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 5b
A portion of a DNA template strand has the base sequence
5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Assume the mRNA is written in the correct reading frame. Determine the amino acid sequence encoded by this fragment. Identify the N- and C-terminal directions of the polypeptide.
Verified step by step guidance1
Step 1: Identify the complementary mRNA sequence by transcribing the DNA template strand. Remember that RNA uses uracil (U) instead of thymine (T). The DNA template strand is read in the 3′ to 5′ direction, so the mRNA will be synthesized in the 5′ to 3′ direction. For example, A pairs with U, C pairs with G, G pairs with C, and T pairs with A.
Step 2: Divide the mRNA sequence into codons (groups of three nucleotides). Each codon corresponds to a specific amino acid or a stop signal during translation.
Step 3: Use the genetic code table to translate each codon into its corresponding amino acid. For example, AUG codes for methionine (start codon), and UAA, UAG, or UGA are stop codons.
Step 4: Determine the directionality of the polypeptide chain. Translation begins at the N-terminal (amino group) and proceeds toward the C-terminal (carboxyl group). The first amino acid corresponds to the start codon, and the sequence ends at the stop codon.
Step 5: Write out the amino acid sequence in order, starting from the N-terminal and ending at the C-terminal. Ensure that you include the start codon and stop translation at the stop codon.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Transcription
Transcription is the process by which the genetic information in DNA is copied into messenger RNA (mRNA). During this process, RNA polymerase binds to the DNA template strand and synthesizes a complementary RNA strand, replacing thymine (T) with uracil (U). Understanding transcription is essential for determining how the DNA sequence translates into an mRNA sequence, which is the first step in protein synthesis.
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Translation
Translation is the process by which the mRNA sequence is decoded to synthesize a polypeptide chain, which will fold into a functional protein. This occurs in the ribosome, where transfer RNA (tRNA) molecules bring specific amino acids to the growing polypeptide chain based on the codon sequence of the mRNA. Recognizing how codons correspond to amino acids is crucial for determining the final amino acid sequence from the mRNA.
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Amino Acid Structure and Polypeptide Directionality
Amino acids are the building blocks of proteins, each consisting of a central carbon atom, an amino group, a carboxyl group, and a variable R group that determines the specific properties of the amino acid. In a polypeptide chain, the N-terminus refers to the end with a free amino group, while the C-terminus has a free carboxyl group. Understanding this directionality is important for correctly identifying the ends of the synthesized polypeptide and its functional implications.
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Related Practice
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.
Textbook Question
A portion of a DNA template strand has the base sequence
5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Which is the third amino acid added to the polypeptide chain?
Textbook Question
Describe three features of tRNA molecules that lead to their correct charging by tRNA synthetase enzymes.
Textbook Question
A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.
On the pedigree, write the genotypes (GG, Gg, or gg) for each person who has been tested or for whom you can deduce a genotype. If a genotype cannot be determined completely, list the alleles you know or deduce must be present.
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