Gene regulation in bacteria - Regulation of the lac operon
57 important questions on Gene regulation in bacteria - Regulation of the lac operon
Which researchers investigated gene regulation in the beginning of the twentieth century, and gave us remarkable insights in this phenomenon?
What was the observation of Jacob and Monod of lactose metabolism in E. Coli?
In bacteria, it is common for genes to be arranged in an operon. What is an operon?
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What does an operon encode?
What is an advantage of an operon?
What is the function of β-galactosidase?
- Converts some of the lactose into allolactose (which functions as a small effector molecule for regulating lac operon).
What is lactose permease?
What is the function of galactoside transacetylase?
What is the CAP site?
What is the operator site?
Besides the lac operon, in this part of the DNA is another transcriptional unit present. What is the other one called?
What does the lacI gene encode for?
In which 2 ways can the lac operon be transcriptionally regulated?
2. Catabolite repression.
What does the first way of transcriptional regulation involve?
When is lac repressor bound to the operator site most of the time?
How does allolactose influence the ability of the binding of lac repressor to the operator?
When lac repressor is not able to bind to the operator site, what is the effect on the expression of the lac operon?
How is it called when RNA polymerase is free to transcribe a gene?
How are the sites in an allosteric protein where small effector molecules bind to, called?
In what do mutations in the lacI result?
What are super-repressor mutations?
What happens when a bacterial cell is exposed to lactose (steps)?
2. Beta-galactosidase converts some of the lactose into allolactose;
3. Allolactose binds to lac repressor;
4. Lac repressor falls off the operator site;
5. Lac operon proteins are synthesized and lactose is metabolized.
What happens when all the lactose is depleted?
What did Jacob and Monod initial think of the lacI mutation?
What are F factors?
What is a merozygote?
What kind of F factors identified Jacob and Monod in their studies?
What was the experimental approach of Jacob and Monod?
On which 2 key points was this experimental approach based?
- The genes on the bacterial chromosome and the genes on the F' factor are not adjacent to each other.
What do we now know of the second key point of Jacob and Monod?
How was the experiment of Jacob and Monod set up (steps)?
- They added lactose to one of the two tubes, incubated them and lysed them (to let beta-galactosidase escape from the cells);
- They added ONPG, which makes a yellow product in reaction with beta-galactosidase;
- They measured the yellow color with a spectrophotometer.
What are the results of Jacob and Monod's experiment?
- When no lactose was added to the merozygote, the level of beta-galactosidase was low. When lactose was added, it was high.
How can it be explained that in the merozygote strain even the bacterial chromosomal lac operon was expressed when lactose was added?
What is a trans-effect?
How is a regulatory protein, such as lac repressor, called?
How is a DNA segment that must be adjacent to the genes that it regulates, called?
As discussed up to now, the lac operon is regulated by a repressor protein. By which kind of protein is the lac operon also regulated?
How is this second way of lac operon transcriptional regulation called?
By the presence of which substance is catabolite repression influenced?
What doe the E.coli cells do when they are exposed to both glucose and lactose?
How is the sequential use of two sugars by a bacterium known?
Which sugar is always metabolized preferentially in diauxic growth?
Glucose itself does not bind to a regulatory protein. What kind of molecule does it use?
What happens when a bacterium is exposed to both glucose and lactose?
- CAP does not bind to the CAP site;
- Transcription of lac operon is low.
What happens in the absence of both lactose and glucose?
What happens when only lactose is present?
Why is this mechanism called catabolite repression?
Why does this term seem inaccurate?
Is CAP only used in lac operon?
In what way is the reality more complex than was originally thought?
What is the order in which O1, 2, and 3 and the promoter (P) exist in the lac operon?
To which of the 3 operons does the repressor bind?
The missing of which operon does have the most effect on the level of repression?
What happens when O2 or O3 is missing?
How can the repressor bind to the operator sites, even when they are not close to each other?
What kind of molecule is lac repressor?
By what is the loop in the DNA formed that is needed for repressor to bind?
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