#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 |
#Question id: 2869
#Unit 2. Cellular Organization
Galactose imported into the yeast cell is converted to galactose 6-phosphate by a pathway involving six enzymes, whose genes are scattered over three chromosomes. Transcription of these genes is regulated by the combined actions of the proteins Gal4p, Gal80p, and Gal3p,
|
i. GAL3 |
a. Interaction with the Gal80p-Gal4p complex and activates Gal4p. |
|
ii. GAL4 |
b. Recruits SAGA, Mediator, and TFIID to the galactose promoters, leading to DNA polymerase II recruitment and initiation of transcription |
|
iii. GAL80 |
c. Transcriptional inhibitor |
|
d. Transcriptional activator |
#Question id: 2870
#Unit 2. Cellular Organization
In Escherichia coli, the synthesis of tryptophan is controlled by the tryptophan operon that is repressed in the presence of excessive tryptophan. When a mutant strain that has lost the regulatory gene of the tryptophan operon is placed in a medium that contains all nutrients the cells need to grow except tryptophan, which of the following will occur?