gene 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
• Normal hemoglobin vs mutated hemoglobin

  • Original DNA sequence: CTT

  Mutated DNA sequence: CTG (G mutation, thymine changed to adenine)
• Mutation impact


  Changes the amino acid sequence 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 that interfere with DNA structure or transcription, e.g. 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 (can be 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 in the subsequent triplets
• Substitution mutation


  One DNA nucleotide is swapped for another, may or may not change the coded amino acid (silent mutation)
• Inversion mutation


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


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