Lecture 16 - Gene Mutation and DNA Repair

  • Definition of Mutation: Change in DNA sequence affecting protein production.

  • Types of Mutations:

    • Germ-line:

    • Occur in reproductive cells (heritable)

    • Somatic:

    • Occur in non-reproductive cells (non-heritable)

  • Fitness of Mutations:

    • Lethal: Non-viable

    • Harmful: Reduces survival and reproduction

    • Neutral: No phenotypic effect

    • Beneficial: Confers advantages in new environments

  • Categories of Mutations:

    • Substitution: Change in a base (e.g., GGG to GAG)

    • Deletion: Removal of bases (e.g., TTGGGATTT to TGITT)

    • Insertion: Addition of bases (e.g., GAGA to GAGAGA)

    • Inversion: Bases flipped (e.g., TCTC to AGAG)

  • Effects of Mutations on Proteins:

    • Silent Mutation: No amino acid change

    • Missense Mutation: One amino acid change

    • Nonsense Mutation: Creates a stop codon

    • Frameshift Mutation: Alters reading frame due to insertions/deletions

  • Causes of Mutations:

    • Spontaneous: Errors during DNA replication

    • Induced Mutations: From external mutagens

    • Chemical Mutagens: Mimic bases (e.g., 5-bromouracil)

    • Intercalating Agents: Cause frameshifts (e.g., Proflavin)

    • Radiation: DNA damage from UV light

  • Trinucleotide Repeat Expansion:

    • Result from strand slippage

    • Excess repeats lead to disorders (e.g., Huntington's, Fragile X)

  • Consequences of DNA Damage:

    • Can lead to cancer and aging

    • Unrepaired damage prompts DNA repair mechanisms to act.