Genetics: Analysis and Principles
6th Edition
ISBN: 9781259616020
Author: Robert J. Brooker Professor Dr.
Publisher: McGraw-Hill Education
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Chapter 14, Problem 17CONQ
Mutations in tRNA genes can create tRNAs that recognize stop codons. Because stop codons are sometimes called nonsense codons, these types of mutations that affect tRNAs are called nonsense suppressors. For example, a normal
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A mutation is found in a tRNA-encoding gene. The wild type allele produces a tRNA
that recognizes the codon GAA, and is charged with the amino acid Glutamic acid.
The mutant tRNA is still charged with Glu, but the anticodon is mutated such that it
recognizes the stop codon TAA.
What effect will this have on translation in these cells?
Select all that apply
In the mutant cells, the stop codon TAA will always be bound by the release
factors
In the mutant cells, some of the synthesized proteins will be longer.
O In the mutant cells, the stop codon TAA will sometimes be bound by the mutant
TRNA charged with Glutamic acid.
O In the mutant cells, some of the synthesized proteins will be shorter.
Hemophilia in the Russian royal family was caused by defective protein involved in blood clotting (factor IX). This defective protein was caused by a mutation that altered the splicing of the exons. This genetic change in the splicing pattern created a new stop codon in the mRNA for factor IX.
What effect on the polypeptide chain of factor IX would this new stop codon have?
In bacteria, researchers have isolated strains that carry mutations within tRNA genes. These mutations can change the sequence of the anticodon. For example, a normal tRNATrp gene encodes a tRNA with the anticodon 3′–ACC–5′. A mutation can change this sequence to 3′–CCC–5′. When this mutation occurs, the tRNA still carries a tryptophan at its 3′ acceptor stem, even though the anticodon sequence has been altered.
A. How would this mutation affect the synthesis of polypeptides within the bacterium?
B. What does this mutation tell you about the recognition between tryptophanyl-tRNA synthetase and tRNATrp? Does the enzyme primarily recognize the anticodon or not?
Chapter 14 Solutions
Genetics: Analysis and Principles
Ch. 14.1 - 1. A repressor is a __________ that _________...Ch. 14.1 - 2. Which of the following combinations will cause...Ch. 14.2 - 1. What is an operon?
a. A site in the DNA where...Ch. 14.2 - The binding of _______ to lac repressor causes lac...Ch. 14.2 - Prob. 3COMQCh. 14.2 - How does exposing an E. coli cell to glucose...Ch. 14.3 - When tryptophan binds to trp repressor, this...Ch. 14.3 - During attenuation, when tryptophan levels are...Ch. 14.3 - Operons involved with the biosynthesis of...Ch. 14.4 - 1. Translation can be regulated by
a....
Ch. 14.4 - Prob. 2COMQCh. 14.5 - 1. For a riboswitch that controls transcription,...Ch. 14 - 1. What is the difference between a constitutive...Ch. 14 - In general, why is it important to regulate genes?...Ch. 14 - Prob. 3CONQCh. 14 - Transcriptional regulation often involves a...Ch. 14 - An operon is repressible-a small effector molecule...Ch. 14 - Prob. 6CONQCh. 14 - 7. What is enzyme adaptation? From a genetic point...Ch. 14 - Prob. 8CONQCh. 14 - Prob. 9CONQCh. 14 - Prob. 10CONQCh. 14 - Mutations may have an effect on the expression of...Ch. 14 - 12. Would a mutation that inactivated lac...Ch. 14 - Prob. 13CONQCh. 14 - 14. As shown in Figure 14.12, four regions within...Ch. 14 - 15. As described in Chapter 13, enzymes known as...Ch. 14 - 16. The combination of a 3–4 stem-loop and a...Ch. 14 - 17. Mutations in tRNA genes can create tRNAs that...Ch. 14 - Prob. 18CONQCh. 14 - Prob. 19CONQCh. 14 - A species of bacteria can synthesize the amino...Ch. 14 - 21. Using three examples, describe how allosteric...Ch. 14 - How are the actions of lac repressor and trp...Ch. 14 - 23. Transcriptional repressor proteins (e.g., lac...Ch. 14 - Answer the following questions that pertain to the...Ch. 14 - Chapter 21 describes a blotting method known as...Ch. 14 - As described in experimental question E2 and also...Ch. 14 - Prob. 4EQCh. 14 - Explain how the data shown in Figure 14.9 indicate...Ch. 14 - Prob. 6EQCh. 14 - Lets suppose you have isolated a mutant strain of...Ch. 14 - Prob. 1QSDCCh. 14 - Prob. 2QSDC
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- Several experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAiMet were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ –CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra amino acids, and others contained fewer amino acids than normal. Q. If the same experiment had been conducted on bacterial cells, what results would you expect?arrow_forwardSeveral experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAiMet were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra aminoacids, and others contained fewer amino acids than normal. a. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning. b. If the same experiment had been conducted on bacterial cells, what results would you expect? c. Explain why some of the proteins produced contained extra amino acids while others contained fewer amino acids than normal.arrow_forwardin a clever experiment performed in 1962, a cysteine already attached to its tRNA was chemically converted to an alanine. these “hybrid” tRNA molecules were then added to a cell- free translation system from which the normal cysteine-tRNAs had been removed. When the resulting protein was analyzed, it was found that alanine had been inserted at every point in the polypeptide chain where cysteine was supposed to be. Discuss what this experiment tells you about the role of aminoacyl- tRNA synthetases during the normal translation of the genetic code.arrow_forward
