Textbook Question
Describe the gene and protein defects in phenylketonuria (PKU). How are these defects connected to disease symptoms?
Ch. 9 - The Molecular Biology of Translation
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 9, Problem 3
Several lines of experimental evidence pointed to a triplet genetic code. Identify three pieces of information that supported the triplet hypothesis of genetic code structure.
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Understand that the triplet genetic code hypothesis proposes that three nucleotide bases (a codon) specify one amino acid in a protein sequence.
Consider the experimental evidence from frameshift mutations, where insertions or deletions of one or two nucleotides cause a shift in the reading frame and drastically alter the protein, but insertions or deletions of three nucleotides often restore the reading frame, supporting the idea that codons are triplets.
Examine the work of Crick and Brenner, who showed that adding or removing three nucleotides (or multiples of three) in bacteriophage genes could restore function, indicating that the genetic code is read in sets of three nucleotides.
Look at the biochemical evidence from synthetic RNA experiments (e.g., Nirenberg and Matthaei), where specific trinucleotide sequences were shown to direct the incorporation of specific amino acids during protein synthesis, confirming that codons are triplets.
Review the fact that the number of possible triplet codons (4³ = 64) is sufficient to code for all 20 amino acids plus stop signals, which aligns with the observed complexity of the genetic code.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Frameshift Mutations and Their Effects
Frameshift mutations, caused by insertions or deletions of nucleotides, disrupt the reading frame of mRNA. Experimental evidence showed that adding or removing three nucleotides often restored the original reading frame, supporting the idea that the genetic code is read in triplets.
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Crick, Brenner, and Colleagues’ Experiments
The experiments by Crick and colleagues using bacteriophage T4 demonstrated that mutations in multiples of three nucleotides could restore protein function. This indicated that codons consist of three nucleotides, as changes in triplets preserved the downstream reading frame.
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Triplet Codon Specificity in Protein Synthesis
Early biochemical studies showed that each amino acid is encoded by a sequence of three nucleotides (a codon). This triplet nature explained how 20 amino acids could be specified by combinations of four nucleotides, providing a logical framework for the genetic code.
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Related Practice
Textbook Question
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
What was the result of studies of synthetic mRNAs composed exclusively of cytosine?
Textbook Question
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
What result was obtained for synthetic mRNAs containing AG repeats, that is, AGAGAGAG...?
Textbook Question
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
Predict the results of experiments examining GCUA repeats.
Textbook Question
Outline the events that occur during initiation of translation in E. coli.
Textbook Question
A portion of a DNA template strand has the base sequence
5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Identify the sequence and polarity of the mRNA transcribed from this fragmentary template-strand sequence.