Mutations

• Mutations

  • Essential cell maintain DNA structure + prevents damage in replication
  • Cause incorrect or non-functional protein production
  • Mutations happen ~50,000-500,000 daily
  • DNA polymerase proofread DNA copies
  • Ensure base-pairing errors correct immediately
  • Most errors recognised + repaired
  • Some survive
  • Some small; affect nucleotide base DNA sequence
  • Some large; affect large DNA section or whole chromosomes
  • DNA stable, mutations natural + spontaneous
  • Mitosis mutations less serious somatic mutations than meiosis
  • Risk increase by mutagens (e.g. x-rays, cigarettes + caffeine)
• Mutation types

  • 2 types:
  • Substitution (1 base replaces other)
  • Insertion/deletion (1 or more nucleotides inserted or deleted)
  • Affect DNA base sequence, may affect amino acids
  • Often affects 3D structure
  • 3 substitutions:
  • Silent: Affected triplet codes for same AA (degeneracy)
  • Missense: Affected triplet codes for different AA
  • Nonsense: Affected triplet becomes stop codon (truncated protein)
  • Insertion/Deletion:
  • Far worse
  • Cause frameshift
  • Affect later AAs

  Mutation effects

  • Normal: Phenotype unchanged
  • Harmful: Not synthesised/functional
  • Beneficial: New useful characteristic