A-Level Biology AQA Notes

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Genetic Information

In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.
In eukaryotes, the nucleus contains very long, linear DNA molecules associated with proteins, called histones. Together a DNA molecule and its associated proteins form a chromosome.
The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.
The genome is the full set of DNA found in an organism.
The proteasome is the full range of proteins that can be synthesised from the genome.
A gene is a section of DNA that code for polypeptides and functional RNA and are located at a fixed locus on a DNA molecule.
A sequence of three DNA bases, called a codon, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate.
In eukaryotes, sections of the nuclear DNA do not code for polypeptides (introns). Exons are sections of DNA that code for amino acid sequences.

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