DNA and the Structure of Proteins

• What is a mutation?

  An alteration to the DNA base sequence. Mutations 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 (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 a significant impact, and why?

  Insertion, deletion, duplication and translocation. These mutations produce a frameshift, meaning the entire amino acid sequence produced will be different.
• Which mutations are less likely to have a significant impact, and why?

  Substitution and inversion. These mutations only alter one or very few triplets, the amino acid sequence might not be affected due to the degenerate nature of the genetic code.
• Are mutations always harmful?

  No; may be neutral/silent if the resulting change in the protein has no effect on the organism. Also may be beneficial, basis for evolution and natural selection.
• What is a mutagenic agent, and 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