#Question id: 2862
#Unit 2. Cellular Organization
What is the result of regulatory mutation in given lac operon in merodiploids,
#Question id: 2863
#Unit 2. Cellular Organization
The promoter of the araBAD operon from E. coli is activated in the presence of arabinose and the absence of glucose and directs expression of genes encoding enzymes required for arabinose metabolism. Unlike the cases of lac and gal genes, where a repressor and an activator work together, here two activators work together: AraC and CAP
|
+ arabinose |
AraC binds that sugar and adopts a configuration that allows it to bind DNA as a dimer to the adjacent half-sites, araI1 and araI2 |
|
– arabinose |
the AraC dimer adopts a different conformation and binds to araO2 and araI1, there is no monomer at site araI2, and so the protein cannot activate the araBAD promoter (araPBAD). This promoter is also controlled by CAP. |
#Question id: 2864
#Unit 2. Cellular Organization
In E. coli, the five contiguoustrp genes encode enzymes that sythesize the amino acid tryptophan. These genes are expressed efficiently only when tryptophan is limiting. The genes are controlled by a repressor, just as the lac genes are, although in this case, it is the absence of its ligand (tryptophan) that relieves repression, match trp genes to their gene product,
|
Trp genes |
Gene products |
|
trpE |
anthranilate
synthetase |
|
trpD |
phosphoribosyl
anthranilate transferase |
|
trpC |
phosphoribosyl
anthranilate isomerase-indole glycerol phosphate synthetase |
|
trpB |
tryptophan
synthetase beta |
|
trpA |
tryptophan
synthetase alpha |
#Question id: 2865
#Unit 2. Cellular Organization
The trp operon is controlled by repression and attenuation, providing a two-stage response to progressively more stringent tryptophan starvation. But attenuation alone can provide robust regulation: other amino acid operons such as leu and his rely entirely on attenuation for their control. Correct number of codons in leader peptide of leu & his operon in a row;
#Question id: 2867
#Unit 2. Cellular Organization
Deletion in region 3 enhances operon or rate of transcription (in trp operon); Choose an incorrect statement.
#Question id: 2868
#Unit 2. Cellular Organization
Given the following mutants and conditions, predict the expression of the of the lacZ gene (no expression, basal level of expression, or activated level of expression). A mutant of E. coli that has a mutation in the operator of the lac operon that prevents the repressor from binding
|
Glucose |
Lactose |
Expression |
|
+ |
- |
1 |
|
+ |
+ |
2 |
|
- |
- |
3 |
|
- |
+ |
4 |