Bacterial Genetics Flashcards
Bacterial genome: haploid or diploid?
haploid. genes exist in single copies.
what is a bacteriophage?
a virus that infects bacteria
describe the bacterial genome
single, double-stranded, circular DNA molecule
what is a transition?
a purine is replaced by a pyramidine or vice versa
what is a transversion
a purine is replaced by another purine, or a pyramidine is replaced by another pyramidine
what is a revertant?
mutation that restores a wild type phenotype
define auxotrophy
the inability to synthesize an essential metabolite such as an amino acid. usually a mutant. the corresponding wild type is called a prototroph (able to synthesize the essential metabolite)
a few qualities of bacteria that allow us to select for them?
auxotrophy, ability/inability to utilize a particular carbon source (lactose/glucose), antibiotic resistance
2 ways that antibiotic resistance arises?
- mutation to become resistant
2. transfer of the mutated resistant genes from one bacterium to another
is the % of antibiotic-resistant organisms proportional to the length of the abx treatment?
NO, resistant bacteria spontaneously arise all the time (prior to abx exposure), and the abx treatment allows them to become the principal component of a new population.
define ‘conditional mutants’. what is an example?
mutations that exhibit a mutant phenotype only under certain conditions. ex: temperature sensitive (ts) mutations: will be normal at permissive temperature, but at a different temp the mutant phenotype is observed. because the mutation allows the protein to assume a normal folding at permissive temp, and at the other temp it folds abnormally.
a ts arginine auxotroph: will it grow at 30’ without added arginine?
yes, at 30’ the mutation is silent. at 42’ it is mutated and requires added arginine.
how can we study bacteria that are very difficult to isolate?
can analyse SSU rRNA. (small subunit rRNA). highly conserved, but is unique to each species. has universal primers but content is unique (?)
describe the structure of a bacteriophage
RNA or DNA genome with protein shell or capsid
how do bacteriophages grow?
by infecting an actively growing bacterial culture. the bacteriophage will cause host cell lysis with the repease of progeny phages.
how are bacteriophages quantified?
via plaque assay. placed on a plate with bacteria, and the halo of bacterial death is observed. look for morphology of plaque (size, clear v turbid).
define lytic and lysogenic
both are categories of the phage life cycle.
lytic: involves phage multiplication and release of newly formed phages, following host cell lysis. virulent phages follow this pathway only
lysogenic: (aka integrative) does not result in production of progeny phage or bacterial killing. the DNA becomes incorporated into the bacterial genome. phage genome then replicates when the bacterial genome replicates.
one quality that differentiates virulent from temperate phages
virulent: only uses lytic pathway, produces clear plaques.
temperate phages: produce turbid plaques because can use either lytic or lysogenic pathways.
in a bacterium that has undergone lysogeny, what could happen if the bacteria is stressed?
if host bacterium encounters stress, the repressor of the prophage may be de-activated and prophage may excise itself, and undergo a lytic cycle, releasing phages.
how do bacteria use restriction enzymes to eliminate consequences of bacteriophage infection?
they use restriction enzymes to cleave the foreign DNA enzymatically at specific DNA sequences.
how to bacteria protect their own DNA from restriction enzymes?
they have enzymes that modify their own DNA on the sequences that the enzymes recognize. ie, methylating an amino acid within that sequence.
what are transposons?
mobile genetic elements that are integrated into bacterial chromonoes or plasmids, and are capable of jumping from one DNA location to another.
what are insertion sequences?
sequences at the ends of transposons that allow them to integrate to various places in the genome.
what are the contents of some transposons?
some transposons contain a gene for antibiotic resistance. some duplicate themselves during transposition so they are also retained at their original site.
name 3 mechanisms of gene transfer in bacteria
- transformation
- transduction
- conjugation
describe transformation
transfer of genetic information to a bacterium following the uptake of naked DNA from outside the cell
describe transduction
transfer of a gene from one bacterium to another by a phage that has mistakenly replaced part of all of its genome with some of its host’s DNA
describe conjugation
sexual reproduction in bacteria. unequal exchange of genetic information between parents. transfer of genetic information that requires direct cell-cell contact. examples include transfer of conjugal plasmids and transfer of portions of the bacterial chromosome by Hfr (high frequency of transfer) strains.
what is the laboratory value of transformation?
recombinant DNA plasmids can be easily introduced into bacteria via transformation.
