Question

What would you predict to be the immediate outcome of adding \(\alpha\) -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 activity of ribosomes translating mRNA

Short answer

The immediate outcome of adding α-amanitin to a cell would be (b) reduced production of one or more types of RNA, specifically mRNA synthesis, as α-amanitin inhibits RNA polymerase II, which is responsible for transcribing mRNA from a DNA template.

Step-by-step solution

Identify the role of RNA polymerase II

RNA polymerase II is an enzyme responsible for transcribing mRNA (messenger RNA) from a DNA template. mRNA molecules are ultimately used in the process of translation, which involves ribosomes synthesizing proteins using the information contained in mRNA. By inhibiting RNA polymerase II, we can expect a reduction in mRNA synthesis.

Analyze each option

a. Reduced DNA synthesis: Since α-amanitin inhibits RNA polymerase II, which is responsible for mRNA synthesis from a DNA template, it is unlikely to directly affect DNA synthesis. b. Reduced production of one or more types of RNA: This option seems plausible as RNA polymerase II is primarily responsible for mRNA synthesis. Inhibiting it would result in reduced mRNA production. c. Reduced binding of tRNAs to anticodons: The process of tRNAs binding to anticodons happens during translation, and α-amanitin specifically affects transcription by inhibiting RNA polymerase II. Thus, it does not directly affect the binding of tRNAs to anticodons. d. Reduced activity of ribosomes translating mRNA: Although reduced activity of ribosomes may happen as a downstream effect of reduced mRNA synthesis, it is not the immediate outcome of adding α-amanitin.

Choose the correct option

Based on the analysis in Step 2, the immediate outcome of adding α-amanitin to a cell will be a reduced production of one or more types of RNA, specifically mRNA synthesis. Therefore, the correct answer is option (b).

Key concepts

α-amanitin

α-amanitin is a potent toxin produced by the *Amanita* genus of mushrooms, famously known for their "death cap" appearance. It exhibits its toxic effects by specifically inhibiting RNA polymerase II, the enzyme pivotal in transcribing messenger RNA (mRNA) in eukaryotic cells.
Here's how α-amanitin operates:

• Selective target: It predominantly affects RNA polymerase II, without heavily impacting other polymerases like I and III.
• Binding with high affinity: It binds and obstructs the active site of RNA polymerase II, halting the transcription process.
• Delayed toxicity: Although the toxin might be ingested, its effects might not be immediate but develop over several hours or even days.

Due to these unique properties, α-amanitin is a significant tool in biological research, allowing scientists to study the transcription mechanics in eukaryotic cells.

mRNA synthesis

mRNA synthesis is a fundamental biological process responsible for converting genetic messages from DNA into a format that can be deciphered and translated into proteins by ribosomes. RNA polymerase II plays a central role in this process. Here’s what mRNA synthesis involves:

• Initiation: RNA polymerase II binds to specific DNA regions called promoters. Here, transcription factors help in positioning the polymerase correctly on the DNA strand.
• Elongation: During this phase, RNA polymerase II traverses the DNA template strand, adding nucleotides to elongate the mRNA strand.
• Termination: Synthesis concludes when RNA polymerase II encounters a termination sequence, leading to the release of the newly synthesized mRNA.

The synthesized mRNA undergoes several processing steps, including splicing, capping, and polyadenylation, making it mature and ready for translation. The interference by α-amanitin drastically reduces mRNA synthesis, thereby impacting the overall protein production in cells.

Transcription Inhibition

Transcription inhibition occurs when the process of synthesizing RNA from DNA is disrupted, usually resulting in decreased or halted production of RNA molecules. This can significantly impede cellular functions, as proteins that are required for various cellular activities depend on mRNA transcripts. Relevant points about transcription inhibition include:

• Role of inhibitors: Agents like α-amanitin specifically inhibit key enzymes, such as RNA polymerase II, stopping transcription.
• Effects on cells: By inhibiting transcription, essential proteins are not produced, leading to cell growth arrest and possibly cell death.
• Biological research applications: Understanding transcription inhibition can provide insights into gene regulation and potential therapeutic targets for diseases with aberrant cell growth patterns, like cancer.

When α-amanitin is used as an inhibitor, it opens a window into understanding the intricate process of transcription, and elucidates how crucial RNA synthesis is for proper cellular functioning.