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Ch. 16+17 - Transcription, RNA Processing, and Translation
Chapter 16, Problem 15

Biologists have investigated how fast pre-mRNA splicing occurs by treating cells with a toxin that blocks the production of new pre-mRNAs, then following the rate of splicing of the pre-mRNAs that were transcribed before adding the toxin. Why is addition of a toxin important in this study?

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The addition of a toxin that blocks the production of new pre-mRNAs is crucial because it ensures that only pre-existing pre-mRNAs are present in the cells. This allows researchers to specifically study the splicing of these pre-mRNAs without the interference of newly synthesized ones.
By halting the production of new pre-mRNAs, the toxin helps in isolating the variable of interest, which is the splicing rate of pre-mRNAs already present in the nucleus. This simplifies the experimental design and increases the accuracy of the results.
Using the toxin allows biologists to establish a clear timeline or 'before and after' scenario. They can measure the amount and state of pre-mRNAs at the time of toxin addition and then track changes at specific time intervals thereafter.
The approach of adding a toxin to block new pre-mRNA synthesis helps in quantifying the rate of splicing by comparing the amount of unspliced pre-mRNA over time to the amount of spliced mRNA. This provides a direct measure of splicing efficiency and speed.
This method also helps in understanding the dynamics and kinetics of the splicing machinery in the cell under normal conditions, as any changes in the splicing rate post-toxin addition can be attributed to the cellular mechanisms reacting to the absence of new pre-mRNA synthesis.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pre-mRNA Splicing

Pre-mRNA splicing is a crucial process in eukaryotic gene expression where introns (non-coding regions) are removed from the pre-mRNA transcript, and exons (coding regions) are joined together. This modification is essential for producing mature mRNA that can be translated into proteins. Understanding the splicing mechanism helps researchers determine how gene expression is regulated and how it can be affected by various factors.
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2) RNA Splicing Creates Mature mRNA

Toxin's Role in Experimental Design

In biological experiments, toxins can be used to inhibit specific cellular processes, allowing researchers to study the effects of these inhibitions. By blocking the production of new pre-mRNAs, the toxin enables scientists to focus on the splicing rates of pre-mRNAs that were already present, providing insights into the dynamics and efficiency of the splicing process under controlled conditions.
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Experimental Design Example 1

Rate of Splicing

The rate of splicing refers to how quickly pre-mRNA is processed into mature mRNA. This rate can be influenced by various factors, including the presence of splicing factors, the structure of the pre-mRNA, and external conditions such as the introduction of toxins. Measuring the splicing rate is vital for understanding the efficiency of gene expression and the overall regulation of cellular functions.
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Eukaryotic RNA Processing and Splicing
Related Practice
Textbook Question

A small portion of the human transport protein amino acid sequence is shown here. The upper sequence is associated with darker skin, and the lower sequence is associated with lighter skin. What DNA base-pair change created the light-skin form of the human protein from the gene that coded for the dark-skin form?

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Textbook Question

Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

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Textbook Question

If you wanted to use αα-amanitin to shut down 95 percent of transcription by RNA polymerase II, roughly what concentration of αα-amanitin would you use? Note that the scale on the x-axis of the graph in Question 13 is logarithmic rather than linear, so that each tick mark shows a tenfold higher concentration.

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Textbook Question

The allele of the human transport protein associated with lighter skin is found almost exclusively in people with European ancestry. The other common allele for darker skin, which appears to be the ancestral allele, is found in people with African ancestry. What is a plausible explanation for how the lighter-skin allele came to be so common in those with European ancestry?

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Textbook Question

The primary cause of death from αα-amanitin poisoning is liver failure. Suppose a physician informs you that liver cells die because their rate of protein production falls below a level needed to maintain active metabolism. Given that αα-amanitin is an inhibitor of transcription, you wonder if this information is correct. Propose an experiment to determine whether the toxin also has an effect on protein synthesis.

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