MCB Quiz problem 7

The following reaction involving the breakdown of sugar A occurs in a bacterial cell. The gene that codes for the enzyme is part of an operon.
In an experiment, some of the bacterial cells were cultured in three flasks with 100 mg/ml of sugar A added. In flasks 1 and 2, compounds L and M were added respectively. Nothing was added to flask 3. The following results were obtained.


Concentration of B (mg/ml)

Flask 1
Flask 2
Flask 3

Addition of…
L
M
(nothing)
At 0 minutes

0
0
0
At 40 minutes

110
2
98
At 80 minutes

201
3
100
At 120 minutes

250
5
100



a) Which of the compounds (L or M) might be a gene repressor? Explain your answer. (5 marks)


M. The reason is because the function of the repressor is to stop the DNA from getting transcripted. If the concentration of the B is very less, this means that there are very less proteins present inside the cell, and this could be due to the large amount of repressor. The reason is because large amount of repressor will slow down the transcription process. The DNA will be transcripted to produce the enzymes, and therefore the sugar will be able to break down. Lesser amount of B means that there are also not enough amount of enzymes for breaking, and this shows that the transcription process is being slowed down by the repressor, therefore the translation process is also being slowed down, therefore, the proteins being produced are also lesser, therefore, the amount of B is less.

b) Suggest with explanations what compound L might be. (5 marks)

Compound L increases the production of the B, therefore, it could be the enzyme that breaks down the sugar A.
It can also be a inductor which is able to bind with the repressor, and therefore preventing the repressor from binding onto the operator of the DNA, and therefore, it is able to go through more transcription, and therefore going through more translation, and then, it will be able to produce more enzymes that is able to break down the sugar A into B and C, and therefore, the concentration of B increases.