Genetics - Analysis and Principles

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Quiz 13 :

Translation of Mrna

Quiz 13 :

Translation of Mrna

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Polypeptides can be translated in vitro. Would a bacterial mRNA be translated in vitro by eukaryotic ribosomes Would a eukaryotic mRNA be translated in vitro by bacterial ribosomes Why or why not
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Basically initiation of translation between bacteria and eukaryotes are different due to the lack of cap structure at 5' of mRNA in bacteria, so the translation is not possible where as eukaryotic mRNA lacks very important segment called Shine Dalgarno sequence at 5' end, so it is not functional in bacteria system.

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An experimenter has a chemical reagent that modifies threonine to another amino acid. Following the protocol described in Figure 13.11, an mRNA is made composed of 50% C and 50% A. The amino acid composition of the resultant polypeptides is 12.5% lysine, 12.5% asparagine, 25% serine, 12.5% glutamine, 12.5% histidine, and 25% proline. One of the amino acids present in this polypeptide is due to the modification of threonine. Which amino acid is it Based on the structure of the amino acid side chains, explain how the structure of threonine has been modified.
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The amino acid present in the polypeptide is due to changing of threonine in to serine. Based on the structure of amino acids, the threonine was modified due the occurrence of demethylation. In other words, the methyl group has been replaced with hydrogen.

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Which events during translation involve molecular recognition of a nucleotide base sequence within RNA Which events involve recognition between different protein molecules
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img

