MUTATIONS

• WHAT IS A MUTATION?

  random change in the DNA base sequence of an organism
• EFFECTS OF A SUBSTITUTION OF BASES MUTATION?

  NONSENSE

  • substitutes stop codon for AA
  • polypeptide stopped early
  • non-functional protein

  MISSENSE

  • AA substitution
  • different protein structure
  • conservative/ non-conservative

  SILENT

  • same AA
  • no effect on polypeptide
  • degenerate
• OTHER TYPES OF GENE MUTATION?

  ADDITION

  • frameshift

  DELETION

  • frameshift

  DUPLICATION

  • one or more bases are repeated
  • frameshift to right

  INVERSION

  • group of bases separated
  • rejoin in inverse order

  TRANSLOCATION

  • group of bases separated from one chromosome
  • inserted into another
• CAUSES OF MUTATION?

  HIGH ENERGY IONISING RADIATION

  • alpha and beta particles
  • X-rays/ UV light
  • disrupt DNA structure

  CHEMICALS

  • NO2 directly alters DNA structure/ interfere with transcription
  • benzopyrene inactivates tumour-suppressant gene causing cancer
  • mustard gas
• OTHER TYPE OF MUTATION THAT IS NOT A CHANGE TO DNA BASE SEQUENCE?

  NON-DISJUNCTION: homologous chromosomes fail to separate during meiosis 1 so daughter cells have one extra or one less chromosome
• WHAT IS A FRAMESHIFT?

  when all DNA base triplets downstream from mutation are changed
• WHY MAY A FRAMESHIFT NOT OCCUR?

  if bases are altered in multiples of three
• WHY DO SUBSITUTION AND INVERSION MUTATIONS NOT CAUSE A FRAMESHIFT?

  no DNA base triplets downstream from the mutation are changed