OG BB 9

[deleted647690]

In the passage, they mention the enzyme chloramphenicol acetyltransferase, and they also say that they applied the competitive inhibitor chloramphenicol to uncouple translation and transcription, since the enzyme mentioned above is involved in translation elongation.

I chose A for my answer because I figured the question stem was asking, 'How can you make this competitive inhibitor more effective if it is not already effective?' I know that competitive inhibitors can be overcome by increasing the substrate concentration. Therefore, increasing the concentration of inhibitor should help it become effective in inhibiting the enzyme, and thus, A would be correct.

The correct answer was D, and I'm not really sure why. I'm also confused about why they say that chloramphenicol is a competitive inhibitor of chloramphenicol acetyltransferase. Based on the name of the enzyme, isn't chloramphenicol the endogenous ligand? Isn't a competitive inhibitor supposed to be some exogenous ligand (something that isn't usually present in the body/a poison)?

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[Nugester]

I would approach the answer as:
A, B, C all change a variable related to chloramphenicol, so, any of these could be the right answer, so none of them can be the best answer. So D would be the best answer by default. You might feel crappy about doing that on the test, but sometimes you have to resort to testing taking strategies to save time and move on (especially if you don't know what is going on exactly).

Why D is the best answer: nowhere in the passage do they mention temperature, concentration, or time so it would be very difficult to extrapolate what you can change. However, in the passage, they do mention that cat encodes an acetyltransferase to the particular antibiotic. They want you to extrapolate here that it is possible that the acetyltransferase inactivates or weakens chloramphenicol in the cat6xbs strain. So, to uncouple transcription and translation, you may want to use a different antibiotic that isn't influenced by acetyltransferase.

 

[deleted647690]

I would approach the answer as:
A, B, C all change a variable related to chloramphenicol, so, any of these could be the right answer, so none of them can be the best answer. So D would be the best answer by default. You might feel crappy about doing that on the test, but sometimes you have to resort to testing taking strategies to save time and move on (especially if you don't know what is going on exactly).

Why D is the best answer: nowhere in the passage do they mention temperature, concentration, or time so it would be very difficult to extrapolate what you can change. However, in the passage, they do mention that cat encodes an acetyltransferase to the particular antibiotic. They want you to extrapolate here that it is possible that the acetyltransferase inactivates or weakens chloramphenicol in the cat6xbs strain. So, to uncouple transcription and translation, you may want to use a different antibiotic that isn't influenced by acetyltransferase.

Thanks for the response. After reading it again, yeah, I still don't really understand why my interpretation is wrong. But you're right about selecting D as default. I guess I'm missing something major, because I don't really even see how 'antibiotic' comes into play. Again, with chloramphenicol being the endogenous ligand for the chloramphenicol acetyltransferase enzyme, I'm not sure why they are saying that chloramphenicol is an 'antibiotic'

 

[Nugester]

Thanks for the response. After reading it again, yeah, I still don't really understand why my interpretation is wrong. But you're right about selecting D as default. I guess I'm missing something major, because I don't really even see how 'antibiotic' comes into play. Again, with chloramphenicol being the endogenous ligand for the chloramphenicol acetyltransferase enzyme, I'm not sure why they are saying that chloramphenicol is an 'antibiotic'

Even if you are unaware that chloramphenicol is an antibiotic, aceytyltransferase transfers an acetyl group to chloramphenicol. It is important to extrapolate that that reaction will do something to this ligand. It is stated the passage that chloramphenicol uncouples transcription and translation because it competitively competes with a translation enzyme, so translation doesn't occur. In the cat6xbs train, translation occurs. The implication here is that chloramphenicol is inactivated or weakened. By this logic, changing the variables of A, B, C won't do anything because chloramphenicol is "denatured" so to speak. This leaves D as the best answer. Antibiotic comes into play because chloramphenicol is an antibiotic if you look it up. However, even if you are unaware during the exam, the above bolded words still apply.

As for antibiotic resistance; all this means is if they continued to use that strain, it would have resistance because it would have the deactivated chloramphenicol floating around. So for that strain, they would need a different antibiotic. If they used another cat6xbs that didn't have the chloramphenicol treatment, they would instantly use a different antibiotic because they know that acetyltransferase inactives chloramphenicol.

 

[deleted647690]

Even if you are unaware that chloramphenicol is an antibiotic, aceytyltransferase transfers an acetyl group to chloramphenicol. It is important to extrapolate that that reaction will do something to this ligand. It is stated the passage that chloramphenicol uncouples transcription and translation because it competitively competes with a translation enzyme, so translation doesn't occur. In the cat6xbs train, translation occurs. The implication here is that chloramphenicol is inactivated or weakened. By this logic, changing the variables of A, B, C won't do anything because chloramphenicol is "denatured" so to speak. This leaves D as the best answer. Antibiotic comes into play because chloramphenicol is an antibiotic if you look it up. However, even if you are unaware during the exam, the above bolded words still apply.

As for antibiotic resistance; all this means is if they continued to use that strain, it would have resistance because it would have the deactivated chloramphenicol floating around. So for that strain, they would need a different antibiotic. If they used another cat6xbs that didn't have the chloramphenicol treatment, they would instantly use a different antibiotic because they know that acetyltransferase inactives chloramphenicol.

Alright, for some reason it was sticking with me that chloramphenicol was acting on chloramphenicol acetyltransferase; I thought that this enzyme was the one spoken of as causing translation elongation.
So are they saying, for some reason, the tagging of the chloramphenicol acetyltransferase enzyme with cat6xbs renders the antibiotic, chloramphenicol, ineffective?

 

[Nugester]

Alright, for some reason it was sticking with me that chloramphenicol was acting on chloramphenicol acetyltransferase; I thought that this enzyme was the one spoken of as causing translation elongation.
So are they saying, for some reason, the tagging of the chloramphenicol acetyltransferase enzyme with cat6xbs renders the antibiotic, chloramphenicol, ineffective?

Exactly! Remember cat codes for the transferase and that is combined with 6xbs.