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Chapter 15: Problem 14

What transcripts will be most affected by low levels of \(\alpha\)-amanitin? a. 18S and 28S rRNAs b. 5S rRNAs and tRNAs c. other small nuclear RNAs d. pre-mRNAs

Short Answer

Expert verified
d. pre-mRNAs

Step by step solution

01

Understand \( \alpha \)-amanitin

\( \alpha \)-amanitin is a toxin that specifically inhibits RNA polymerase II, the enzyme responsible for synthesizing pre-mRNAs.
02

Identify RNA Polymerases and Their Functions

RNA Polymerase I transcribes 18S and 28S rRNAs.RNA Polymerase III transcribes 5S rRNAs and tRNAs.RNA Polymerase II transcribes pre-mRNAs and other small nuclear RNAs.
03

Determine the Impact

Since \( \alpha \)-amanitin inhibits RNA polymerase II, the synthesis of pre-mRNAs and other small nuclear RNAs will be most affected.
04

Answer the Question

The transcripts most affected by low levels of \( \alpha \)-amanitin are pre-mRNAs.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

alpha-amanitin
Alpha-amanitin is a potent toxin that is primarily found in certain poisonous mushrooms, such as the Amanita species. This compound is notorious for being a specific inhibitor of RNA polymerase II, an enzyme vital for gene transcription. RNA polymerase II is responsible for synthesizing essential RNA molecules from DNA templates.
When alpha-amanitin binds to RNA polymerase II, it disrupts its function, preventing it from transcribing DNA into RNA. This inhibition has serious consequences for cellular function and survival.
Understanding alpha-amanitin's precise role helps in studying transcription mechanisms and can aid in the development of targeted therapies for diseases.
RNA polymerase II
RNA polymerase II is one of the three key enzymes involved in transcribing RNA from DNA in eukaryotic cells. Each RNA polymerase has its specific function:
鈥� RNA Polymerase I: Transcribes ribosomal RNA (rRNA) genes, including 18S and 28S.
鈥� RNA Polymerase II: Primarily transcribes messenger RNA (mRNA) and certain small nuclear RNAs (snRNAs).
鈥� RNA Polymerase III: Transcribes 5S rRNA and transfer RNA (tRNA).
As the chief enzyme responsible for synthesizing pre-mRNAs, RNA polymerase II plays a central role in the production of proteins. Hence, any inhibition of this enzyme can significantly affect gene expression and cellular function.
pre-mRNAs
Pre-mRNAs, or precursor messenger RNAs, are the initial RNA transcripts synthesized by RNA polymerase II. These molecules undergo various modifications such as capping, polyadenylation, and splicing to become mature mRNAs.
Mature mRNAs then serve as templates for protein synthesis during translation. Because pre-mRNAs are vital for protein production, any interruption in their synthesis, such as through the inhibition of RNA polymerase II by alpha-amanitin, can lead to disruptions in cellular functions and processes.
Given their crucial role in gene expression, pre-mRNAs are a central focus in studies of transcription regulation and genetic diseases.
transcription inhibition
Transcription inhibition occurs when the process of transcribing DNA into RNA is interrupted. This can be due to various factors, such as toxins like alpha-amanitin, which specifically inhibits RNA polymerase II.
Several key points to understand about transcription inhibition include:
鈥� It can lead to reduced gene expression.
鈥� Essential RNAs required for protein synthesis are not formed.
鈥� Cellular activities relying on those proteins can be severely impacted.
In research and medicine, understanding how transcription can be inhibited helps in developing antibiotics, cancer treatments, and studying gene expression control mechanisms.
small nuclear RNAs
Small nuclear RNAs (snRNAs) are an integral part of the RNA processing machinery. They are typically involved in splicing, the process of removing introns from pre-mRNA and joining exons to form mature mRNA.
Key facts about snRNAs:
鈥� They are transcribed by RNA polymerase II and III.
鈥� They combine with proteins to form small nuclear ribonucleoproteins (snRNPs).
鈥� They play a role in the regulation of gene expression.
Inhibition of RNA polymerase II, therefore, affects the synthesis of certain snRNAs. This disruption can hamper the RNA maturation process, further influencing gene expression and cellular functionality.

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Most popular questions from this chapter

\(\begin{array}{|c|c|}\hline \text { Codon on mRNA } & {\text { Amino Acid }} \\\ \hline \mathbf{G C A} & {\text { alanine }} \\ \hline \mathbf{A A G} & {\text { lysine }} \\ \hline \mathbf{G U U} & {\text { valine }} \\ \text { AAU } & {\text { asparagine }} \\ \hline \mathbf{U G C} & {\text { cysteine }} \\ \hline \mathbf{U C G} & {\text { serine }} \\ \hline \mathbf{U C U} & {\text { serine }} \\ \hline \text { UUA } & {\text { leucine }} \\ \hline \text { UAA } & {\text { stop }} \\ \hline\end{array}\) You are given three mRNA sequences: 1\. 5鈥�-UCG-GCA- AAU-UUA -GUU-3鈥� 2\. 5鈥�-UCU-GCA- AAU-UUA -GUU-3鈥� 3\. 5鈥�-UCU-GCA- AAU-UAA -GUU-3鈥� Using the peptide encoded by each of the above, compare the three peptides obtained. How are peptides 2 and 3 different from 1? What would be the consequence for the cell in each case? a. There is a silent mutation in peptide 2 and peptide 3 has a stop codon due to mutation. b. There is a silent mutation in peptide 3 and peptide 2 has a stop codon due to mutation. c. There is a different amino acid in peptide 2 and peptide 3 has a stop codon due to mutation. d. There isn鈥檛 a mutation in peptide 2 and peptide 3 has a stop codon due to mutation.

The AUC and AUA codons in mRNA both specify isoleucine. What feature of the genetic code explains this? a. Complementarity b. Degeneracy c. Nonsense codons d. Universality

What would happen if the 5鈥� methyl guanosine was not added to an mRNA? a. The transcript would degrade when the mRNA moves out of the nucleus to the cytoplasm. b. The mRNA molecule would stabilize and start the process of translation within the nucleus of the cell. c. The mRNA molecule would move out of the nucleus and create more copies of the mRNA molecule. d. The mRNA molecule would not be able to add the poly-A tail on its strand at the 5鈥� end.

Why are the \(?10\) and \(?35\) regions of prokaryotic promoters called consensus sequences? a. They are identical in all bacterial species. b. They are similar in all bacterial species. c. They exist in all organisms. d. They have the same function in all organisms

Radioactive deoxythymidine triphosphate is supplied to the protist Euglena. After an interval of time, the cells are homogenized and different fractions are analyzed for radioactivity content in large nucleic acid molecules. Which fraction will not be labeled? a. nucleus b. mitochondrion c. chloroplast d. plasma membrane
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