bacterial genetics I and II Flashcards
how many copies of genes exist in the bacterial genome?
only one - bacterial genomes are haploid
what is the structure of the bacterial genome?
single, double-stranded circular DNA molecule
what does progeny DNA consist of?
semiconservative replication = progeny molecules are a parental strand and a nascent strand
what is the directionality of bacterial DNA replication? where does it start?
starts at origin of replication
bidirectional from there
what is required for initiation of DNA synthesis?
bacterial origin recognition protein that binds to the origin
what is the genotype?
exact nucleotide sequence of the genome
what is a mutation?
change in genotype - any change in the base sequence of DNA
what does it mean for something to be wild type?
designation of the genotype of an organisms found in the wild
what is phenotype?
observable characteristics of an organism
what is a silent mutation?
mutation that does not give rise to a change in phenotype
why are some mutations silent?
1: genetic code is redundant (ie several 3-letter combinations can code for the same AA)
2: conservative changes in AA may not affect function (so if you change, for example, a valine to an alanine, there might not be a change in function since both are nonpolar)
what are point mutations? what are the types of point mutation (list)?
single base changes
1: transitions
2: transversions
3: missense
4: nonsense
what is a transition?
type of point mutation
purine replaced by a pruine (A to G) or pyrimidine replaced by pyrimidine (C to T)
what is a transversion?
type of point mutation
purine replaced by pyrimidine or vice versa
what is a missense mutation?
type of point mutation
when the mutation results in a change of the AA encoded by a codon
what is a nonsense mutation?
type of point mutation
when the mutation changes the codon to a stop codon => shortened protein
what is a deletion (in terms of mutation)?
removal of one or more nucleotides
what is an insertion (in terms of mutation)?
addition of one or more nucleotides
what is a frameshift?
shift in reading frame caused by the insertion or deletion of nucleotides
what is a revertant mutation? what is the difference between a true revertant and a suppressor?
one that restores a wild type phenotype
true revertants are a reversal of the original mutation, whereas suppressors are mutations that occur at a second site and restore wild type phenotype
how could you directly select for mutants?
grow bacteria on solid agar containing ampicillin
bacteria should die, but if mutated for resistance to ampicillin, will survive
what is auxotrophy?
inability to synthesize an essential metabolite such as an AA
what is an auxotroph? what is a prototroph?
auxotrophs = mutants that lack the ability to synthesize an essential metabolite prototroph = wild type of that
how would you select for auxotrophs?
an auxotroph will only grow on a medium that contains the molecule that they canât make whereas the prototroph will be able to grow on minimal medium (just a nitrogen and phosphate source)
what are the basic mechanisms by which antibiotic resistant strains arise?
1: mutation to antibiotic resistance
2: transfer of antibiotic resistance genes
what are conditional mutations?
mutations that exhibit a mutant phenotype only under certain conditions - eg temp sensitive
what is a temperature sensitive mutation? why does this occur?
type of conditional mutation
some are silent at one temperature (the permissive temperature) but not at the non-permissive temperature
because mutation in protein allows it to assume a normal conformation at the permissive temp but forces it to assume an abnormal conformation at the nonpermissive temp
what is genetic recombination?
process by which two genetic elements combine to form one
what are the three types of genetic recombination? (list)
1: general (homologous) recombination
2: site-specific
3: illegitimate recombination
what is general recombination?
type of genetic recombination
requires extensive DNA homology
what is site-specific recombination?
type of genetic recombination
requires a small region of homology
what is illegitimate recombination?
type of genetic recombination
requires no homology
occurs at a very low freqency
what is small subunit (SSU) rRNA analysis used for?
to quantify bacteria in mixed populations
because SSU rRNA is highly conserved but has enough variability to have a unique sequence for most species
what is the benefit of whole genome sequencing?
reveals pathogenesis related genes and metabolic tendencies and potential weaknesses
permits parallel study and deeper understanding of each
only way to identify obligate intracellular and difficult to culture pathogens
what is a bacteriophage? what do they consist of?
bacterial virus
nucleic acid genome (DNA or RNA) surrounded by a protein shell/capsid
what are bacteriophages used for?
as model systems for research on molecular biology and genetics of virus reproduction
what is the nucleocapsid structure of a bacteriophage?
some with either icosahedral or helical symmetry
others have complex structure = head, tail and tail fibers
what determines the species of bacteria that a bacteriophage infects?
viral coat of proteins of the phage
how would you grow bacteriophages?
infect an actively growing bacterial culture
reproduce and usually cause host cell lysis - release progeny
centrifuge culture to remove lysed cells
bacteriophage in supernatant
how would you quantify bacteriophages?
by plaque assay
phage placed on lawn of sensitive bacteria
measure the amount of death they create
what will a plaque assay tell you about bacteriophages?
quantification
species have different morphology
each plaque has several million phage
what is the lytic pathway?
involves phage multiplication and release of newly formed phage following host cell lysis
what life cycle do virulent phage follow?
the lytic pathway only