Wild type E. coli metabolizes the sugar lactose by expressing the enzyme ß-galactosidase. You have isolated a mutant that you call lac1–, which cannot synthesize ß-galactosidase and cannot grow on lactose (Lac–). During an condition you have a wild type (Lac+) strain carrying a Tn5 insertion known to be near several Lac genes on the E. coli chromosome. You grow P1 phage on this strain and use the resulting phage lysate to infect the lac1– strain, selecting for kanamycin resistance (Kanr). Among 100 Kanr transductants, you find that 82 are Lac– and 18 are Lac+. Express the distance between Tn5 and the lac1– mutation as a cotransduction frequency;

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#Question id: 77

#SCPH05 I Biotechnology

Which of the pairs of molecular structures shown depict enantiomers (enantiomeric forms) of the same molecule?

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#Question id: 1708

#I Life Science/ Life Sciences Group – I-V

When antigen reaches a lymph node in a primed animal:

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#Question id: 16127

#SCPH06 I Botany

You are studying regulation of the yeast enzyme glutamine synthetase (GS), which is encoded by the GLN1 gene. You have isolated two mutants, designated  gln2– and gln3–, that give decreased GS activity. Mating of either gln2– or gln3– haploids to wild type produces heterozygous diploids that show normal amounts of GS expression. When you cross either a gln2– or gln3– haploid to a gln1– strain the resulting diploids show normal expression of GS.

The GLN1 gene shows a rather complex regulation in response to different amino acids. When either glutamate (glu) or glutamine (gln) is added to the medium, the amount of GS expression diminished and when both glutamate and glutamine are added to the medium GS expression is shut off completely. The effects of different mutants on the response to glu and gln are shown below.

Which of the models from best fits these experimental results? Complete the model for the regulation of GLN1 that includes the effects of glu and gln.      

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#Question id: 2661

#SCPH05 I Biotechnology

In the histidine operon, if the codons coding for histidine were removed, which of the following would you predict would happen?

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#Question id: 2072

#I Life Science/ Life Sciences Group – I-V

Which of the following structures would decrease the electrochemical gradient across a membrane?