Chapter 27 Testbank
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Chapter 27 Testbank

Course Number: BHC 3023, Spring 2010

College/University: USF

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Chapter 27 Protein Metabolism Multiple Choice Questions 1. The genetic code Page: 1069 Difficulty: 2 Ans: C A certain bacterial mRNA is known to represent only one gene and to contain about 800 nucleotides. If you assume that the average amino acid residue contributes 110 to the peptide molecular weight, the largest polypeptide that this mRNA could code for would have a molecular weight of about: A) B) C) D) E)...

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27 Chapter Protein Metabolism Multiple Choice Questions 1. The genetic code Page: 1069 Difficulty: 2 Register to View AnswerA certain bacterial mRNA is known to represent only one gene and to contain about 800 nucleotides. If you assume that the average amino acid residue contributes 110 to the peptide molecular weight, the largest polypeptide that this mRNA could code for would have a molecular weight of about: A) B) C) D) E) 800. 5,000. 30,000. 80,000. An upper limit cannot be determined from the data given. 2. The genetic code Page: 1069 Difficulty: 2 Register to View AnswerAssuming that the average amino acid residue contributes 110 to the peptide molecular weight, what will be the minimum length of the mRNA encoding a protein of molecular weight 50,000? A) B) C) D) E) 133 nucleotides 460 nucleotides 1,400 nucleotides 5,000 nucleotides A minimum length cannot be determined from the data given. 3. The genetic code Pages: 1070-1074 Difficulty: 3 Register to View AnswerWhich of the following are features of the "wobble" hypothesis? A) B) C) D) E) A naturally occurring tRNA exists in yeast that can read both arginine and lysine codons. A tRNA can recognize only one codon. Some tRNAs can recognize codons that specify two different amino acids, if both are nonpolar. The "wobble" occurs only in the first base of the anticodon. The third base in a codon always forms a normal Watson-Crick base pair. 4. The genetic code Page: 1069 Difficulty: 2 Register to View AnswerWhich one of the following is true about the genetic code? A) B) C) D) All codons recognized by a given tRNA encode different amino acids. It is absolutely identical in all living things. Several different codons may encode the same amino acid. The base in the middle position of the tRNA anticodon sometimes permits "wobble" base pairing with 2 or 3 different codons. E) The first position of the tRNA anticodon is always adenosine. 82 Chapter 27 Protein Metabolism 5. Protein synthesis Pages: 1076-1077 Difficulty: 1 Register to View AnswerWhich one of the following statements about ribosomes is true? A) The large subunit contains rRNA molecules, the small subunit does not. B) The RNA in ribosomes plays a structural, not catalytic, role. C) There are about 25 of them in an E. coli cell. D) There are two major subunits, each with multiple proteins. E) They are relatively small, with molecular weights less than 10,000. 6. Protein synthesis Pages: 1079-1080 Difficulty: 2 Register to View AnswerWhich of the following statements about tRNA molecules is false? A) A, C, G, and U are the only bases present in the molecule. B) Although composed of a single strand of RNA, each molecule contains several short, doublehelical regions. C) Any given tRNA will accept only one specific amino acid. D) The amino acid attachment is always to an A nucleotide at the 3' end of the molecule. E) There is at least one tRNA for each of the 20 amino acids. 7. Protein synthesis Page: 1080 Difficulty: 2 Register to View AnswerWhich of the following statements about the tRNA that normally accepts phenylalanine is false? (mRNA codons for phenylalanine are UUU and UUC.) A) It interacts specifically with the Phe synthetase. B) It will accept only the amino acid phenylalanine. C) Its molecular weight is about 25,000. D) Phenylalanine can be specifically attached to an --OH group at the 3' end. E) The tRNA must contain the sequence UUU. 8. Protein synthesis Page: 1081 Difficulty: 2 Register to View AnswerWhich of the following is not true of tRNA molecules? A) The 3'-terminal sequence is --CCA. B) C) D) E) Their anticodons are complementary to the triplet codon in the mRNA. They contain more than four different bases. They contain several short regions of double helix. With the right enzyme, any given tRNA molecule will accept any of the 20 amino acids. 