Gene mutations

• What is a gene mutation?

  A change to one or more nucleotide bases in DNA
• When do most gene mutations take place?

  Most gene mutations happen spontaneously during the process of DNA replication
• What are mutagens?

  Factors that increase the rate of mutations such as uv and ionising radiation, chemicals and viruses
• Why might a mutation not lead to a change in the amino acid sequence?

  • The genetic code is degenerate so a mutation may end up coding for the same amino acid as the original triplet
  • the mutation may occur in an intron
• What is a substitution mutation?

  When a nucleotide is replaced with another nucleotide.
• What could a base substitution result in?

  • A different amino acid and therefore a different amino acid sequence
  • Or the same amino acid and therefore the same sequence
• Why is the amino acid sequence coded for by mRNA important?

  Because it is important in forming the bonds that determine the tertiary structure of the protein. If a mutation occurs which results in a different amino acid being coded for, the amino acid sequence changes and the formation of bonds can be affected. This means that the protein may be a different shape and not function properly.
• Give an example of why the specific shape of proteins is important in biology.

  Enzymes: the shape of the active site has to be complementary to the shape of the substrate molecule for the enzyme to be functional.
• What is a deletion mutation?

  When a nucleotide is lost from the normal DNA sequence
• Why is a deletion mutation more likely to be harmful?

  Because, due to triplet code, it leads to a frame shift resulting in a completely different sequence of amino acids. This means the protein is unlikely to function correctly
• Why might a mutation lead to a non-functional protein?

  • There would be a change in the DNA base sequence
  • This causes a change in the mRNA base sequence
  • Which causes a change in the amino acid sequence
  • This causes a change in the tertiary structure of the protein
  • Which effects the hydrogen/ionic/disulphide bonds of the protein
• Why might a mutation lead to a non-functional enzyme?

  • Mutation causes a change in the DNA base sequence
  • Which causes a change in the mRNA base sequence
  • Which causes a change in the amino acid sequence
  • Which causes a change in the tertiary structure of the protein
  • Which affects the hydrogen/ionic/disulphide bonds in the protein
  • this causes a change in the active site of the enzyme
  • Means that the substrate is no longer complementary
  • So no enzyme-substrate complexes can form
• What is frame shift?

  When the entire sequence after a mutation is shifted either to the left or the right
• What are the two types of gene mutations?

  • Deletion
  • Substitution