Ch. 17 - Gene Expression: From Gene to Protein

Problem 2

Chapter 17, Problem 2

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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Understand the definition of a codon: A codon is a sequence of three nucleotides on an mRNA molecule that specifies a particular amino acid or a stop signal during protein synthesis.

Analyze option a: Recognize that the genetic code is degenerate, meaning multiple codons can code for the same amino acid.

Analyze option b: Recall that each codon codes for only one specific amino acid or a stop signal, adhering to the principle of the genetic code's specificity.

Analyze option c: Understand the structure and function of tRNA. tRNA molecules have an anticodon region that pairs with the codon on mRNA during translation, not extending from one end of the tRNA.

Analyze option d: Confirm that a codon is indeed a basic unit of the genetic code, as it directly corresponds to an amino acid or a stop signal in the genetic code.

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Key Concepts

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

Codon Definition

A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid during protein synthesis. Each codon corresponds to one of the 20 amino acids or serves as a stop signal, playing a crucial role in translating genetic information into functional proteins.

Degeneracy of the Genetic Code

The genetic code is described as degenerate because multiple codons can code for the same amino acid. This redundancy helps to minimize the impact of mutations, as changes in the DNA sequence may not always lead to changes in the protein produced.

tRNA and Codon-Anticodon Interaction

Transfer RNA (tRNA) molecules have an anticodon region that is complementary to the codon on mRNA. This interaction ensures that the correct amino acid is added to the growing polypeptide chain during translation, with each tRNA carrying a specific amino acid corresponding to its anticodon.

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Interspecific Interactions

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.

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 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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Textbook Question

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

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