Answer Options: A. The mutant strain synthesizes dNTP building blocks slower tha

Question

Answer Options:

A. The mutant strain synthesizes dNTP building blocks slower than the wild type strain

B. The mutant strain synthesizes DNA faster than the wild-type strain

C. The mutant strain has a polymerase with a defective 5' to 3' polymerase activity

D. The mutant strain has a polymerase with a defective 5' to 3' nuclease activity

I'm leaning towards answer D, because it appears that the mutant strain RNA polymerase laid down 2 dNTP's before stopping. Indicating that there was an error that occurred within the first minute of replication and it was unable to correct itself.

Explanation / Answer

The correct answer for this question is opt A or opt C. Explanation is as follows -

Option B says the mutant strain is synthesizing DNA faster than the wild-type strain, which is clearly not the case as the curve for wild-type strain is way above the curve for mutant-strain.

Option D says the mutant-type strain has a polymerase with a defective 5’ to 3’ nuclease activity. The nuclease activity of a polymerase is defined as its ability to split the bonds between two nucleotides in nucleic acids such as DNA and RNA. It is useful to the polymerase in its proofreading function. Now, here in the graph, we can see that the rate of addition of dNTPs becomes constant after 2 minutes. And it is slow from the very start. This doesn’t imply there is a defect in the proofreading activity of the polymerase. So even if there is a mistake in DNA synthesis, the organism is correcting is and moving on.

Option A says that the mutant-type strain is producing dNTPs much slower. This is the correct conclusion as in the graph, we can see that the rate at which new dNTPs are added is much slower than the wild-type strain. Thus, the organism in consideration is producing dNTPs at a much slower rate.

Option C says the mutant has a polymerase with a defective 5’ to 3’ polymerase activity. As the rate of addition of new dNTPs is slower than the wildtype strain, we can say that the polymerase is "slow" in its activity, thus is a defective polymerase

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