Question 1

If CAP could not bind to its CAP site, then what would be the result? Assume lactose is present in each scenario.

Accepted Answer

Catabolite activator protein (CAP) binding is essential for activating transcription in the absence of glucose. When CAP cannot bind to its site, transcription of operons like the lac operon, which requires CAP for activation in low-glucose conditions, becomes difficult to activate.

Question 2

In Jacob, Monod, and Pardee's experiment, what would have been the conclusion if all four tubes produced a yellow color when b-ONPG was added?

Accepted Answer

If all four tubes produced a yellow color when b-ONPG was added, it would indicate that the lac operon is constitutive, meaning that the lac genes are always being transcribed and translated regardless of the presence of lactose or the functionality of LacI. This suggests that LacI does not provide the binding site for the repressor (B), as there would be no repression occurring. It also suggests that LacI does not encode a diffusible repressor (C), as there would be no way for the repressor to act on the operon if it were constitutive. The addition of too much b-ONPG (D) would not necessarily produce a yellow color in all tubes, as the concentration of b-ONPG would be the same in all tubes.

Question 3

Enzymes involved in metabolism are most likely regulated via ________.

Accepted Answer

Enzymes involved in metabolism are often regulated via feedback inhibition, which occurs when the end product of a metabolic pathway acts as an inhibitor for an earlier enzyme in the pathway. This helps to ensure that the pathway is only used when needed and that the end product is not overproduced. Acetylation and methylation are forms of post-translational modification that can affect enzyme activity, but they are not the primary means of regulation for metabolic enzymes.

Question 4

A deletion in an operon removes the terminator. How will that affect the transcript that is produced from the operon?

Accepted Answer

If the terminator is removed, transcription will continue beyond the normal ending point of the operon. This will result in a transcript that is longer than normal.

Question 5

In the lac operon, the CAP site is located next to the ________. When both lactose and glucose are present, this leads to a rate of transcription that is ________.

Accepted Answer

The CAP site is located next to the promoter in the lac operon. When both lactose and glucose are present, the level of cAMP in the cell is low, which means that the CAP protein will not bind to the CAP site. This results in a lower rate of transcription from the promoter. Therefore, the correct choice is D, promoter, low.

Question 6

For these questions, match the following to its appropriate letter. Use each letter only once.
A) lacI gene product
B) Operator
C) Allolactose
D) Lac operon
E) Trp operon
F) Tryptophan
-Inducer

Accepted Answer

The answer of For these questions, match the following to...

Question 7

For these questions, match the following to its appropriate letter. Use each letter only once.
A) lacI gene product
B) Operator
C) Allolactose
D) Lac operon
E) Trp operon
F) Tryptophan
-Co-repressor

Accepted Answer

The answer of For these questions, match the following to...

Question 8

What is the gene responsible for attenuation in the trp operon?

Accepted Answer

The trpL gene encodes a leader peptide that plays a role in attenuation, which is the process of premature termination of transcription in the trp operon. When there are high levels of tryptophan (the end product of the trp operon), the trpL leader peptide is synthesized, which allows the mRNA to form a hairpin loop structure that causes RNA polymerase to prematurely terminate transcription. This mechanism ensures that the cell does not waste energy producing tryptophan when it is already abundant in the environment. The other choices (trpR, trpD, and trpC) are not directly involved in attenuation.

Question 9

For these questions, match the following to its appropriate letter. Use each letter only once.
A) lacI gene product
B) Operator
C) Allolactose
D) Lac operon
E) Trp operon
F) Tryptophan
-Inducible

Accepted Answer

The answer of For these questions, match the following to...

Question 10

What would be the result if the U-rich sequence after the fourth stem loop in the trp operon was replaced by a UG-rich sequence?

Accepted Answer

The U-rich sequence after the fourth stem loop in the trp operon is crucial for the formation of a transcription termination loop (attenuator) when tryptophan levels are high, allowing RNA polymerase to disassociate from the DNA. Replacing this sequence with a UG-rich sequence would likely disrupt this mechanism, preventing proper termination of transcription under high tryptophan conditions, hence attenuation would not occur if tryptophan was high.

Question 11

For these questions, match the following to its appropriate letter. Use each letter only once.
A) lacI gene product
B) Operator
C) Allolactose
D) Lac operon
E) Trp operon
F) Tryptophan
-Repressible

Accepted Answer

The answer of For these questions, match the following to...

Question 12

Which of the following is an example of post translational regulation in prokaryotes?

Accepted Answer

Post translational regulation refers to modifications or regulatory events that occur after the translation of a protein. In prokaryotes, phosphorylation of enzymes is a common form of post translational regulation, allowing for the activation or deactivation of specific enzymes. Options A, C, and D are not examples of post translational regulation but rather refer to events that occur during transcription or translation. Sterically blocking the ribosome occurs during translation initiation, incorporation of antisense RNA occurs during transcriptional regulation, and altering the structure of mRNA also occurs during transcription.

