A-LEVEL NOTES
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A-LEVEL NOTES

A-LEVEL BIOLOGY AQA NOTES 
dna, genes and chromosomes


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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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