- TRNAS are 'charged' or activated by aminoacyl TRNA synthetases. Select the correct statements regarding this process. The process is dependent on interactions between ribosomes and aminoacyl TRNA synthetases. The aminoacid is added to the D-loop of the tRNA. Aminoacyl TRNA synthetases are pre-associated with tRNAS. The amino acid is attached to the terminal to the 3' hydroxyl of an adenine in the acceptor arm. The process requires an aminoacyl-adenylate intermadiate. QUESTION 19 Select the correct statements regarding myosin-mediated contraction the sarcomere. O Ca2+ is required for the binding of myosin to f-actin. Myosin and f-actin are randomly distributed in the sarcomere. Physical pulling of the actin microfilament requires three distinct conformation changes on myosin that involve ATP binding, ATP hydrolysis and sequential release of inorganic phosphate and ADP. Myosin-mediated contracted is ubiquitous across all cell types. O O O Oarrow_forwardWhich of the following cannot be said regarding aminoacyl tRNA synthetase? It is essential for the correct reading of codons. A single tRNA synthetase can attach different amino acids to their corresponding tRNA. It is first activated when it catalyzes a reaction between ATP and an amino acid to form an aminoacyladenylic acid (amino acyl-AMP). It is responsible for the attachment of the correct amino acid to the correct tRNA. There is a different tRNA synthetase for each amino acid that will be attached to a tRNA.arrow_forwardSeveral experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAi Met were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ –CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra amino acids, and others contained fewer amino acids than normal. a. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning. b. If the same experiment had been conducted on bacterial cells, what results would you expect? c. Explain why some of the proteins produced contained extra amino acids while others contained fewer amino acids than normalarrow_forward
- Mutations that introduce stop codons cause a number of genetic diseases. For example, from 2% to 5% of the people who have cystic fibrosis possess a mutation that causes a premature stop codon in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This premature stop codon produces a truncated form of CFTR that is nonfunctional and results in the symptoms of cystic fibrosis. One possible way to treat people with genetic diseases caused by these types of mutations is to trick the ribosome into reading through the stop codon, inserting an amino acid in its place. Although the protein produced may have one altered amino acid, it is more likely to be at least partly functional than is the truncated protein produced when the ribosome stalls at the stop codon. Indeed, geneticists have conducted clinical trials of a drug called PTC124 on people with cystic fibrosis. This drug interferes with the ribosome’s ability to correctly read stop codons (C. Ainsworth.…arrow_forwardSickle cell disease is caused by a so-called “point mutation" in the human B-globin gene. A point mutation is the result of a single base substitution in the DNA encoding a gene. The sickle cell mutation results in substitution of Val for Glu at position 6 in the B-globin protein. (a) Using the information in Figure 5.18 explain how a point muta- tion could change a codon for Glu to a codon for Val. (b) Do you expect the pI for the sickle cell B-globin to be higher or lower than the pl for wild-type B-globin? Explain.arrow_forwardMutations that introduce stop codons cause a number of genetic diseases. For example, from 2% to 5% of the people who have cystic fibrosis possess a mutation that causes a premature stop codon in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This premature stop codon produces a truncated form of CFTRthat is nonfunctional and results in the symptoms of cystic fibrosis . One possible way to treat people with genetic diseases caused by these types of mutations is to trick the ribosome into reading through the stop codon, inserting an amino acid in its place. Although the protein produced may have one altered amino acid, it is more likely to be at least partly functional than is the truncated protein produced when the ribosome stalls at the stop codon. Indeed, geneticists have conducted clinical trials of a drug called PTC124 on people with cystic fibrosis. This drug interferes with the ribosome’s ability to correctly read stop codons . On the basis of…arrow_forward
- One of the codons in mRNA that specifies the amino acid phenylalanine is UUC. What is the anticodon on the tRNA that carries phenylalanine?arrow_forwardThe genetic code was solved partly by the use of in vitro systems to translate synthetic RNAs into peptides. In these systems, ribosomes, amino acids, and buffers that support translation are added and there is no control of where translation begins. AAA = Lys; AUA = Ile; AAU = Asn; UAA = stop. What peptides would NOT be produced in an in vitro system if the following oligonucleotide were added: AAAAAAAAAUAAAAAAAA Select one: a) Lys-Lys-Lys-Lys-Lys-Lys-Lys-Lys b) Lys-Lys-Ile-Lys-Lys c) Lys-Lys-Asn-Lys-Lysarrow_forwardYou are observing the translation process in a eukaryotic cell that has been exposed to an unknown toxin. About halfway through synthesizing the protein, you note that elongation is stalled. Upon closer observation you notice the polypeptide is attached to the tRNA in the A-site, while the P site is occupied by an uncharged tRNA. A possible mechanism that is inhibiting translation is: Question 21 options: eEF-1βγ (beta-gamma) was inhibited from activating eEF-2. Peptidyltransferase activity was inhibited. eEF-2 was inhibited from being activated. eEF-1βγ (beta-gamma) was inhibited from activating eEF-1α (alpha). eEF-1α cannot be released from the aminoacyl-tRNA in the A-site.arrow_forward
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