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Individuals with phenylketonuria cannot convert phenylalanine to tyrosine. Why don't these individuals exhibit a deficiency of tyrosine?
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Ch. 14 - Translation and Proteins
Klug12th EditionConcepts of GeneticsISBN: 9780135564776
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TOC.tableOfContents
- 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
Klug12th EditionConcepts of GeneticsISBN: 9780135564776Non è quello che usi tu?Cambia libro di testo
Capitolo 14, Problema 10
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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Isoaccepting tRNAs are different tRNA molecules that have distinct anticodons but are charged with the same amino acid. These tRNAs recognize different codons in the mRNA that code for the same amino acid, ensuring redundancy in the genetic code.
To address the problem of 20 aminoacyl-tRNA synthetases (enzymes that attach amino acids to tRNAs) and 31 different tRNAs, note that each synthetase must recognize multiple isoaccepting tRNAs for the same amino acid. This recognition is highly specific and relies on structural and sequence features of the tRNA.
One parameter ensuring correct charging is the 'identity elements' on the tRNA. These are specific nucleotide sequences or structural features (e.g., the anticodon loop or acceptor stem) that are recognized by the corresponding aminoacyl-tRNA synthetase.
Another parameter is the proofreading ability of aminoacyl-tRNA synthetases. These enzymes often have an editing site that removes incorrectly attached amino acids, ensuring high fidelity in tRNA charging.
Finally, the spatial conformation of the tRNA and the synthetase's active site ensures a precise fit, allowing only the correct amino acid to be attached to the corresponding tRNA. This structural complementarity is critical for maintaining the accuracy of protein synthesis.
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Isoaccepting tRNAs
Isoaccepting tRNAs are different tRNA molecules that can accept the same amino acid but have different anticodons. This allows for the flexibility in the genetic code, where multiple codons can code for the same amino acid. The presence of isoaccepting tRNAs ensures that the translation process can accommodate variations in mRNA sequences while still producing the correct protein.
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Aminoacyl tRNA Synthetases
Aminoacyl tRNA synthetases are enzymes that catalyze the attachment of specific amino acids to their corresponding tRNAs, forming aminoacyl-tRNAs. There are 20 different synthetases, each specific to one amino acid, ensuring that the correct amino acid is linked to the appropriate tRNA. This specificity is crucial for accurate protein synthesis, as it directly influences the fidelity of translation.
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Charging Mechanism and Fidelity
The charging mechanism refers to the process by which aminoacyl tRNA synthetases attach amino acids to tRNAs. To ensure fidelity, these enzymes utilize several parameters, such as the shape and chemical properties of the amino acid and tRNA, as well as proofreading mechanisms that can correct errors. This ensures that each charged tRNA accurately reflects the intended amino acid, maintaining the integrity of protein synthesis.
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Proofreading
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Domanda del libro di testo
Summarize the steps involved in charging tRNAs with their appropriate amino acids.
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Domanda del libro di testo
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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Domanda del libro di testo
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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Domanda del libro di testo
Assuming that each nucleotide in an mRNA is 0.34 nm long, how many triplet codes can simultaneously occupy the space in a ribosome that is 20 nm in diameter?
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Domanda del libro di testo
Discuss the potential difficulties of designing a diet to alleviate the symptoms of phenylketonuria.
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