Question

QUESTION 1 Lactose-fermenting bacteria metabolize lactose using two proteins, one binds external lactose and transports it into the cell, the other breaks down the lactose that comes into the cell. The two proteins are coded for by two genes that are under the control of a single promoter. You carry out a lactose fermentation test on an unknown bacterium and find that the result is positive. All of the following are applicable to this bacterium growing in the lactose broth, EXCEPT: A. An operon specific to lactose metabolism is being expressed. B. The proteins involved in lactose metabolism represent part of the bacterium's transcriptome. C. The fact that the bacterium possesses the genes for lactose metabolism means that they are part of its genome. D. A sigma factor would have been involved in initiating expression of the lactose metabolizing genes. E. The lactose metabolism genes would likely have been expressed as part of a polycistronic message (i.e., transcript).

Answer 1

The correct answer is (C) The fact that the bacterium possesses the genes for lactose metabolism means that they are part of its genome.

Reason : Out of the enlisted options, only this option is incorrect. This is because of the fact that it is not necessary for lactose operon to be a part of the genome. The gene can exist in plasmid too, and plasmid is not a part of genome but still its expression takes place. Lac operon doesn't necessarily need to be a part of genome to express those two proteins. Transcript of plasmid is also expressed in bacteria when its translation takes place.

On the other hand, the other 4 options are correct because they are actually occuring in the bacteria. Polycistronic message means the RNA which codes for multiple proteins, and here that's the case. Sigma factor is always required to initiate transcription of lactose metabolizing gene, as it is involved in binding of RNA Polymerase to promoter sequence. The operon is obviously being expressed, that's why those two proteins are formed and give positive result. And finally, proteins involved in lactose metabolism will obviously represent part of transcriptome as the transcriptome is the one which is always getting expressed.

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