Eukaryotic DNA (AQA A Level Biology): Revision Note
Exam code: 7402
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


Examiner Tips and Tricks
It is important to distinguish when the terms chromatin, chromatids and chromosomes are used.
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