9. Protein synthesis Page: 1081 Difficulty: 2 Register to View AnswerAminoacyl-tRNA synthetases (amino acid activating enzymes): A) B) C) D) "recognize" specific tRNA molecules and specific amino acids. in conjunction with another enzyme attach the amino acid to the tRNA. interact directly with free ribosomes. occur in multiple forms for each amino acid. Chapter 27 Protein Metabolism 83 E) require GTP to activate the amino acid. 10. Protein synthesis Pages: 1081-1083 Difficulty: 2 In E. coli, aminoacyl-tRNA synthetases: A) B) C) D) E) Register to View Answer activate amino acids in 12 steps. are amino acidspecific; there is at least one enzyme specific for each amino acid. fall into two classes, each of which attaches amino acids to different ends of the tRNA. have no proofreading activities. require a tRNA, an amino acid, and GTP as substrates. 11. Protein synthesis Pages: 1081-1084 Difficulty: 2 Register to View AnswerWhich of the following statements about aminoacyl-tRNA synthetases is false? A) Some of the enzymes have an editing/proofreading capability. B) The enzyme attaches an amino acid to the 3' end of a tRNA. C) The enzyme splits ATP to AMP + PPi. D) The enzyme will use any tRNA species, but is highly specific for a given amino acid. E) There is a different synthetase for every amino acid. 12. Protein synthesis Pages: 1081-1082 Difficulty: 2 Register to View AnswerThe enzyme that attaches an amino acid to a tRNA (aminoacyl-tRNA synthetase): A) always recognizes only one specific tRNA. B) attaches a specific amino acid to any available tRNA species. C) attaches the amino acid at the 5' end of the tRNA. D) catalyzes formation of an ester bond. E) splits ATP to ADP + Pi. 13. Protein synthesis Pages: 1081-1082 Difficulty: 2 Register to View AnswerIn the "activation" of an amino acid for protein synthesis: A) leucine can be attached to tRNAPhe by the aminoacyl-tRNA synthetase specific for leucine. B) methionine is first formylated, then attached to a specific tRNA. C) the amino acid is attached to the 5' end of the tRNA through a phosphodiester bond. D) there is at least one specific activating enzyme and one specific tRNA for each amino acid. E) two separate enzymes are required, one to form the aminoacyl adenylate, the other to attach the amino acid to the tRNA. 14. Protein synthesis Page: 1088 Difficulty: 1 Register to View AnswerWhich of the following is (are) true for protein synthesis in eukaryotes? A) All proteins are initially synthesized with methionine at their C-terminus. B) All proteins are initially synthesized with methionine at their N-terminus. C) All proteins are initially synthesized with tryptophan at their C-terminus. 84 Chapter 27 Protein Metabolism D) All proteins are initially synthesized with a multiple of 3 amino acids in their sequence. E) None of the above. 15. Protein synthesis Pages: 1088-1089 Difficulty: 2 Register to View AnswerFormation of the ribosomal initiation complex for bacterial protein synthesis does not require: A) B) C) D) E) EF-Tu. formylmethionyl tRNAfMet. GTP. initiation factor 2 (IF-2). mRNA. 16. Protein synthesis Page: 1091 Difficulty: 2 Register to View AnswerIn bacteria the elongation stage of protein synthesis does not involve: A) B) C) D) E) aminoacyl-tRNAs. EF-Tu. GTP. IF-2. peptidyl transferase. 17. Protein synthesis Page: 1091 Difficulty: 2 Register to View AnswerWhich one of the following statements about the elongation phase of protein synthesis is true? A) B) C) D) At least five high-energy phosphoryl groups are expended for each peptide bond formed. During elongation, incoming aminoacylated tRNAs are first bound in the P site. Elongation factor EF-Tu facilitates translocation. Peptidyl transferase catalyzes the attack of the carboxyl group of the incoming amino acid on an ester linkage in the nascent polypeptide. E) Peptidyl transferase is a ribozyme. 