres