PLSC 631 - Intermediate Genetics

Prokaryotic Gene Expression Quiz

2. In the E. coli cell, what is the effect of domain bonding in the trp operon attenuator region under low and high cellular concentrations of tryptophan?

3. As mentioned in the text to this topic, a number of mutants have been found in the genes of the lac operon. These include:

I^s - superrepressor; effector molecule does not bind to this protein
I^c - repressor protein that can not bind to the operator
P^- - mutant promoter; RNA polymerase can not bind to the promoterO^c - mutant operator; repressor can not bind
Y^- - mutant permease; can not transport lacotse into the cell

For the following genotypes, determine if the E. coli cell will produce the ß-galactosidase enzyme if the cells are a. grown in the presence of lactose or b. grown in the abscence of lactose.

1. I⁺P⁺O⁺Z⁺Y⁺
2. I^sP⁺O⁺Z⁺Y⁺
3. I^cP^-O^cZ⁺Y⁺
4. I⁺P⁺O⁺Z⁺Y^-
5. I⁺P⁺O^cZ⁺Y^-

4. Microbiologists are able to create stable "partial diploids" of E. coli by introducing genes into the cell on a F' factor. For example, the partial diploid I^cP⁺O⁺Z⁺Y⁺/I⁺P⁺O⁺Z⁺Y⁺ will produce ß-galactosidase in the presence of lactose, but will not produce the enzyme without lactose in the cellular media. Why? Even though on operon has a mutant repressor, the repressor produced from the allele in the other operon can migrate through the cell and control the other operon. Using this same approach determine if these "partial diploids" will express the ß-galactosidase enzyme in a. the prescence of lactose and b. in the abscence of lactose.

1. I⁺P⁺O⁺Z⁺Y⁺/I⁺P⁺O⁺Z⁺Y⁺
2. I⁺P⁺O⁺Z⁺Y⁺/I⁺P⁺O⁺Z⁺Y^-
3. I^sP⁺O⁺Z⁺Y⁺/I⁺P⁺O⁺Z⁺Y⁺
4. I⁺P⁺O^cZ⁺Y⁺/I⁺P⁺O⁺Z⁺Y⁺
5. I⁺P⁺O^cZ⁺Y^-/I⁺P⁺O⁺Z⁺Y^-