1-10 Bacterial Genetics Flashcards
A) What are biosynthetic genes, catabolic genes, and drug resistance genes?
B) How are strains with these genes referenced?
A) Biosynthetic genes code for substances that the organism is capable of synthesizing on its own (without any help from minimal media). Catabolic genes code for substances that the organism is capable of digesting on its own (so you wouldn’t want to feed it this substance if you need the substance to destroy the organism). Drug resistance genes code for just that.
B) A strain of E. coli pyr- gal- amp would not be able to synthesize pyrimidine or digest galactose, and it would be resistant to ampicillin.
What are operons and operators?
An operon is a cluster of genes with related functions. They share the same regulatory elements, so that they are all activated or deactivated together.
An operator regulates expression of an operon. It separates the promoter and genes, and it can be blocked by a repressor protein.
What is the Ames test?
A basic test of carcinogenicity. Since carcinogens tend to induce spontaneous mutation, the Ames test will return a positive result for carcinogenicity if engineered bacteria (e.g., His auxotrophs) on reduced minimal media (e.g., minus His) are able to reverse mutate and colonize around the carcinogen.
What are the three mechanisms of bacterial gene exchange?
Transformation, conjugation, and transduction.
What is transformation?
A method of bacterial gene exchange by which live bacteria uptake DNA released from dead bacteria.
The uptaken DNA can be chromosomal or plasmid. It can incorporated through homologous recombination, which is more frequent in genetic engineering; this process is rare in nature due to restriction and modification mechanisms.
What is conjugation?
A method of bacterial gene exchange between live bacteria, one of whom has the F factor. The F factor is a large plasmid which contains the genes for conjugation and can function within a chromosome or externally to it. A “male” donor bacterium can transfer the F plasmid + adjacent bacterial DNA to the “female” recipient bacterium, which then becomes male.
F- = female F+ = male without chromosomal integration Hfr = male with integrated plasmid due to high frequency recombination
What are generalized transduction and specialized transduction?
Both are methods of bacterial gene exchange by bacteriophages.
In generalized transduction, a bacteriophage infects and lyses a bacterium, uptakes released DNA, and carries the new DNA into another bacterium via new infection.
In specialized transduction, a lysogenic phage inserts itself into a bacterial chromosome (lysogeny), producing a prophage there. The prophage later excises itself, taking adjacent bacterial DNA with it, and carries it into another bacterium.
What is an R factor?
A plasmid that carries genes for antibiotic resistance.
Large R factors may encode resistance to many different antibiotics.
What are transposons and integrons?
Mobile genetic elements that can move around the genome. They code for enzymes that make transposition possible and can carry other DNA with them. Transposons may relocate to sites where integration with an F plasmid or bacteriophage is possible, or they may integrate with another transposon, producing a compound transposon.
They can be taken up by other bacteria and can encode for drug resistance; compound transposons could confer resistance to multiple drugs in one step.
What are pathogenicity islands?
Regions of bacterial chromosomes with several adjacent genes that contribute to the pathogenesis of a disease. They can be transferred between bacteria via transformation, transduction, or conjugation.
ex) Many Gram(-) bacteria, some strains of E. coli
