gene mutations

• what is a gene mutation?

  when theres a change in dna base sequence
• when is a gene mutation likely to occur?

  when dna is replicating, during interphase
• dna mutations are spontaneous but the frequency may be increased by certain factors called mutagenic agents
• mutations in a base may result to a different amino acid sequence in the polypeptide so when the protein is modified into the tertiary structure it will form hydrogen, ionic and disulfide bonds in different places causing it to fold differently into a different 3d shape producing a non-functioning protein
• name the two mutagenic agents?

  high energy and ionising radiation and carcinogens
• (mutagenic agents) high energy and ionising radiation

  • alpha particles , beta particles , gamma rays and x-rays are ionising
  • ultraviolet light is not ionising but has high energy and can cause damage and disrupt the structure of dna
• (mutagenic agents)- carcinogens

  • chemicals that can alter the structure of dna and interfere with transcription
  • these chemicals include , peroxides , tobacco smoke and mustard gas
• there are 6 gene mutations

  1. addition
  2. deletion
  3. substitution
  4. inversion
  5. duplication
  6. translocation
• addition mutation

  • one extra base is added to the sequence
  • when an extra base is added the subsequent codon is altered which causes a frame shift
  • may produce a non-functioning protien
• deletion mutation

  • deletion of a base in a sequence
  • causes frame shift to the left
  • may form a non-functioning protein
• substitution mutation

  • one base is changed for a different base
  • number of bases remain the same , there is no frame shift
  • only one codon changes
  • due to the genetic code being degenerate it may still code for the same amino acid
• inversion mutation:

  • a section of dna detaches and when they rejoin they are inverted so are front to back
  • results in a different amino acid being coded
• translocation mutation

  • a section of bases on one chromosome detaches and attaches to another chromosome
  • substantial alteration and causes significant impact on gene expression and therefore resulting in a different phenotype
• duplication mutation

  • when a base is duplicated
  • causes frame shift