DNA and the structure of proteins

• What is a mutation?

  An alteration to the DNA base sequence

  Often arise spontaneously during DNA replication
• What are addition and deletion mutations?

  Where one or more nucleotides (bases) are either inserted or deleted from the DNA sequence
• What is a substitution mutation?

  Where one nucleotide (base) in the DNA sequence is replaced by another
• What is a duplication mutation?

  Where one or more nucleotides (bases) duplicate and repeat
• What is an inversion mutation?

  Where a group of nucleotides (bases) become separated from the DNA sequence, then rejoin in the reverse order i.e. they have flipped
• What is a translocation mutation?

  Where a group of nucleotides (bases) become separated from the DNA sequence, and are then inserted into the DNA of a different chromosome
• Which mutations are most likely to have significant impact and why?

  • Insertion, deletion, duplication, translocation
  • Because they produce a frameshift, meaning the entire amino acid sequence produced will be different
• Which mutations are most likely to have a smaller impact and why?

  • Substitution, inversion
  • Because they only alter one or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code
• Is a mutation resulting in a change to the amino acid sequence always harmful?

  • No
  • May be neutral if the resulting change in protein has no effect on the organism
  • Also may be beneficial, which is the basis for evolution and natural selection
• What is a mutagenic agent? Give examples

  Factors that increase the rate of gene mutation

  • Chemical mutagens such as alcohol and benzene
  • Ionising radiation such as UV and x-rays
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