18. Protein synthesis Pages: 1092-1093 Difficulty: 2 Register to View AnswerWhich of the following statements about bacterial mRNA is true? A) A ribosome usually initiates translation near the end of the mRNA that is synthesized last. B) An mRNA is never degraded but is passed on to the daughter cells at cell division. C) During polypeptide synthesis, ribosomes move along the mRNA in the direction 5' 3'. D) Ribosomes cannot initiate internally in a polycistronic transcript. E) The codon signaling peptide termination is located in the mRNA near its 5' end. 19. Protein synthesis Pages: 1092-1093 Bacterial ribosomes: Difficulty: 2 Register to View Answer A) bind tightly to specific regions of DNA, forming polysomes. B) contain at least one catalytic RNA molecule (ribozyme). Chapter 27 Protein Metabolism 85 C) contain three species of RNA and five different proteins. D) have specific, different binding sites for each of the 20 tRNAs. E) require puromycin for normal function. 20. Protein synthesis Page: 1096 Difficulty: 1 Register to View AnswerThe large structure consisting of an mRNA molecule being translated by multiple copies of the macromolecular complexes that carry out protein synthesis is called a: A) B) C) D) E) lysosome. polysome. proteosome. ribosome. synthosome. 21. Protein synthesis Page: 1093 Difficulty: 3 Register to View AnswerIt is possible to convert the Cys that is a part of Cys-tRNACys to Ala by a catalytic reduction. If the resulting Ala-tRNACys were added to a mixture of (1) ribosomes, (2) all the other tRNAs and amino acids, (3) all of the cofactors and enzymes needed to make protein in vitro, and (4) mRNA for hemoglobin, where in the newly synthesized hemoglobin would the Ala from Ala-tRNACys be incorporated? A) B) C) D) E) Nowhere; this is the equivalent of a nonsense mutation Wherever Ala normally occurs Wherever Cys normally occurs Wherever either Ala or Cys normally occurs Wherever the dipeptide Ala-Cys normally occurs 22. Protein synthesis Page: 1095 Difficulty: 3 Register to View AnswerApproximately how many NTPs must be converted to NDPs to incorporate one amino acid into a protein? A) B) C) D) E) 0 1 2 4 8 23. Protein synthesis Pages: 1088-1089 Difficulty: 2 Register to View AnswerWhich one of the following antibiotics does not function by interfering with the translational process? A) B) C) D) E) Chloramphenicol Cycloheximide Penicillin Puromycin Streptomycin 86 Chapter 27 Protein Metabolism 24. Protein targeting and degradation Page: 1101 Difficulty: 2 Register to View AnswerWhich of the following is true about the sorting pathway for proteins destined for incorporation into lysosomes or the plasma membrane of eukaryotic cells? A) B) C) D) Binding of SRP to the signal peptide and the ribosome temporarily accelerates protein synthesis. The newly synthesized polypeptides include a signal peptide at their carboxyl termini. The signal peptide is cleaved off inside the mitochondria by signal peptidase. The signal recognition particle (SRP) binds to the signal peptide soon after it appears outside the ribosome. E) The signal sequence is added to the polypeptide in a posttranslational modification reaction. 25. Protein targeting and degradation Pages: 1101-1102 Difficulty: 2 Register to View AnswerGlycosylation of proteins inside the endoplasmic reticulum does not involve: A) B) C) D) a His residue on the protein. an Asn residue on the protein. dolichol phosphate. glucose. E) N-acetylglucosamine. 26. Protein targeting and degradation Page: 1102 Difficulty: 2 Register to View AnswerPosttranslational glycosylation of proteins is inhibited specifically by: A) B) C) D) E) chloramphenicol. cycloheximide. puromycin. streptomycin. tunicamycin. 27. Protein targeting and degradation Page: 1104 Difficulty: 2 Register to View AnswerThe signal sequences that direct proteins to the nucleus are: A) B) C) D) E) always at the amino terminus of the targeted protein. cleaved after the protein arrives in the nucleus. glycosyl moieties containing mannose 6-phosphate residues. not located at the ends of the peptide, but in its interior. the same as those that direct certain proteins to lysosomes. Chapter 27 Protein Metabolism 87 28. Protein targeting and degradation Pages: 1104-1106 Difficulty: 3 Register to View AnswerThe pathway for polypeptides exported from E. coli includes the following steps, which occur in what order for correct export? 