Lecture 8 Flashcards
(6 cards)
Describe the Luria-Delbruck experiment and its key finding
This experiment tested whether mutations arise spontaneously or are induced by selection. By analyzing the fluctuation of phage-resistant bacteria in multiple cultures, it provided evidence that mutations occur randomly and spontaneously before selection is applied.
Describe the SOS response in bacteria.
An error-prone DNA repair mechanism activated by severe DNA damage. It initiates multiple repair processes, but also allows DNA replication without a template, leading to mutations. It is regulated by LexA and RecA proteins.
What are the two main types of DNA repair mechanisms in bacteria?
High-fidelity repair (proofreading, mismatch repair, base excision repair) and error-prone repair (SOS repair).
What are transposable elements?
Stretches of DNA that can move from one site to another within a genome, found inserted into other DNA molecules (plasmids, chromosomes, viral genomes). They cannot replicate independently and carry genes for transposition.
What are the three possible effects of a base-pair substitution in a protein-coding gene?
Missense mutation (changes the amino acid), nonsense mutation (introduces a premature stop codon), and silent mutation (does not change the amino acid).
How can nonsense mutations be suppressed?
By mutations in tRNA genes that alter the anticodon sequence, allowing the tRNA to recognize a stop codon and insert an amino acid. This is not lethal if the cell has multiple tRNA genes for the affected codon.
