3. Explain the growth of E. coli in response to the following conditions of carb
ID: 274571 • Letter: 3
Question
3. Explain the growth of E. coli in response to the following conditions of carbon source availability. How are these responses controlled by the lac operon? Please keep in mind the two types of DNA-binding proteins: repressors (which can accomplish induction or repression), and activatorS a. Glucose; no lactose Why is the lac operon shut down? Where is the repressor protein? b. Glucose; lactose Why is the lac operon still shut down? Where is the repressor protein? What type of repressor is the repressor protein (i.e inducible or repressible)? If the lac operon is no longer blocked by the repressor protein, why doesn't transcription occur? What does this tell us about the effectiveness of the promoter of the lac operon? c. No glucose; no lactose Why is the lac operon shut down? Explain the two DNA-binding proteins involved that prevent transcription. d. No glucose; lactose Why is the lac operon expressed under these conditions? What does the presence of the activator accomplish in terms of the ineffectual promoter of the lac operon? 4. Challenge question: If expression of the lac operon is really blocked by the repressor protein in the absence of lactose (allolactose), how do you think lactose initially gets inside the cell to allow repression to end?Explanation / Answer
a.Glucose, no lactose
the ultimate aim of bacteria is to use glucose as its energy source. Therefore, when , glucose is available in the medium it shuts down the operator to save its energy. When the lac operon is ON, it allows transcription and trasnlatiion of galactosidase enzyme, which cleaves lactose into glucose and galactose.
The repressor protein is bound to the operator region of the operon.
b. Glucose, lactose
to switch ON the lac operon, 1. cAMP-CAP should bind to the promoter region and 2. Repressor should not bind to the operator region.
in the presence of both glucose and lactose, even though the repressor is not bound to the operator region, the concentration of cAMP is low so that it cannot bind to the promoter region. Both the cAMP-CAP and repressor are not bound to operon. Hence, operon would be shut down.
In other words since glucose is available in the medium, there is no use of lac operon. The bacteria can use glucose as its energy source.
The repressor is bound to lactose. It is inducible, i.e, it induces operon when bound to lactose. Tryptophan corepressor blocks the operon when bound to tryptophan.
c. no glucose, no lactose
lac operon is still not expressed because the repressor is still bound to the operator region of the operon.
cAMP-CAP dimer and repressor are the two proteins in the regulation of lac operon.
d. no glucose, lactose
under this condition, cAMP concentration is higher so that cAMP-CAP dimer is bound to promoter region.
since lactose is present in the medium, it binds to repressor and wont allow the repressor to bind to operator region.
4. although, we say that lac expression does not occur, it occurs at minimal levels in all conditions. This allows the lactose to enter the cell and enhance the transcription.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.