Bio 102 Practice Problems Genetic Code and Mutation

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6. A tRNA in a bacterial cell contains the anticodon 5’GUU3’. a. During the ‘charging’ reaction, what amino acid should be covalently linked to this tRNA molecule? b. If this same tRNA with the same anticodon was in a mouse brain cell, should the same amino acid be attached? Please explain. 7. Fruit flies (Drosophila) normally have bright red eyes. However, the red color that you see is really a combination of an orange pigment produced by one enzyme and a brown pigment produced by a second enzyme, as shown at right. a. What would be the genotype and phenotype of a purebreeding fruit fly carrying a nonsense mutation in gene A, assuming gene B functions normally? b. What would be the genotype and phenotype of a purebreeding fruit fly carrying a nonsense mutation in gene B, assuming gene A functions normally? c. What would be the genotype and phenotype of the F 1 offspring resulting from a mating between these two flies? d. Give the phenotypes and expected ratios of the F 2 offspring resulting from a mating between two of the F 1 flies. 8. A particular strain of Salmonella typhimurium is his − because a TAC codon was mutated to a stop codon. a. What would have been the anticodon sequence of the tRNA that would have recognized the original codon? b. What mutation might have occurred to produce the his − strain? c. What is the term for this type of mutation? d. Is there a different mutation that would have produced the same result?
9. The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein is a chloride (Cl - ) facilitated transporter made up of 1480 amino acids and whose gene is located on the long arm of chromosome 7. In healthy humans, the protein is found in the plasma membranes of the cells that line the lungs, allowing the movement of Cl - . In people with cystic fibrosis, no functional CFTR is made. a. Do you expect cystic fibrosis to be inherited in a dominant or recessive fashion? Autosomal or sexlinked? b. The CFTR gene is approximately 82,500 bp long. However, CFTR mRNA isolated from the cytoplasm is only 6,500 nucleotides in length. Please explain what happened to the missing 76,000 bp. c. A variety of mutations can lead to a defective CFTR protein and the disease. For each listed mutation, describe why this leads to a nonfunctional protein. Insertion of a U nucleotide at position 3905. Codon 542 is changed from GGA to UGA. A deletion of amino acid 508 means that the CFTR protein never leaves the Golgi. 10. The beak of the rare purple-beaked gooney bird is purple because of two enzymes encoded by two separate genes. Enzyme A, the product of Gene A, converts a white molecule into a red pigment. Enzyme B, the product of Gene B, then converts the red pigment into a purple pigment. The recessive alleles of these two genes produce non-functional enzymes. a. What would be the phenotype of an AAbb gooney bird? Of an aaBB bird? b. In a cross between two AaBb gooney birds, what offspring phenotypes would you expect, and what fraction of the offspring would show each phenotype? 11. The year is 2015, and our first manned mission to Mars has just returned with samples of bacteria-like organisms that live in the Martian soil. Chemical analysis shows that they contain nucleic acid—dubbed “MNA” (Martian nucleic acid)—fairly similar to earthly DNA. a. MNA is double-stranded but is made up of six different nucleotides, none of which appear in earthly DNA. The table below shows the amount of each nucleotide in MNA. Based on this analysis, what are the base-pairing rules? percent of all nucleotide nucleotides in MNA Thioguanine (T) 24.3 Orotidine (O) 9.8 Methylcytidine (M) 15.5 Aminoinosine (A) 10.2 Xanthine (X) 25.5 Tetrahydrouridine (U) 14.7 b. If Martian proteins were composed of the same 20 amino acids used in earthly proteins, what would be the smallest number of MNA bases that could make up a Martian codon? Explain. c. The bases in MNA are all deoxyribonucleotides. Methylcytidine is a pyrimidine. Sketch a methylcytidine nucleotide.
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Bio 102 Practice Problems Genetic Code and Mutation

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