A-LEVEL BIOLOGY AQA NOTES 
alteration of the sequence of bases in dna can alter the structure of proteins

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Mutations
  • Gene mutations are changes to the base sequence or quantity of DNA within a gene or section of DNA.
  • Gene mutations occur spontaneously during the process of DNA replication.
  • The mutation rate is increased by mutagenic agents, which are chemical, physical or biological agent that causes mutations e.g. UV light
Type of Mutation
Description
​Addition
​Addition of one or more nucleotides
​Deletion
​Removal of one or more nucleotides
​Substitution
​A nucleotide is replaced by a different nucleotide
​Inversion
​A sequence of bases is separated and then reattached in the inverse order
Duplication
​One or multiple bases are repeated
​Translocation
A piece of DNA breaks off and doesn't reattach to itself or its homologous pair.
  • Some mutations may only affect a single codon, changing a single amino acid in a protein, therefore the protein may remain functional. Other may have no effect on protein structure due to the genetic code being degenerate.
  • Mutations such as insertions and deletions can cause frame shifts, changing all the codons and amino acids downstream from the mutation. This results in a unfunctional protein.