Textbook Question
Summarize the steps involved in charging tRNAs with their appropriate amino acids.
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Ch. 14 - Translation and Proteins
Klug12th EditionConcepts of Genetics ISBN: 9780135564776
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Table of contents
- Ch. 1 - Introduction to Genetics17
- Ch. 2 - Mitosis and Meiosis36
- Ch. 3 - Mendelian Genetics51
- Ch. 4 - Extensions of Mendelian Genetics74
- Ch. 5 - Chromosome Mapping in Eukaryotes51
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages46
- Ch. 7 - Sex Determination and Sex Chromosomes33
- Ch. 8 - Chromosome Mutations: Variation in Number and Arrangement40
- Ch. 9 - Extranuclear Inheritance31
- Ch. 10 - DNA Structure and Analysis43
- Ch. 11 - DNA Replication and Recombination44
- Ch. 12 - DNA Organization in Chromosomes30
- Ch. 13 - The Genetic Code and Transcription54
- Ch. 14 - Translation and Proteins47
- Ch. 15 - Gene Mutation, DNA Repair, and Transposition41
- Ch. 16 - Regulation of Gene Expression in Bacteria29
- Ch. 17 - Transcriptional Regulation in Eukaryotes41
- Ch. 18 - Post-transcriptional Regulation in Eukaryotes33
- Ch. 19 - Epigenetics33
- Ch. 20 - Recombinant DNA Technology44
- Ch. 21 - Genomic Analysis36
- Ch. 22 - Applications of Genetic Engineering and Biotechnology36
- Ch. 23 - Developmental Genetics37
- Ch. 24 - Cancer Genetics34
- Ch. 25 - Quantitative Genetics and Multifactorial Traits54
- Ch. 26 - Population and Evolutionary Genetics45
Chapter 14, Problem 11
When a codon in an mRNA with the sequence 5'-UAA-3' enters the A site of a ribosome, it is not recognized by a tRNA with a complementary anticodon. Why not? What recognizes it instead?
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Understand the role of codons and anticodons: Codons are sequences of three nucleotides in mRNA that specify amino acids during translation. Anticodons are complementary sequences on tRNA molecules that pair with codons to deliver the correct amino acid.
Identify the codon in question: The codon 5'-UAA-3' is one of the three stop codons (UAA, UAG, UGA) in the genetic code. Stop codons do not code for any amino acid.
Explain why tRNA does not recognize stop codons: Stop codons are not recognized by tRNA because there are no tRNAs with anticodons complementary to stop codons. This ensures that translation stops at the appropriate point.
Describe what recognizes stop codons: Instead of tRNA, stop codons are recognized by proteins called release factors. These release factors bind to the stop codon in the A site of the ribosome.
Explain the role of release factors: Release factors trigger the hydrolysis of the bond between the polypeptide chain and the tRNA in the P site, releasing the completed polypeptide and terminating translation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Codons and Anticodons
Codons are sequences of three nucleotides in mRNA that specify an amino acid or signal termination during protein synthesis. Each codon is matched by a complementary anticodon found on tRNA molecules, which carry specific amino acids. In the case of the UAA codon, it is a stop codon, meaning it does not have a corresponding tRNA with an anticodon, as it signals the termination of translation.
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Stop Codons
Stop codons are specific codons in mRNA that signal the end of protein synthesis. The three stop codons—UAA, UAG, and UGA—do not code for any amino acids and are recognized by release factors instead of tRNA. When a ribosome encounters a stop codon in the A site, it triggers the release of the newly synthesized polypeptide chain from the ribosome.
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01:55
Translation Termination
Release Factors
Release factors are proteins that recognize stop codons during translation. When a ribosome reaches a stop codon, such as UAA, a release factor binds to the A site, prompting the ribosome to release the completed polypeptide chain. This process is crucial for terminating protein synthesis and ensuring that proteins are properly formed and released.
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08:52F Factor and Hfr
Related Practice
Textbook Question
To carry out its role, each transfer RNA requires at least four specific recognition sites that must be inherent in its tertiary structure. What are they?
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Textbook Question
What are isoaccepting tRNAs? Assuming that there are only 20 different aminoacyl tRNA synthetases but 31 different tRNAs, speculate on parameters that might be used to ensure that each charged tRNA has received the correct amino acid.
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Textbook Question
Discuss the potential difficulties of designing a diet to alleviate the symptoms of phenylketonuria.
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Textbook Question
Individuals with phenylketonuria cannot convert phenylalanine to tyrosine. Why don't these individuals exhibit a deficiency of tyrosine?
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Textbook Question
Early detection and adherence to a strict dietary regimen have prevented much of the intellectual disability that used to occur in those with phenylketonuria (PKU). Affected individuals now often lead normal lives and have families. For various reasons, such individuals tend to adhere less rigorously to their diet as they get older. Predict the effect that mothers with PKU who neglect their diets might have on newborns.
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