Mutations

• Gene mutation


  Alteration of a base sequence in DNA
• Gene mutations are likely to occur when DNA is replicating, which happens in interphase of the cell cycle
• Mutation impact


  Changes the amino acid sequence (primary structure) in the polypeptide chain, altering the 3D shape and function of the protein
• Mutagenic agents


  • High energy ionizing radiation (alpha, beta, X-rays, gamma rays)

  Carcinogens (chemicals like tobacco smoke, mustard gas, peroxides)
• Exposure to mutagenic agents increases the risk of spontaneous mutations, but does not guarantee a mutation will occur
• Types of gene mutations

  • Addition (frame shift)

  Deletion (frame shift)

  Substitution (sometimes silent)

  Inversion

  Translocation
• Addition mutation


  One DNA nucleotide is accidentally added, causing a frame shift in the subsequent triplets
• Deletion mutation


  One DNA nucleotide is deleted, causing a frame shift (to the left) in the subsequent triplets
• Substitution mutation


  One DNA nucleotide is swapped for another, sometimes resulting in a different amino acid but sometimes a silent mutation
• Inversion mutation


  A section of DNA detaches and rejoins in the reverse orientation
• Translocation mutation


  A section of DNA breaks off one chromosome and attaches to a different chromosome