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

Problem 11

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Chapter 16, Problem 11

Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called αα-amanitin, a toxin that inhibits transcription.What would you predict to be the immediate outcome of adding αα-amanitin to a cell? a. reduced DNA synthesis b. reduced production of one or more types of RNA c. reduced binding of tRNAs to anticodons d. reduced rate of translocation of ribosomes translating mRNA

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Understand the function of α-amanitin: α-amanitin specifically inhibits RNA polymerase II, which is crucial for the synthesis of mRNA in eukaryotic cells.

Relate the function of RNA polymerase II to the options: Since RNA polymerase II is responsible for mRNA synthesis, inhibiting this enzyme would directly affect the production of mRNA.

Eliminate unrelated options: DNA synthesis is carried out by DNA polymerases, not RNA polymerase II, so option a is incorrect. The binding of tRNAs to anticodons and the translocation of ribosomes are part of translation, not transcription, making options c and d incorrect.

Identify the correct outcome: With the inhibition of RNA polymerase II, the production of mRNA will be reduced. This leads to a decrease in the overall synthesis of proteins, as mRNA is the template for protein synthesis.

Choose the correct answer: The immediate outcome of adding α-amanitin to a cell is reduced production of one or more types of RNA, specifically mRNA. Therefore, the correct answer is option b.

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Key Concepts

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

Transcription

Transcription is the process by which the genetic information in DNA is copied into messenger RNA (mRNA). This process is essential for gene expression, as it allows the information stored in DNA to be translated into proteins. Inhibition of transcription can lead to a decrease in RNA production, affecting the overall cellular function and protein synthesis.

α-amanitin

α-amanitin is a potent toxin found in the death cap mushroom that specifically inhibits RNA polymerase II, the enzyme responsible for synthesizing mRNA in eukaryotic cells. By blocking this enzyme, α-amanitin prevents the transcription of genes, leading to a significant reduction in the production of mRNA and, consequently, proteins necessary for cell survival and function.

RNA Production

RNA production refers to the synthesis of various types of RNA, including mRNA, rRNA, and tRNA, which are crucial for protein synthesis and other cellular processes. A reduction in RNA production, particularly mRNA, can severely impact a cell's ability to produce proteins, leading to impaired cellular functions and potentially cell death, especially in the presence of a toxin like α-amanitin.

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Related Practice

One of the possibilities considered about the genetic code was that the code was overlapping, meaning that a single base could be part of up to three codons. How many amino acids would be encoded in the sequence 5′-AUGUUACGGAAU-3′ by a non-overlapping and a maximally overlapping triplet code? a. 4 (non-overlapping) and 16 (overlapping) b. 4 and 12 c. 4 and 10 d. 12 and 4

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Textbook Question

Controlling the rates of transcription and translation is important in bacteria to avoid collisions between ribosomes and RNA polymerases. Calculate what the maximum rate of translation by a ribosome in a bacterial cell would have to be, in units of amino acids per second, so as not to overtake an RNA polymerase that is synthesizing mRNA at a rate of 60 nucleotides per second. How long would it take for this bacterial cell to translate an mRNA containing 1800 codons?

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Textbook Question

Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele? a. a missense mutation b. a frameshift mutation c. a neutral mutation d. a silent mutation

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Textbook Question

Investigators examined the expression of transporter mRNA and protein produced in zebrafish homozygous for each of the alleles and obtained the results summarized here (+ = present, −= absent). Does the allele associated with light color appear to be altering transcription or translation? Why?

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Textbook Question

α-Amanitin inhibits transcription by binding inside an RNA polymerase to a region other than the active site that catalyzes addition of a nucleotide to the RNA chain. Based on the model of RNA polymerase shown in Figure 17.3, predict how the toxin might function to inhibit transcription.

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Textbook Question

Toxins like αα-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of αα-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of αα-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with αα-amanitin will have a reduced level of: a. tRNAs b. rRNAs c. snRNAs d. mRNAs

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