Lecture 14_250 review

Exam 2 Review Topics

Lecture 14: Mutations

Wild Type vs Mutant DNA

• Wild Type: The normal, non-mutated version of a gene or organism.

• Mutant DNA: Refers to variations or alterations in the DNA sequence which may result in a different phenotype.

Types of Mutations (DNA Perspective)

• Point Mutation: A change in a single nucleotide which can lead to alterations in the corresponding amino acid.

• Substitution: A type of point mutation where one nucleotide is replaced by another.

• Inversion: A segment of DNA is reversed within the chromosome.

• Insertion: Addition of one or more nucleotides into the DNA sequence.

• Deletion: Removal of one or more nucleotides from the DNA sequence.

• Reversion: A mutation that restores the original phenotype after mutation.

Types of Mutations (Protein Perspective)

• Silent Mutation: No change in the amino acid sequence of a protein; often due to redundancy in the genetic code.

• Missense Mutation: A single amino acid change in a protein, which may alter its function.

• Conditional Mutation: A mutation that exhibits wild-type phenotype under certain conditions but a mutant phenotype under others.

• Nonsense Mutation: A mutation that creates a premature stop codon in the protein sequence, leading to truncated proteins.

• Frame-shift Mutation: Caused by insertion or deletion of nucleotides that shifts the reading frame of the sequence, altering downstream amino acid sequence.

Causes of Mutations

• Induced Mutations: Caused by external factors like chemicals or environmental influences. (e.g. radiation, chemical mutagens)

• Spontaneous Mutations: Naturally occurring changes in DNA that happen without any external influence.

• Mutagens: Agents that cause mutations.

  • Radiation:

    • Ionizing Radiation: High-energy radiation that removes tightly bound electrons from atoms, leading to DNA breaks.

    • Non-Ionizing Radiation: Lower energy radiation (e.g., UV light) that can cause nucleotide bonds to break or distort DNA structure.

DNA Repair Mechanisms

• Proofreading: The process by which DNA polymerase checks and corrects errors in newly synthesized DNA.

• Mismatch Repair: The identification and correction of incorrectly paired nucleotides after DNA synthesis.

• Nucleotide Excision Repair: A repair mechanism that removes damaged sections of DNA and replaces them with the correct sequence.

Ames Test

• Description: A biological assay to assess the mutagenic potential of chemical compounds by observing mutations in bacteria (usually Salmonella).

• Components:

  • Liver Extract: Used to simulate metabolism of compounds in a mammal.

  • hisG Salmonella Mutant: A strain of Salmonella that is deficient in histidine synthesis, requiring histidine to grow.

  • Revertants: Mutants that revert to the wild type phenotype either spontaneously or through exposure to mutagens.

  • Mutagen: Any agent that increases the rate of mutation.

  • Spontaneous vs Induced Mutation: Distinction between mutations that occur naturally versus those induced by external factors.