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23 Cards in this Set
- Front
- Back
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What do colonies look like on MacLac agar?
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lac+ --> deep red colony, bile salt precipitation b/c acidic byproducts
lac- --> same color as agar |
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What do colonies look like on TZ-Lac agar?
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lac+ --> agar color/clear colonies (acid inhibits TZ dye)
lac- --> red colonies (may have clear halo) |
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What do colonies look like on LB + X-Gal + IPTG agar?
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lacZ+ --> blue colonies
lacZ- --> clear/agar color colonies functional beta-galactosidase cleaves X-gal, yields blue color |
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What phenotype must mutants be to be able to grow on MinMeli agar?
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lacY+ because need lac permease to transport melibiose into cell
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What is the function of IPTG?
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induces transcription of the lac operon (removes lacI repressor).
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What is the significance of phenylgalatcoside (PG)?
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cleaved by lacZ but does not induce lac operon transcription --> only constitutive lac+ mutants can grow on minimal PG agar
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How can replication fork isomerization be used to bypass a lesion in DNA during replication?
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If synthesis of one of the daughter strands is halted due to a lesion in the template:
The daughter strands can peel off the template strands and the longer one can be used as a template to lengthen the short strand, thus bypassing the lesion. |
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What is the average frequency of inserting an incorrect amino acid during protein synthesis?
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1 in 10^4 amino acids
1/10,000 |
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What is the average frequency of errors in DNA replication?
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with DNA polymerase's base selection and proofreading mechanisms, as well as post-replicative mismatch repair:
10^-10, or 1/10,000,000,000 (10 billion) |
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In which direction is the DNA template read during transcription and replication?
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3' to 5'
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In which direction does all polynucleotide synthesis occur?
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5' to 3'
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What is responsible for the frameshift hotspot in the lacI gene?
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3x tandem repeat of CTGG CTGG CTGG --> prone to slippage errors during replication
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What is responsible for the base pair change mutation hotspots in the lacI gene?
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The spontaneous deamination of cytosine to form uracil, resulting in a C:G to T:A mutation
Methylation at these cytosines allows mutations to bypass the uracil DNA-glycosylase repair mechanism. |
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What is the difference between transition and transversion mutations?
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transition mutation: purine and pyrimidine stay on their respective strands, just change to different bp
transversion mutation: purine and pyrimidine switch strands. may be same bp or different bp. |
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What is the difference between positive and negative regulation?
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positive regulation = put something on to activate gene (activator protein)
negative regulation = take something off to activate gene (repressor protein) |
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What determines whether the spontaneous deamination of cytosine will result in a mutation that is passed on to a daughter cell?
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whether the C is methylated or not.
C - (NH2) --> U C-methyl - (NH2) --> T, not recognized by uracil DNA glycosylase |
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What kind of mutant can grow on minimal PG (phenylgalactoside) agar?
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constitutive lacI- mutants, need functional lacZ but not lacY
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What is a cis-acting mutation?
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mutation affecting only the chromosome it is on (ex. an operator mutation)
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What is a trans-acting mutation?
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mutation affecting both its home chromosome and other DNA molecules in cell (ex. a mutated diffusible DNA binding protein)
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What does it mean for two strains to be in different complementation groups?
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Apart the mutants have an incomplete set of functional genes but when their genome are combined they have a complete set.
One makes up for the other's shortcomings |
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Why are most common constitutive merodiploids lacO-?
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lacO- mutations are dominant; a lac operon with a non-functioning operator is not subject to repression even by a super-repressor
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Why are most common constitutive mutants lacI- rather than lacO-?
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lacI gene is a larger target; easier to mess it up because it's bigger and codes for a protein rather than a protein binding site.
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How are amber suppressor tRNAs used to assay for knockout mutations due to bp changes to stop codons?
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function is regained if cell makes suppressor tRNAs that insert amino acids at amber stop codons.
early termination of peptide no longer occurs. |
