#Question id: 2858
#Unit 2. Cellular Organization
When lactose enters the cell, it is converted to allolactose. It is allolactose (rather than lactose itself) that controls the Lac repressor. Paradoxically, the conversion of lactose to allolactose is catalyzed by b-galactosidase, itself encoded by one of the lac genes. How is this possible? Which statement is incorrect according lac genes expressions?
#Question id: 2859
#Unit 2. Cellular Organization
NtrC controls expression of genes involved in nitrogen metabolism by inducing a conformational change in a pre-bound RNA polymerase, triggering transition to the open complex.
I. Under low nitrogen level condition, NtrC is phosphorylated by a kinase, NtrB,
II. NtrC (bound to its sites upstream) interacts directly with s54. This requires that the DNA between the activator binding sites and the promoter form a loop to accommodate the interaction
III. Active NtrC binds four sites located approximately 150 bp upstream of the glnA gene.
IV. NtrC itself has an ATPase activity which provides the energy needed to induce a conformational change in polymerase.
Correct series of Activation by NtrC is;
#Question id: 2860
#Unit 2. Cellular Organization
Lactose metabolism in E. coli is carried out by two enzymes, with possible involvement by a third. The genes for all three enzymes are clustered together and transcribed together from one promoter, yielding a polycistronic message. These three genes, linked in function, are therefore also linked in expression. They are turned off and on together.
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Negative control |
keeps the lac operon repressed in the absence of lactose. |
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positive control |
keeps the operon relatively inactive in the presence of glucose, even when lactose is present. |
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when all the glucose is gone and lactose is present, a mechanism should exist. |
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is mediated by a factor called catabolite activator protein (CAP), which, in conjunction with cyclic-AMP, stimulates transcription. |
#Question id: 2861
#Unit 2. Cellular Organization
What is the result of regulatory mutation in given lac operon in merodiploids
#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
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+ 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 |
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– 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. |