A-Level Biology AQA Notes
3.8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins
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.