Ch. 17 - Gene Expression: From Gene to Protein

Problem 4

Chapter 17, Problem 4

Which of the following is not true of RNA processing? a. Exons are cut out before mRNA leaves the nucleus. b. Nucleotides may be added at both ends of the RNA. c. Ribozymes may function in RNA splicing. d. RNA splicing can be catalyzed by spliceosomes.

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Identify the correct definitions of terms related to RNA processing: Exons are the coding regions of RNA that are kept in the final mRNA, while introns are the non-coding regions that are removed. RNA splicing involves the removal of introns.

Understand the role of spliceosomes and ribozymes in RNA processing: Spliceosomes are complexes made of proteins and RNA that catalyze the splicing of pre-mRNA. Ribozymes are RNA molecules that can catalyze chemical reactions, including splicing.

Analyze the statement about exons: Recall that exons are the portions of pre-mRNA that are retained in the final mRNA, not removed.

Review the modifications that can occur to RNA: Recognize that in RNA processing, a 5' cap and a poly-A tail are added to the ends of the RNA, which corresponds to nucleotides being added at both ends.

Evaluate each statement based on the information reviewed: Determine which statement is not consistent with the standard process of RNA processing.

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Key Concepts

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

RNA Processing

RNA processing refers to the modifications that pre-mRNA undergoes before it becomes mature mRNA. This includes the removal of introns (non-coding regions) and the joining of exons (coding regions), as well as the addition of a 5' cap and a poly-A tail at the 3' end. These modifications are crucial for the stability, export, and translation of mRNA.

Exons and Introns

Exons are the segments of RNA that are retained and expressed in the final mRNA molecule, while introns are non-coding sequences that are removed during RNA processing. Understanding the distinction between exons and introns is essential for grasping how genes are expressed and how mRNA is prepared for translation into proteins.

Splicing Mechanisms

Splicing is the process by which introns are removed and exons are joined together in pre-mRNA. This can occur through two main mechanisms: the action of spliceosomes, which are large complexes of RNA and protein, or through ribozymes, which are RNA molecules that can catalyze their own splicing. Both mechanisms are vital for the accurate processing of RNA.

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Related Practice

Textbook Question

In eukaryotic cells, transcription cannot begin until a. the two DNA strands have completely separated and exposed the promoter. b. several transcription factors have bound to the promoter. c. the 5′ caps are removed from the mRNA. d. the DNA introns are removed from the template.

Which of the following is not true of a codon? a. It may code for the same amino acid as another codon. b. It never codes for more than one amino acid. c. It extends from one end of a tRNA molecule. d. It is the basic unit of the genetic code.

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Textbook Question

The anticodon of a particular tRNA molecule is a. complementary to the corresponding mRNA codon. b. complementary to the corresponding triplet in rRNA. c. the part of tRNA that bonds to a specific amino acid. d. catalytic, making the tRNA a ribozyme.

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Textbook Question

Which component is not directly involved in translation? a. GTP b. DNA c. tRNA d. ribosomes

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Textbook Question

Using Figure 17.6, identify a 5′→3′ sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys. a. 5′-UUUCCCAAA-3′ b. 5′-GAACCCCTT-3′ c. 5′-CTTCGGGAA-3′ d. 5′-AAACCCUUU-3′

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Textbook Question

Which of the following mutations would be most likely to have a harmful effect on an organism? a. a deletion of three nucleotides near the middle of a gene b. a single nucleotide deletion in the middle of an intron c. a single nucleotide deletion near the end of the coding sequence d. a single nucleotide insertion downstream of, and close to, the start of the coding sequence

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