lab 1 mutants Flashcards
antibiotic
a medicine that inhibits the growth of or destroys microorganisms
antibiotic resistance
the ability of bacteria and other microorganisms to resist the effects of an antibiotic to which they were once sensitive
problem of antibiotic resistance
treatment of an infection with antibiotics can provide selective pressure for the growth of cells that have developed resistance to the drug.
resistance genes can be used as ..?
selectable markers in gene transfer experiments
antibiotics are produced _____?
naturally by many organisms
Rifampicin used to combat ____
infections caused by Mycobacterium tuberculosis and Mycobacterium leprae
auxotroph
a mutant organisms that requires a particular nutrient that the normal strain does not
-a mutant strain that has lost its ability to synthesize one or more essential nutrients
growth factors
- essential nutrients
- required for the growth of bacteria but can normally be produced by a wild type strain when grown in minimal medium
tryptophan synthesis in wild type e.coli example
1) when tryptophan is present in the environment, the wild type E. coli will bring tryptophan into the cell through a cell membrane permease
2) absence of typtophan from the growth medium causes induction of the wild-type E.coli’s trp operon, a set of genes that code for enzymes needed to synthesize tryptophan. transcription of these genes allows the amino acid to be produced inside the cell and eliminates the need to uptake tryptophan from the environment
tryptophan auxotroph
mutant strain that does not have the ability to synthesize its own tryptophan.
-to grow the mutant tryptophan must be provided in the growth medium
carbon source mutant
a strain that has lost its ability to use a carbon source that would normally be used by the wild type
lac- mutant
a carbon source mutant that is incapable of using the sugar lactose
genotypes
three lower case letters in italics. + or - for particular allele for that gene
+ means the gene is present and functioning normally
- gene is missing or non-functional
phenotype
dependent on genotype
-capital first letter, three letters and not italicized
antibiotic phenotype
-genes for antibiotic resistance are normally give na three letter abbreviation with a fourth letter s= sensitive, r=resistant.
defined media
derived from M9 medium
- M9 is a minimal medium, which means that it contains all of the elements needed for growth by the wild type E.coli, but does not contain any growth factors.
- carbon source added for energy, we can also add individual growth factors to the medium that may be required by specific auxotrophs
complex medium
LB agar
- made with peptones and yeast extract, has a variety of growth factors and organic carbon sources j
- peptones excellent source of carbon and energy for mutants
- peptones and yeast extract provide growth factors required by auxotrophs
rifampicin target
gram negative and positive bacteria especially Mycobacterium tuberculosis
rifampicin mode of action
inhibits RNA synthesis by binding to the B subunit of the RNA polymerase so the enzyme cannot bind to DNA
rifampicin mode of resistance
mutation in the B subunit prevents the drug from binding to RNA polymerase
ampicillin targets
gram +ve and -ve
ampicillin mode of action
inhibits peptidoglycan synthesis by preventing cross links from forming
ampicillin mode of resistance
production of the B lactamase enzyme that cleaves the B lactam ring, which inactivates the antibiotic
tetracycline target
gram +ve and -ve
tetracycline mode of action
binds to the 30 S subunit. prevents binding of the aminoacyl tRNA to the A site of the ribosome
tetracycline mode of resistance
organisms actively excretes the drug which prevents it from accumulating inside the cel
streptomycin targets
most effective against gram negatives
streptomycin mode of action
binds to the 30S ribosomal subunit causing tRNA mismatches, which leads to mistranslated proteins
streptomycin mode of resistance
mutations in the rpsL gene (codes for the 30S ribosomal polypeptide) results in the
reduced binding of the drug
calculating the conc. of an antibiotic added to your media
C1V1=C2V2
