Concepts of Genetics (12th Edition)
12th Edition
ISBN: 9780134604718
Author: William S. Klug, Michael R. Cummings, Charlotte A. Spencer, Michael A. Palladino, Darrell Killian
Publisher: PEARSON
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Textbook Question
Chapter 9, Problem 3NST
DNA in human mitochondria encodes 22 different tRNA molecules. However, 32 different tRNA molecules are required for translation of proteins within mitochondria. Explain.
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Many clinically relevant mitochondrial diseases are caused by mutations in mitochondrial genes affecting tRNAs. For example, one form of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is caused by a point mutation in the gene encoding the mitochondrial tRNA whose anticodon recognizes the codons 5' UUA and 5' UUG. The mutation makes the aminoacylation of this tRNA inefficient.
a. The rate of synthesis of most mitochondrial proteins is either unaffected or slightly decreased in MELAS cells, but one mitochondrial protein called NAD6 is synthesized at only 10% of the normal rate. How is it possible that the translation of this single mitochondrial protein might be affected specifically?
How does the cell ensure that a specific amino acid (say, valine) attaches itself only to the one tRNA molecule that is specific for valine?
(A) Proteins called aminoacyl DNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct DNA molecules carrying the right anticodon.
(B) Lipids called aminoacyl tRNA synthetases are responsible for bringing together the proper pair. The lipid binds the amino acid and one of the correct tRNA molecules carrying the right codon.
(C) Enzymes called aminoacyl tRNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct tRNA molecules carrying the right anticodon.
(D) Enzymes called peptidyl mRNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct mRNA molecules carrying the right anticodon.
The charging of a tRNA with an amino acid can be represented by the following equation:amino acid + tRNA + ATP → aminoacyl-tRNA + AMP + PPI where PPI is pyrophosphate (see figure 3–40). in the aminoacyl-tRNA, the amino acid and tRNA are linked with a high-energy covalent bond; a large portion of the energy derived from the hydrolysis of ATP is thus stored in this bond and is available to drive peptide bond formation at the later stages of protein synthesis. the free-energy change of the charging reaction shown in the equation is close to zero and therefore would not be expected to favor attachment of the amino acid to tRNA. Can you suggest a further step that could drive the reaction to completion?
Chapter 9 Solutions
Concepts of Genetics (12th Edition)
Ch. 9 - Chlamydomonas, a eukaryoric green alga, may be...Ch. 9 - In aerobically cultured yeast, a petite mutant is...Ch. 9 - DNA in human mitochondria encodes 22 different...Ch. 9 - Prob. 4NSTCh. 9 - Why did Marcia choose mitochondrial testing to...Ch. 9 - Marcia saw an ad on television for ancestry DNA...Ch. 9 - How much importance should we place on the results...Ch. 9 - HOW DO WE KNOW? In this chapter, we focused on...Ch. 9 - Review the Chapter Concepts list on page 196. The...Ch. 9 - Streptomycin resistance in Chlamydomonas may...
Ch. 9 - A plant may have green, white, or green-and-white...Ch. 9 - In diploid yeast strains, sporulation and...Ch. 9 - Predict the results of a cross between ascospores...Ch. 9 - In Lymnaea, what results would you expect in a...Ch. 9 - In a cross of Lymnaea, the snail contributing the...Ch. 9 - In Drosophila subobscura, the presence of a...Ch. 9 - A male mouse from a true-breeding strain of...Ch. 9 - Consider the case where a mutation occurs that...Ch. 9 - What is the endosymbiotic theory, and why is this...Ch. 9 - In an earlier Problems and Discussion section (see...Ch. 9 - Mitochondrial replacement therapy (MRT) offers a...Ch. 9 - The specification of the anteriorposterior axis in...Ch. 9 - The maternal-effect mutation bicoid (bcd) is...Ch. 9 - (a) In humans the mitochondrial genome encodes a...Ch. 9 - Mutations in mitochondrial DNA appear to be...Ch. 9 - Researchers examined a family with an interesting...Ch. 9 - Payne, B. A. et al. (2013) present evidence that a...Ch. 9 - As mentioned in Section 9.3, mtDNA accumulates...Ch. 9 - Because offspring inherit the mitochondrial genome...
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- Many blood clotting proteins undergo a post-translational modification in which specific glutamic acid residues (Glu) in the protein are converted to gamma-carboxyglutamic acid residues (Gla). See reaction scheme below. An example is the blood clotting protein Factor IX, which has 12 Glu in its N-terminus converted to Gla. This modification gives Factor IX the ability to bind calcium and phospholipid membranes. Bacteria do not have the enzyme required to convert Glu to Gla and therefore Factor IX proteins expressed in bacteria would not have the proper modifications. How might you engineer the translational apparatus of a bacterial cell line so that it produces Factor IX with Gla in the appropriate positions. How would you ensure that only the 12 Glu in Factor IX that are normally converted to Gla and not just all Glu (Limit 5-6 senetnces)?arrow_forwardIs the Aminoacyl tRNA synthetases in human cells specialized or non specialized? Explain.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_forward
- 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 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_forwardIn 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?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 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_forward
- 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. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning.arrow_forwardKnowing that the genetic code is almost universal, a scientist uses molecular biological methods to insert the human β-globin gene (Shown in Figure 17.11) into bacterial cells, hoping the cells will express it and synthesize functional β-globin protein. Instead, the protein produced is nonfunctional and is found to contain many fewer amino acids than does β-globin made by a eukaryotic cell. Explain why.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
- The protein Xpot transports tRNAs out of the nucleus so that they can be aminoacylated in the cytosol. (a) What tRNA structural features is Xpot likely to recognize? (b) How does Xpot distinguish mature tRNAs from pre-tRNAs?arrow_forwardOrnithine is structurally similar to lysine except ornithine’s side chain is one methylene group shorter than that of lysine. Attempts to chemically synthesize and isolate ornithinyl-tRNA proved unsuccessful. Propose a mechanistic explanation. (Hint: Six-membered rings are more stable than sevenmembered rings.)arrow_forwardAminoacyl-tRNA synthetases are the only component of gene expression that decodes the genetic code. Explain.arrow_forward
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