Question 13

A gene is inducible and under negative control. Which of the following pairs will allow expression of this gene?

Accepted Answer

If a gene is inducible, that means its expression can be turned on in the presence of an inducer. However, if it is under negative control, that means a repressor must be present to prevent its expression. Therefore, the only pair that would allow expression of this gene is a repressor and an inducer. The repressor would be bound to the operator region of the gene, preventing transcription. When an inducer is present, it binds to the repressor and inactivates it, allowing transcription of the gene to occur.

Question 14

How many promoters are in an operon?

Accepted Answer

An operon typically has one promoter region, which is where RNA polymerase binds to initiate transcription of the genes within the operon. While some operons may have multiple transcription start sites within the promoter region, there is generally only one primary promoter sequence that is recognized by RNA polymerase. Therefore, the most accurate answer is A) 1.

Question 15

A deletion in an operon removes the promoter. How will that affect the transcript that is produced from the operon?

Accepted Answer

A promoter is required for transcription to occur because it allows for the binding of RNA polymerase to the DNA. Without a promoter, transcription cannot initiate and no transcript will be produced.

Question 16

An activator is present and results in the increase in transcription of the target gene. This is an example of ________.

Accepted Answer

Positive control refers to the regulation of gene expression by regulatory proteins, such as activators, which enhance transcription. In this scenario, the presence of an activator is increasing transcription of the target gene, which is an example of positive control.

Question 17

For these questions, match the following to its appropriate letter. Use each letter only once.
A) lacI gene product
B) Operator
C) Allolactose
D) Lac operon
E) Trp operon
F) Tryptophan
-Cis-acting element

Accepted Answer

The answer of For these questions, match the following to...

Question 18

Allosteric regulation is accomplished by

Accepted Answer

Allosteric regulation involves a small molecule, known as an allosteric effector, binding to a site on the enzyme that is not the active site. This binding causes a conformational change in the enzyme that either enhances or inhibits its activity.

Question 19

What stem-loop conformations favor attenuation?

Accepted Answer

The 1-2 and 3-4 stem-loop conformations favor attenuation by forming a terminator structure that halts transcription.

Question 20

In Jacob, Monod, and Pardee's experiment, how many functional copies of lacI were there in the merozygote?

Accepted Answer

In Jacob, Monod, and Pardee's experiment, the merozygote condition involved one functional copy of the lacI gene, which is responsible for producing the repressor of the lac operon.

Quiz 14: Gene Regulation in Bacteria

If CAP could not bind to its CAP site, then what would be the result? Assume lactose is present in each scenario.

In Jacob, Monod, and Pardee's experiment, what would have been the conclusion if all four tubes produced a yellow color when b-ONPG was added?

Enzymes involved in metabolism are most likely regulated via ________.

A deletion in an operon removes the terminator. How will that affect the transcript that is produced from the operon?

In the lac operon, the CAP site is located next to the . When both lactose and glucose are present, this leads to a rate of transcription that is .

For these questions, match the following to its appropriate letter. Use each letter only once. A) lacI gene product B) Operator C) Allolactose D) Lac operon E) Trp operon F) Tryptophan -Inducer

For these questions, match the following to its appropriate letter. Use each letter only once. A) lacI gene product B) Operator C) Allolactose D) Lac operon E) Trp operon F) Tryptophan -Co-repressor

What is the gene responsible for attenuation in the trp operon?

For these questions, match the following to its appropriate letter. Use each letter only once. A) lacI gene product B) Operator C) Allolactose D) Lac operon E) Trp operon F) Tryptophan -Inducible

What would be the result if the U-rich sequence after the fourth stem loop in the trp operon was replaced by a UG-rich sequence?

For these questions, match the following to its appropriate letter. Use each letter only once. A) lacI gene product B) Operator C) Allolactose D) Lac operon E) Trp operon F) Tryptophan -Repressible

Which of the following is an example of post translational regulation in prokaryotes?

A gene is inducible and under negative control. Which of the following pairs will allow expression of this gene?

How many promoters are in an operon?

A deletion in an operon removes the promoter. How will that affect the transcript that is produced from the operon?

An activator is present and results in the increase in transcription of the target gene. This is an example of ________.

For these questions, match the following to its appropriate letter. Use each letter only once. A) lacI gene product B) Operator C) Allolactose D) Lac operon E) Trp operon F) Tryptophan -Cis-acting element

Allosteric regulation is accomplished by

What stem-loop conformations favor attenuation?

In Jacob, Monod, and Pardee's experiment, how many functional copies of lacI were there in the merozygote?