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The wobble rules for tRNA-mRNA pairing are shown in Figure 13.12. If we assume that the tRNAs do not contain modified bases, what is the minimum number of tRNAs needed to efficiently recognize the codons for the following types of amino acids A. Leucine B. Methionine C. Serine FIGURE 13.12 Wobble position and base-pairing rules. (a) The wobble position occurs at the third base in the mRNA codon and the corresponding base in the anticodon. (b) The revised wobble rules are slightly different from those originally proposed by Crick. The standard bases found in RNA are G, C, A, and U. In addition, the structures of bases in tRNAs may be modified. Some modified bases that may occur in the wobble position in tRNA are I = inosine; xm 5 s 2 U = 5-methyl-2-thiouridine; xm 5 Um = 5-methyl-2 - O -methyluridine; Um = 2 - O -methyluridine; xm 5 U = 5-methyluridine; xo 5 U = 5-hydroxyuridine; k 2 C = lysidine (a cytosine derivative). img
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According to the adaptor hypothesis, are the following statements true or false
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If a tRNA molecule carries a glutamic acid, what are the two possible anticodon sequences that it could contain Be specific about the 5 and 3 ends.
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How many different sequences of mRNA could encode a peptide with the sequence proline-glycine-methionine-serine
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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 tRNA Trp gene would encode a tRNA with the anticodon 3 -ACC-5 . A mutation could 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 tRNA Trp Does the enzyme primarily recognize the anticodon or not
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The technique of Western blotting can be used to detect proteins that are translated from a particular mRNA. This method is described in Chapter 20 and also in experimental question E5. Let's suppose a researcher was interested in the effects of mutations on the expression of a protein-encoding gene that encodes a protein we will call protein X. This protein is expressed in skin cells and contains 572 amino acids. Its molecular mass is approximately 68,600 Da, or 68.6 kDa. Make a drawing that shows the expected results of a Western blot using proteins isolated from the skin cells obtained from the following individuals: Lane 1: A normal individual Lane 2: An individual who is homozygous for a deletion, which removes the promoter for this gene Lane 3: An individual who is heterozygous in which one gene is normal and the other gene has a mutation that introduces an early stop codon at codon 421 Lane 4: An individual who is homozygous for a mutation that introduces an early stop codon at codon 421 Lane 5: An individual who is homozygous for a mutation that changes codon 198 from a valine codon into a leucine codon Question E5 Chapter 20 describes a blotting method known as Western blotting that can be used to detect the production of a polypeptide that is translated from a particular mRNA. In this method, a protein is detected with an antibody that specifically recognizes and binds to its amino acid sequence. The antibody acts as a probe to detect the presence of the protein. In a Western blotting experiment, a mixture of cellular proteins is separated using gel electrophoresis according to their molecular masses. After the antibody has bound to the protein of interest within a blot of a gel, the protein is visualized as a dark band. For example, an antibody that recognizes the -globin polypeptide could be used to specifically detect the -globin polypeptide in a blot. As shown here, the method of Western blotting can be used to determine the amount and relative size of a particular protein that is produced in a given cell type. img Lane 1 is a sample of proteins isolated from normal red blood cells. Lane 2 is a sample of proteins isolated from kidney cells. Kidney cells do not produce globin. Lane 3 is a sample of proteins isolated from red blood cells from a patient with -thalassemia. This patient is homozygous for a mutation that results in the shortening of the -globin polypeptide. Now here is the question. A protein called troponin contains 334 amino acids. Because each amino acid weighs 120 daltons (Da) (on average), the molecular mass of this protein is about 40,000 Da, or 40 kDa. Troponin functions in muscle cells, and it is not expressed in nerve cells. Draw the expected results of a Western blot for the following samples: Lane 1: Proteins isolated from muscle cells Lane 2: Proteins isolated from nerve cells Lane 3: Proteins isolated from the muscle cells of an individual who is homozygous for a mutation that introduces a stop codon at codon 177
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. Figure 13.21 shows an electron micrograph of a bacterial gene as it is being transcribed and translated. In this figure, label the 5 and 3 ends of the DNA and RNA strands. Place an arrow where you think the start codons are found in the mRNA transcripts.
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A tRNA has an anticodon sequence 3 -GGU-5 . What amino acid does it carry
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An mRNA has the following sequence: 5 -GGCGAUGGGCAAUAAACCGGGCCAGUAAGC-3 Identify the start codon and determine the complete amino acid sequence that would be translated from this mRNA.
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What does it mean when we say that the genetic code is degenerate Discuss the universality of the genetic code.
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With regard to the experiment described in Figure 13.11, answer the following questions: A. Why was a polyUG mRNA template used B. Would you radiolabel the cysteine with the isotope 14C or 35S Explain your choice. C. What would be the expected results if the experiment was followed in the same way except that a polyGC template was used Note: A polyGC template could contain two different alanine codons (GCC and GCG), but it could not contain any cysteine codons.
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Chapter 20 describes a blotting method known as Western blotting that can be used to detect the production of a polypeptide that is translated from a particular mRNA. In this method, a protein is detected with an antibody that specifically recognizes and binds to its amino acid sequence. The antibody acts as a probe to detect the presence of the protein. In a Western blotting experiment, a mixture of cellular proteins is separated using gel electrophoresis according to their molecular masses. After the antibody has bound to the protein of interest within a blot of a gel, the protein is visualized as a dark band. For example, an antibody that recognizes the -globin polypeptide could be used to specifically detect the -globin polypeptide in a blot. As shown here, the method of Western blotting can be used to determine the amount and relative size of a particular protein that is produced in a given cell type. img Lane 1 is a sample of proteins isolated from normal red blood cells. Lane 2 is a sample of proteins isolated from kidney cells. Kidney cells do not produce globin. Lane 3 is a sample of proteins isolated from red blood cells from a patient with -thalassemia. This patient is homozygous for a mutation that results in the shortening of the -globin polypeptide. Now here is the question. A protein called troponin contains 334 amino acids. Because each amino acid weighs 120 daltons (Da) (on average), the molecular mass of this protein is about 40,000 Da, or 40 kDa. Troponin functions in muscle cells, and it is not expressed in nerve cells. Draw the expected results of a Western blot for the following samples: Lane 1: Proteins isolated from muscle cells Lane 2: Proteins isolated from nerve cells Lane 3: Proteins isolated from the muscle cells of an individual who is homozygous for a mutation that introduces a stop codon at codon 177
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In the experiment of Figure 13.7, what would be the predicted amounts of amino acids incorporated into polypeptides if the RNA was a random polymer containing 50% C and 50% G FIGURE 13.7 Elucidation of the genetic code. Starting material: A cell-free translation system that can synthesize polypeptides if mRNA and amino acids are added. The translation system contained ribosomes, tRNAs, and other factors required for translation. These other factors included enzymes that attach amino acids to tRNA molecules. img img
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The covalent attachment of an amino acid to a tRNA is an ender-gonic reaction. In other words, it requires an input of energy for the reaction to proceed. Where does the energy come from to attach amino acids to tRNA molecules
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Discuss and make a list of the similarities and differences in the events that occur during the initiation, elongation, and termination stages of transcription (see Chapter 12) and translation discussed in this chapter.
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Discuss why you think the ribosome needs to contain so many proteins and rRNA molecules. Does it seem like a waste of cellular energy to make such a large structure so that translation can occur
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Discuss how the elucidation of the structure of the ribosome can help us to understand its function.
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