Bacterial Genetics Flashcards
what was the realization of Griffith’s experiment?
that the polysaccharide capsule was preventing the host’s immune system from killing the bacteria
What is meant by high frequency of recomination (Hfr)?
if the F plasmid sequence is integrated into the bacterial chromosome, the cell is designated an Hfr cell
which bacteria can make a sex pilus for conjugation?
gram negative. conjugation of gram positive would be uber rare. if you get sharing of DNA with gram positive it probably wasn’t via a sex pilus.
if conjugation gets interrupted, which genes are most likely to be shared?
the genes closest to the origin of replication on the plasmid
how is conjugation in gram-positive done
they clump together with response to a conjugation related chemical signal- then locally merge cell envelopes, and plasmid DNA is shared using the mechanism as in gram-negative
how big is a bacteria phage?
230nm or .23micrometers
which phages can switch back and forth from lysogenic to lytic?
temperate phages
why would a lysogenic cycle convert to a lytic cycle?
the bacteria could die under exposure to UV radiation, or at high population densities
gene for virulence factor is in fact a viral gene, what implication does this have
virulence gene contains much more cytosine and guanine that most genes (which is also likely to be unmethylated – and so, recognized by TLR 9)
what are some examples of lysogenic conversion with virulence factors
diphtheria toxin, cholera toxin
during which phase of the growth curve is cholera toxin expressed at the highest levels?
end of log phase
what does diphtheria toxin do to eukaryotic cells
destroys their ability to translate proteins
what is an example of homologous recombination
uptake of an alt gene for the transpeptidase enzyme by a beta-lactam sensitive strain of bactera from a bacteria of the same species that was bata-lactam resistant
give an example of nonhomologous recombination
occurs b/w dissimilar DNA sequences and generally produces insertions or deletions or both. Neisseria gonorrheae isolates have been identified that have DNA sequences from human cells in their chromosomes
what makes a bacteria competent?
they express DNA uptake molecules on their cell surfaces. Nucleases on the DNA uptake protein cut and degrade one strand of the DNA, and import the other strand into the cell.
where does the new DNA come from in Natural Transformation?
the environment- you need to have competent bacteria and recombinase which is made by recA gene
What are viruses called that only kill the bacteria they infect?
virulent phages. This is a lytic cycle.
how does the virus get out of the cell in a lytic cycle?
it makes proteins that lyse the bacteria from the inside via proteins
not close relatives: Did this happen all on its own/is the transferred DNA in the recipient’s chromosome?
yes, natural transformation
not close relatives: Does it involve a designed plasmid being shocked into the recipient?
yes, artificial transformation
what would stop both forms of transformation?
DNase added
close relatives: happened with gram-postive bacteria OR transferred DNA is in the recipient/s chromosome: There’s a mention of a lytic phage OR a bunch of random genes are transferred every time
Generalized transduction
close relatives: happened with gram-postive bacteria OR transferred DNA is in the recipient/s chromosome: No phage is necessarily mentioned OR there’s co-transfer of a virulence gene like an A/B toxin plus some other gene
specialized transduction.
Close relatives: A plasmid was transferred/ you can stop the DNA transfer via shaking
conjugation
what is the key mechanism bacteria use to control gene expression
production of different sigma factors under different environmental conditions
what property of pathogenicity in genes could a researcher uses to find their location in a genome?
these genes typically have lots of CGs and very little AT, so you could look for a region with lots of CGs
in general what are anabolic (energy using) pathways down-regulated by?
their end products
in general, what are catabolic (energy generating) pathways up regulated by?
their substrates
the anabolic trp operon codes for enzymes that make tryptophan, if present what would repress transcription of the trp operon?
since all of the genes to make tyrptophan are found on the same operon, if tryptophan is present it will bind to the promoter region and prevent transcription
the catabolic lac operon gene products break down lactose in order to acquire glucose to make ATP. this operon is normally represses how would you relieve repression of the lac operon
if lactose was available, you would bring it into the cell. lactose will pull off the repressor to allow RNA polyerase to transcribe DNA into RNA
explain the transposition mutation
inverted repeats make it more likely that the gen gets moved from one location to another during normal replication. It will now be regulated with the new location and will be subject to that operons control
how does rifampin work?
Disables RNA polymerase –> stops transcription and kills bacteria. Binds in the site on the RNA polymerase where the sigma subunit would have normally bound to inititate transcription of DNA into RNA
How do macrolides work?
They are -“mycin”s that prevent the large subunit from continuing translation (macroSLIDES)
Even though it can vary greatly what is the consensus shine-dalgrano sequence?
AGGAGG
Siderophore
molecule secreted by bacteria to collect iron from the environment, transport iron back into the bacterial cell.
What is the order to Rx 1st gen beta-lactams?
Penicillin, amoxicillin, ampicillin
