Flashcards in Microbio 3-26 genetics Deck (95)
What is the structure of the genome in bacteria?
haploid (single copies), double-stranded, circular DNA molecule
What type of replication does the bacterial undergo?
semi-conservative replication and bidirectional (form the Ori)
How many genes does the bacterial genome encode for?
Define silent mutations.
mutation that does not give rise to a change in phenotype
Why are some mutations silent?
1) the genetic code is degenerate 2) conservative changes in a.a. may not affect the function (ie non-polar -> non-polar)
What are point mutations?
mutations that are single base pair changes
What are transition mutations?
point mutation in a codon that results in a purine -> purine conversion and a pyrimidine -> pyrimidine conversion
What are transversion mutations?
point mutation in a codon that results in a purine -> pyrimidine conversion, and vice versa.
What is missense mutation?
point mutation that changes the codon from one a.a. to another a.a.
What is a nonsense mutation?
point mutation that changes the codon to a stop codon
What is a deletion mutation?
removal of one or more nucleotides
What is an insertion mutation?
addition of one or more nucleotides
What is a frameshift mutation?
shift in reading frame caused by an insertion or deletion of nucleotides
What is a null mutation?
mutation in a gene that leads to its not being transcribed into RNA and/or translated into a functional protein product
What is a revertant? What is the difference between a true revertant and a suppressor revertant?
mutation that restores a WT phenotype. True: reversal of original mutation. Suppressor: mutation that occur at a second site (gene or different location of the same gene that restores WT phenotype)
What is an auxotroph?
mutation that renders the bacteria unable to synthesize an essential metabolite (a.a.); cannot grow on minimal media, must be grown on media supplemented with metabolite
What is a prototroph?
a WT bacterium that can grow on minimal medium.
How would you analyze auxotrophic mutants?
use penicillin enrichment since auxotrophs will not grow in minimal medium containing pencillin whereas prototrophs will grow and be killed (penicillin only kills growing cells). Grow on enrich medium and make a replica plates on minimal medium and look for colonies that did not grow (auxotrophs won't grow)
How do antibiotic resistant strains arise?
1) mutation that results in antibiotic resistance (selective presure). 2) transfer of antibiotic resistance gene.
What is the adaptation theory (Lamarkism)? Can this theory be applied to antibiotic resistant bacteria? If not, what theory would be appropriate?
Adaptation theory: organisms ability to adapt to changes in the environment and adjust accordingly over time. This theory has nothing to do with antibiotic resistant bacteria. The more appropriate theory to be applied to antibiotic resistant bacteria is Darwin's - survival of the fittest.
How does antibiotic resistant organisms arise?
under the selective pressure imposed by antibiotic treatment - only the resistant organisms are able to survive and over time become the principal component of the new population
What are conditional mutants?
mutations that exhibit a mutant phenotype only under certain conditions.
Temperature senstive mutations are what type of mutations? What is the difference between permissive and non-permissive temperatures?
Conditional mutants (mutations that exhibit a mutant phenotype only under certain conditions). Permissive temperatures - mutation allows protein to assume a normal conformation. Non-permissive temperature - mutant phenotype is observed.
What is general (homologous) recombination?
requires extensive DNA homology for two genetic elements to recombine.
What is site-specific recombination?
requires only a small region of DNA homology for two genetic elements to recombine.
What is illegitimate recombination?
requires no DNA homology for two genetic elements to recombine; occurs at a very low frequency (ex: non-homologous recombination, transposition)
Why is SSU rRNA good way to study mixed populations of bacteria? How would you go about detecting SSU rRNA?
small subunit (SSU) ribosomal RNA analysis - where the sequene is highly conserved but has enough variability to have a unique sequence for most species. Amplify the sample using PCR and analyze population using sequencing or on a DNA array
What does whole genome sequencing used to reveal in bacteria? What type of bacteria is it most useful for?
virulence genes (pathogenesis-related genes) and metabolic tendencies (potential weaknesses) of bacteria. Most useful to identifying virulene genes in obligate intracellular and difficult-to-culture pathogens
What is a bacteriophage?
bacterial viruses; simplest life form consisting of a nucleic acid genome surrounded by a protein coat