chapter 9 - bacterial genetics Flashcards
Why do selectable mutations confer an advantage?
progeny cells outgrow and replace parent
relatively easy to detect
powerful genetic tool
What are examples of phenotypes you can detect through screening
- auxotroph
- temperature-sensitive
- cold-sensitive
- rough colony
- pigmentless
- sugar fermentation
What are examples of phenotypes you can detect through selection?
- drug-resistant
- virus-resistant
What does replica plating screen for?
nutritionally defective mutants
What does mutation rate depend on?
frequency of DNA changes and efficiency of DNA repair
What are the two types of mutations
- spontaneous mutation: occurs without external intervention. resulting mainly from errors during DNA replication
- induce mutations: caused environmentally or deliberately. resulting from exposure to radiation or chemicals that modify DNA
What are the different types of base pair mutations?
- silent mutations: do not affect polypeptide sequence
- missense mutation: change sequence of amino acids in polypeptide
- non-sense mutation: stop codon resulting in truncated (incomplete) protein
What is a revertant?
a strain in which original phenotype is restored
What is a true revertant?
restore original sequence
What is a supressor mutation?
mutation at a different site in the genome that restores the original phenotype
What is the mechanism of major DNA repair and SOS system
- major DNA damage activates SOS repair system
- initiates many DNA repair processes
- allows DNA repair without a template by random incorporation of dNTPs
- regulated by Lex A and Rec A proteins
what are the 3 mechanisms of horizontal gene transfers?
- transformation: genetic transfer by which free DNA is incorporated into recipient cell and brings genetic exchange
- transduction: genetic transfer fro bacteriophages
(lytic cycle makes phage) - conjugation: horizontal gene transfer that requires cell to cell contact with plasmid, dna synthesized by rolling circle replication
What are the 3 possible fates of horizontal gene transfers?
- degradation
- replication by itself
- recombination with host genome
What is homologous recombination?
process that results in genetic exchange between homologous DNA from two different sources
What is the mechanism of homologous recombination?
- endonuclease nicks one strand of donor molecule
- helicase separates nicked from other
- single stranded segment binds single-strand binding protein and RecA
- strand invasion happens where base pairing displaces other strand of recipient DNA
- creates intermediates with heteroduplex regions
- strands are separated by enzymes that cut and rejoin to original DNA
