Mutations

• Three types of substitution mutations:

  • Silent - Affected triplet codes for same amino acid (benefit of degeneracy)
  • Missense - Affected triplet codes for different amino acid
  • Nonsense - Affected triplet becomes a stop codon (truncated abnormal protein)
• Insertion and Deletion Mutations: Far worse as they cause a frameshift, and affect all subsequent amino acids; including start/stop codons
• Mutation effects

  • Normal: Functioning proteins still synthesised; phenotype is unchanged
  • Harmful: Proteins not synthesised/non-functional; phenotype negatively impacted
  • Beneficial: Protein synthesised with new/useful characteristics in phenotype
• Essential a cell maintains DNA structure and prevents damage in replication, leading to incorrect or non-functional proteins being produced
• Mutations happen about 50,000 to 500,000 a day, DNA polymerase proofreads DNA copies that it makes, to ensure most base-pairing errors are corrected immediately
• Some errors do occur, but most are recognised and repaired and they do occasionally survive (mutation: random change to genetic material of a cell or organism)
• Some mutations are small and affect nucleotide base sequence on DNA, and some are large and affect large DNA sections or even whole chromosomes
• Although DNA is stable, mutations may occur spontaneously during DNA replication before cell division; mitosis mutations are less serious somatic mutations than in meiosis
• Mutations can occur naturally but their risk can be increased by mutagens (e.g. x-rays, radioactivity, cigarette, caffeine, UV light)
• Two types: Pont or substitution mutation (one base replaces another) and insertion or deletion mutation (one or more nucleotides are inserted or deleted from DNA)
• It affects DNA base sequence, may affect amino acid sequence in protein gene codes for and often affects 3D protein structure and therefore is a function