1. 2. 3. 4. A) B) C) D) E) 1, 2, 3, 4 1, 2, 4, 3 2, 1, 4, 3 2, 3, 1, 4 3, 1, 4, 2 A chaperone, SecA, binds to the polypeptide. A chaperone, SecB, binds to the polypeptide. ATP is hydrolyzed by SecA. SecA pushes 20 amino acids of the polypeptide into the translocation complex. 29. Protein targeting and degradation Pages: 1108-1109 Difficulty: 3 Register to View AnswerUbiquitin-mediated protein degradation is a complex process, and many of the signals remain unknown. One known signal involves recognition of amino acids in a processed protein that are either stabilizing (Ala, Gly, Met, Ser, etc.) or destabilizing (Arg, Asp, Leu, Lys, Phe, etc.), and are located at: A) B) C) D) E) a helix-turn-helix motif in the protein. a lysine-containing target sequence in the protein. a zinc finger structure in the protein. the amino-terminus of the protein. the carboxy-terminus of the protein. Short Answer Questions 30. The genetic code Pages: 1066-1067 Difficulty: 2 Outline one of the experimental methods providing evidence that the genetic code was a triplet code. Ans: When one or two nucleotides were added to or deleted from a gene, the resulting mRNA produced a protein with a different amino acid sequence after the deletion or insertion. When three nucleotides were added or deleted, the resulting protein had a normal sequence except for the insertion or deletion of a single amino acid residue. 31. The genetic code Pages: 1066-1068 Difficulty: 3 Describe, succinctly, two ways in which synthetic polynucleotides were used in solving the genetic code (you need not describe how the synthetic polynucleotides were made). Ans: (1) When synthetic polymers of only one nucleotide were used as mRNA in vitro, only one of the 20 amino acids was converted into protein. For example, poly(U) (containing only the codon UUU) directed the synthesis of polyphenylalanine, showing that UUU encodes Phe. (2) Trinucleotides of known sequence were used to stimulate aminoacyl-tRNA binding to ribosomes. Because only that aminoacyl-tRNA whose anticodon matched the trinucleotide "mRNA" was bound, the coding specificity of each sequence of three bases could be determined by determining which of 88 Chapter 27 Protein Metabolism the 20 aminoacyl-tRNAs bound. (3) Random polymers of RNA containing known ratios of nucleotides (for example, 70% A and 30% T) generate only certain codons in predictable ratios. The identities and ratios of the amino acids specified by such polymers provided important clues that helped solve the genetic code. (4) Additional assignments were made possible using synthetic oligonucleotides containing repeats of specific two, three, or four base pair sequences. 32. The genetic code Page: 1069 Difficulty: 3 You have isolated a fragment of viral DNA that totally encodes at least two proteins, 120 and 80 amino acids long. The DNA fragment is 400 base pairs long. (a) Why might you consider this unusual? (b) You sequence the two proteins and find no sequence homology. Propose a model to account for these findings. Ans: (a) Two distinct proteins of these sizes should require mRNAs of 360 and 240 base pairs because each amino acid residue requires 3 base pairs to code for it. (b) No homology means that the smaller protein cannot be derived from the larger by proteolysis; if it were, there would be 80 amino acid residues of identical sequence in the two proteins. One possible explanation is that the two genes coding for these proteins overlap and are read in different reading frames. 33. The genetic code Page: 1069 Difficulty: 2 Consider the following hypothetical short mRNA; what would be the sequence of the protein produced if this were translated in an E. coli cell? 5'-AUAGGAGGUUUGACCUAUGCCUCGUUUAUAGCC-3' Ans: N-met-pro-arg-leu-C 34. The genetic code Page: 1069 Difficulty: 2 The template strand of a segment of double-stranded DNA contains the sequence: (5')CTT TGA TAA GGA TAG CCC TTC (a) What is the base sequence of the mRNA that can be transcribed from this strand? (b) What amino acid sequence could be coded by the mRNA base sequence in (a), using only the first reading frame starting at the end? 5' (Refer to Fig. 27-7, p. 1069.) (c) Suppose the other (complementary) strand is used as a template for transcription. What is the amino acid sequence of the resulting peptide, again starting from the 5' end and using only the first reading frame? Ans: (a) (5')GAA GGG CUA UCC UUA UCA AAG(3') (b) Glu-Gly-Leu-Ser-Leu-Ser-Lys (c) The codons translate to Leu-Stop-Stop. No peptide would be produced because of the stop codons. (See also Fig. 27-7, p. 1069.) 