L47: Mutagenesis and mutations

• What is the first nucleotide mentioned in the study material?

  Cytosine
• What is the second nucleotide mentioned in the study material?

  Guanine
• What is the third nucleotide mentioned in the study material?

  Adenine
• What is the fourth nucleotide mentioned in the study material?

  Thymine
• What are the types of DNA substitutions mentioned?

  • Transitions
  • Transversions
• What can cause segregation of mismatched base pairs?

  • Error in replication
  • Tautomerization
  • Deamination
• What can be the consequence of point mutations?

  Some mutations are lethal and not inherited
• What can non-coding DNA affect?

  Transcription and regulation of translation
• What percentage of DNA is non-coding in bacteria and archaea?

  6-14%
• What are the types of mutations in the coding sequence?

  • Silent mutations
  • Missense mutations
  • Nonsense mutations
• What is a silent mutation?

  Genotype changed but not phenotype
• What is a missense mutation?

  Genotype changed and phenotype may change
• What is a nonsense mutation?

  Usually detrimental and changes both genotype and phenotype
• What happens during insertions and deletions?

  • Can cause frameshift mutations
  • Affect coding or regulation
• What is a frameshift mutation?

  Caused by insertions or deletions affecting reading frame
• What happens to the protein in a silent mutation?

  Nothing changes in phenotype
• What happens to the protein in a missense mutation?

  Can be detrimental but often nothing changes
• What happens to the protein in a nonsense mutation?

  Usually detrimental and may produce longer proteins
• What are the minimal growth requirements for E. coli strains?

  • Minimal medium with glucose
  • Specific amino acids depending on strain
• What are large scale mutations?

  • Deletions
  • Inversions
  • Tandem repeats
  • Transposons
• What is a deletion mutation?

  Can remove kilobases and lose several genes
• What is an inversion mutation?

  Can flip kilobases and disrupt genes
• What are tandem repeats?

  Part of genome is duplicated
• What are transposons?

  Nucleotide sequences that can move themselves
• What is a reversion mutation?

  Restores the original sequence
• What are suppressor mutations?

  Restore original phenotype through second mutation
• What is intergenic suppression?

  Occurs in a different gene than the first mutation
• What is the role of anticodons?

  Complementary to the codon of the amino acid
• What is nonsense suppression?

  Suppresses premature stop codons
• Why are mutants important in research?

  Essential for understanding biochemistry and cell biology
• What can cause mutations in bacteria?

  Spontaneous or exposure to mutagens
• What is the minimal growth requirement for E. coli gal Δ (ara) lac bio am supF?

  Minimal medium plus glucose at 37°C
• How can we select mutants?

  • Selectable phenotypes: drug resistance
  • Conditional lethal mutants
  • Replica plating
• What is the process to make a histidine auxotroph?

  1. Expose to mutagen
  2. Grow in complex medium
  3. Penicillin enrichment
  4. Plate on minimal medium + histidine
  5. Replica plate to double check
• What is phenotype lag?

  Resistance may not be seen for generations
• What happens to E. coli with a tonB mutation?

  No more TonB protein is made
• What does the protein encoded by the gene tonB do?

  It spans the periplasm and outer membrane
• What happens when there is a mutation to tonB?

  No more TonB protein is made
• How many copies of TonB can be present before mutation?

  Up to 1000 copies
• What happens to E. coli after several generations post-tonB mutation?

  Phenotype is not seen for several generations