In a particular bacterial cell, β-galactosidase is at high concentrations but β-galactoside permease is at very low concentrations. Which is the most likely explanation?
a. Both glucose and lactose are at high concentrations.
b. Both glucose and lactose are at low concentrations.
c. The operator has a mutation.
d. The promoter has a mutation.
e. One of the structural genes has a mutation.
In a particular bacterial cell, β-galactosidase is at high concentrations but β-galactoside permease is at very low concentrations. Which is the most likely explanation?
a. Both glucose and lactose are at high concentrations.
b. Both glucose and lactose are at low concentrations.
c. The operator has a mutation.
d. The promoter has a mutation.
e. One of the structural genes has a mutation.
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Suppose that recombinant DNA technology was used to make a gene in which the structural genes of the lac operon were placed immediately downstream of the promoter and operator of the trp operon. This new operon is then introduced into the chromosome of an E. coli strain that does not have the normal lac operon. Therefore, the only way to get expression of β-galactosidase is from this artificial gene.
Bacteria with this artificial gene were grown under various conditions, and the level of β-galactosidase expression was measured. The effect of mutation of the trpR gene was also evaluated. The results from these experiments are given below:
| presence of tryptophan | presence of glucose | presence of lactose | genotype | Level of β-galactosidase expression: |
| present | absent | present | trpR+ trpO+ | low |
| absent | present | present | trpR+ trpO+ | high |
| present | absent | present | trpR- trpO+ | high |
| absent | present | present | trpR- trpO+ | high |
Can someone please explain to me in detail why the levels of β-galactosidase happened to turn out like this?
