BIO 002 MUTATION

Page 1: Hfr Cells and Bacterial Conjugation

• Hfr Cells:

  • Formation of Hfr cells involves the integration of the F element with the main bacterial chromosome.

  • Allows for transfer of chromosomal DNA via a conjugation tube.

  • An Hfr cell has high frequency of conjugation.

  • Insertion process: Circular F element breaks, forming a linear segment of the chromosome.

  • A strand of the chromosome is pulled into the recipient (F-) cell and copied.

Page 2: Nature and Classification of Mutation

• Definition of Mutation: Change in the nucleotide sequence of DNA in an organism.

  • Mutant Strain: Expresses the mutation.

  • Wild Type Strain: Does not express the mutation.

• Classification of Mutation:

  • Heredetary Mutation:

    • Inherited from parents, present in almost every cell, especially germ cells.

  • Acquired/Somatic Mutation:

    • Occurs during life, present in certain cells only, not heritable.

    • Can arise from environmental factors or errors in cell division.

  • Types of Mutations:

    • Spontaneous Mutations: Arise naturally without any added agents.

    • Induced Mutations: Result from exposure to mutagens (physical/chemical agents).

Page 3: Types of Spontaneous Mutation

• Common Expression:

  • Base substitution is the primary form.

  • Types of Base Substitution:

    1. Point Mutation: Replacement of one nucleotide with another.

       • Missense Mutation: Changes one amino acid in a protein (e.g., Adenine to Cytosine results in Proline).

       • Silent Mutation: Changes nucleotide but does not alter amino acid produced.

    2. Frame Shift Mutation: Involves insertion or deletion of nucleotides, altering protein coding drastically.

Page 4: Frame Shift and Mutagens

• Frame Shift Mutation: Insertion or deletion that causes changes in the reading frame.

• Mutagens:

  • Substances causing mutations, categorized as:

    1. Chemical Mutagens: Affect DNA structure.

    2. Physical Mutagens: e.g., radiation (UV, X-rays).

Page 5: Chemical Mutagens

• Types of Chemical Mutagens:

  1. DNA-Reactive Chemicals: React chemically with DNA, causing mutations.

     • Example: Nitrous acid removes amino groups from purines/pyrimidines.

  2. Base Analogs: Similar to regular bases, but disrupt hydrogen bonding (e.g., 5-bromouracil mimics thymine).

  3. Specific Mispairing: Alters base pairing (e.g., Methyl mitrosogunidine adds methyl groups to guanine).

  4. Intercalating Agents: Insert themselves between DNA bases, causing distortion.

Page 6: Physical Mutagens

• Types of Physical Mutagens:

  1. Ionizing Radiation: X-rays and gamma rays leading to DNA breakage.

  2. Non-Ionizing Radiation (e.g., UV): Causes dimer formation and can distort DNA replication.

Page 7: Biological Mutagens

• Biological Agents:

  1. Transposable Elements: Move within the DNA and cause mutations (transposon mutagenesis).

  2. Insertion Sequences: Short sequences that lead to mutations.

  3. Mu Phage: Acts as a transposable element, inducing mutations by its movement.