Questions: A researcher introduces double-stranded RNA (dsRNA) into a culture of mammalian cells in an effort to stop the expression of a particular protein. The researcher can identify the location of the dsRNA and that of its smaller subsections experimentally, using a fluorescent probe. Some time later, she finds that the introduced RNA separates into single-stranded RNAs, one of which is degraded. Which of the following will provide evidence that the remaining single-stranded RNA is active? - The rate of accumulation of the polypeptide to be translated from the target mRNA is reduced - The amount of miRNA is multiplied by its replication - The cell's translation ability is entirely shut down - The concentration of Drosha is reduced - The rate of single-stranded RNA degradation is increasing

The answer is the first one: the rate of accumulation of the polypeptide to be translated from the target mRNA is reduced.

Explanation for each option:

1. The rate of accumulation of the polypeptide to be translated from the target mRNA is reduced: This option is correct because if the remaining single-stranded RNA is active, it would likely be involved in RNA interference (RNAi) mechanisms. RNAi can lead to the degradation of the target mRNA or inhibit its translation, thereby reducing the accumulation of the corresponding polypeptide.

2. The amount of miRNA is multiplied by its replication: This option is incorrect because miRNA (microRNA) is not typically replicated in this manner. miRNAs are processed from precursor molecules and do not undergo replication like DNA.

3. The cell's translation ability is entirely shut down: This option is incorrect because the introduction of dsRNA targeting a specific mRNA would not shut down the entire translation machinery of the cell. It would specifically affect the translation of the target mRNA.

4. The concentration of Drosha is reduced: This option is incorrect because Drosha is an enzyme involved in the processing of primary miRNA (pri-miRNA) into precursor miRNA (pre-miRNA) in the nucleus. Its concentration is not directly related to the activity of the introduced single-stranded RNA.

5. The rate of single-stranded RNA degradation is increasing: This option is incorrect because an increase in the degradation rate of the single-stranded RNA would suggest that it is being rapidly broken down and not necessarily active in silencing the target mRNA.

Summary: The correct answer is the first one: the rate of accumulation of the polypeptide to be translated from the target mRNA is reduced. This would indicate that the remaining single-stranded RNA is active in interfering with the expression of the target protein.