35. The genetic code Page: 1069 Difficulty: 3 Describe the possible outcomes that could occur because of a single base change in an mRNA Ans: The most likely result is a single amino acid change in the encoded protein, when a codon is Chapter 27 Protein Metabolism 89 altered to one of another amino acid. However, some nucleotide changes will be "silent" and not change the protein, if the altered codon still specifies the original amino acid. Conversion to a nonsense codon will result in a truncated polypeptide, while alteration of the normal stop codon to a "sense" codon will result in a lengthened protein. Alternation of the initiation codon may result in the total failure to translate, and result in no protein product. Changes in mRNA sequence outside the protein-coding region may affect translational efficiency, splicing, or mRNA turnover rates. 36. The genetic code Page: 1069 Difficulty: 3 The following sequence of four amino acids occurred in the structure of a polypeptide found in a wild-type organism: Leu-Ser-Ile-Arg. Several mutants were isolated, each of which carried a single base pair change in the region of DNA that coded for this amino acid sequence. Their corresponding amino acid sequences are: Mutant 1 2 3 4 5 MET-Ser-Ile-Arg Leu-TRP-Ile-Arg Leu-Ser-ARG-Arg Leu-Ser-Ile-PRO Leu-Ser-Ile-TRP What was the nucleotide sequence of the region of mRNA that coded for the amino acid sequence in the wild-type organism? (Refer to Fig. 27-7, p. 1069.) Ans: (5')C or (5')U UG UCG AUA CGG 37. The genetic code Pages: 1070-1074 Difficulty: 2 In protein synthesis, 61 codons specify the 20 amino acids. Base pairing between the codon and the tRNA anticodon assures that the correct amino acid will be inserted into the nascent polypeptide chain. Why, then, does the cell require only 32 different tRNAs to recognize 61 different codons? Ans: Certain tRNAs have the unusual nucleotide inosinate in the first anticodon position. Because inosinate can base-pair with A, U, or C, a tRNA containing hypoxanthine can recognize three different codons. In each recognized codon, there is a standard anticodon-codon base pair with the first two bases of the codon; "wobble" in the third base pair allows one tRNA to read three different codons. Similarly, tRNAs with U or G in the first anticodon position also exhibit a wobble effect that permits pairing with two different codons. 38. Protein synthesis Pages: 1076-1079 Difficulty: 1 Indicate whether the following statements are true (T) or false (F). ___A ribosome is the complex within which protein synthesis occurs. ___Ribosomes contain many separate proteins. ___The three ribosomal RNAs in a bacterial ribosome are distributed in three separate, large ribosomal subunits. ___There are four binding sites for aminoacyl-tRNAs on a ribosome. Register to View AnswerT; F; F 90 Chapter 27 Protein Metabolism 39. Protein synthesis Pages: 1081-1083 Difficulty: 2 The process of charging tRNAs with their cognate amino acids involves multiple proofreading steps to increase the overall fidelity. Briefly describe these steps. Ans: There are two main stages of selection: 1) the synthetase strongly favors activation of the correct amino acid to become aminoacyl-AMP (incorrect amino acids are very poorly activated) and 2) when the correct uncharged tRNA is bound to the enzyme, only the correct aminoacyl-AMP is tolerated in the "proofreading" active site (incorrect aminoacyl-AMPs, though they may become bound, are rapidly hydrolyzed). In addition, for most synthetases, if their tRNA does manage to become acylated by the wrong amino acid, that product is also rapidly hydrolyzed. 40. Protein synthesis Pages: 1083-1084 Difficulty: 2 The recognition of an amino acid by its cognate aminoacyl-tRNA synthetase is said to involve a "second genetic code." What is meant by this? Ans: Each of the 20 amino acids has a unique synthetase, but many have multiple cognate tRNAs that must be charged (aminoacylated). The "second code" refers to features common to all tRNAs that carry the same amino acid, making them specifically recognizable by the correct synthetase. These features occur at different places in different tRNA classes, and may be as simple as a single G-U basepair, or require ten or more specific nucleotides throughout the sequence. (See Fig. 27-21, p. 1083.) 41. Protein synthesis Page: 1088 Difficulty: 3 In 1961, Howard Dintzis carried out an experiment that defined the direction of polypeptide chain growth during protein synthesis in cells. The experiment involved the analysis of hemoglobin molecules that were being synthesized in reticulocytes in the presence of radioactive amino acids. Describe the analysis and how it demonstrated the direction of chain growth. Ans: In the experiment, only completed polypeptides were isolated and analyzed for the amount of radioactivity in different regions. The greatest radioactivity should be located in the region farthest from the initiation point and the least radioactivity in the region closest to the initiation point. The opposite is true for the termination point. The analysis showed that polypeptide synthesis was initiated at the amino terminus and terminated at the carboxyl terminus. 42. Protein synthesis Pages: 1088-1090 Difficulty: 3 A given mRNA sequence might be translated in any of three reading frames. Describe how prokaryotes and eukaryotes determine the correct reading frame. Ans: In prokaryotes, the Shine-Dalgarno sequence in the mRNA base-pairs with a complementary sequence in the 16S RNA of the ribosome; this positions the correct start codon (AUG) on the 30S ribosomal subunit. Thus, the initiating AUG is distinguished by its proximity to the Shine-Dalgarno sequence. In eukaryotes, the initiating AUG codon is the first AUG that the ribosome encounters as it scans the mRNA from its 5' end. In both cases the initiating AUG also sets the correct reading frame. Chapter 27 Protein Metabolism 91 43. Protein synthesis Pages: 1088-1095 Difficulty: 1 Match the factor or enzyme at the right with the stage(s) of protein synthesis at which it acts. If a factor or enzyme participates in two stages of protein synthesis, indicate both of them. ___ ___ ___ ___ Amino acid activation Initiation Elongation Termination (a) RF1 (b) EF-Tu (c) aminoacyl-tRNA (d) Shine-Dalgarno sequence Register to View Answerd; b; a 44. Protein synthesis Pages: 1088-1095 Difficulty: 2 Indicate whether each of the following statements is true (T) or false (F). ___Assembly of a complete ribosome onto an mRNA requires ATP hydrolysis. ___Aminoacylation or "charging" of tRNA requires the formation of an aminoacyl-AMP intermediate. ___Aminoacyl-tRNA binding to the A site of the ribosome requires the accessory factor EF-G and GTP hydrolysis. ___Translocation of a growing polypeptide from the A to the P site on the ribosome requires EFG and GTP hydrolysis. ___Termination of translation requires release factors, but no NTP hydrolysis. Register to View AnswerT; F; T; T 45. Protein synthesis Pages: 1088-1095 Difficulty: 3 Briefly describe the role of the following components in bacterial protein synthesis. (a) Initiation factor 2 (IF-2) (b) 16S RNA (c) Peptidyl transferase (d) Release factors (e) Elongation factor G (EF-G) (f) N10-formyltetrahydrofolate (g) ATP (h) tRNAfMet Ans: (a) IF-2 is a protein factor that, when bound to GTP, brings the fMet-tRNAfMet to the initiation complex. (b) 16S RNA is a component of the small (30S) subunit. It contains a sequence complementary to the Shine-Dalgarno sequence in the mRNA, and helps to line up the mRNA initiation AUG codon on the ribosome. (c) Peptidyl transferase is a ribozyme in the 50S ribosomal subunit. It catalyzes formation of each peptide bond as the ribosome moves along the mRNA. (d) Release factors are proteins that bring about the release of the finished polypeptide when the ribosome encounters a termination codon in the mRNA. (e) EF-G participates in the translocation of the ribosome down the mRNA by one codon after each peptide bond is formed. (f) N10-formyltetrahydrofolate is the cofactor that donates a methyl group in the conversion of tRNA-bound Met to fMet. (g) ATP is the substrate for aminoacyl-tRNA synthetases; it donates an AMP residue in the formation of aminoacyl adenylate, which donates the aminoacyl group to tRNA. (h) tRNAfMet is the 92 Chapter 27 Protein Metabolism transfer RNA that initiates protein synthesis by inserting the first amino acid (fMet) in every prokaryotic protein. 46. Protein synthesis Pages: 1088-1095 Difficulty: 2 Number the following steps in the proper order with regard to protein synthesis. ___ Aminoacyl-tRNA binds to the A site. ___ Deacylated tRNA is released from ribosome. ___ Peptide bond formation shifts the growing peptide from the P to the A site. ___ The 50S subunit binds to the initiation complex of the 30S subunit and mRNA. Ans: 2; 4; 3; 1 47. Protein synthesis Pages: 1088-1096 Difficulty: 2 Indicate whether each of the following statements is true (T) or false (F). ___ Bacterial mRNA is broken down within a few minutes of its formation in E. coli. ___ Bacterial mRNA consists only of the bases that code for amino acids. ___ Polysomes do not necessarily contain mRNA. ___ Bacterial mRNA normally occurs as a double-stranded structure, with one strand containing codons, the other containing anticodons. ___ Bacterial mRNA can be translated while it is still being synthesized. Register to View AnswerF; F; F; T 48. Protein synthesis Pages: 1088-1096 Difficulty: 2 Register to View AnswerRegarding translation in eukaryotes versus that in prokaryotes (bacteria), indicate whether each of the following statements is true (T) or false (F). ___ In eukaryotes the 3' end of the mRNA is associated with the 5' end during initiation whereas in prokaryotes it is not. ___ In prokaryotes it is initiated at an AUG near a Shine-Dalgarno sequence in the mRNA whereas in eukaryotes it is initiated at an AUG near the 3' end of the mRNA. ___ In prokaryotes it is initiated with Met whereas in eukaryotes it is initiated with fMet. ___ In prokaryotes translation and transcription are coupled whereas in eukaryotes they are not. Register to View AnswerF, F, T 49. Protein synthesis Pages: 1091-1094 Difficulty: 2 Polypeptide chain elongation in E. coli occurs by the cyclical repetition of three steps. What are these steps and what cellular components are necessary for each of them to occur? Ans: The three steps are: (1) An aminoacyl-tRNA is brought to the A site by EF-Tu with bound GTP; (2) peptidyl transferase (a ribozyme) catalyzes peptide-bond formation; (3) the ribosome translocates three nucleotides down the mRNA, helped by EF-G (translocase). This shifts the peptidyl-tRNA to the A site and the deacylated tRNA to the E site. Chapter 27 Protein Metabolism 93 50. Protein synthesis Pages: 1091-1092 Difficulty: 2 A new antibiotic was recently discovered that inhibits prokaryotic protein synthesis. In the presence of the antibiotic, protein synthesis can be initiated, but only dipeptides that remain bound to the ribosome are formed. What specific step of protein synthesis is likely to be blocked by this antibiotic? Ans: The antibiotic probably blocks translocation. 51. Protein synthesis Pages: 1096-1098 Difficulty: 2 Following the synthesis of their polypeptide chain, many proteins require further posttranslational modifications before they attain their full biological activity or function. List and describe briefly at least four possible types of modification that can occur. Ans: 1) Amino-terminal modification (N-acetylation or deacetylation), 2) removal of signal sequences used for targeting, 3) side-chain modification (phosphorylation, carboxylation, methylation, etc.), 4) attachment of N-linked (to Asn) or O-linked (to Ser or Thr) oligosaccharide moieties, 5) isoprenylation of Cys side-chains, 6) incorporation of prosthetic groups (heme, biotin, etc.), 7) processing of proenzymes or zymogens, and 8) formation of disulfide crosslinks. 52. Protein synthesis Page: 1094 Difficulty: 3 In no more than three sentences, describe a nonsense suppressor tRNA and how it differs from a normal tRNA. Register to View Answersuppressor tRNA has one or more altered bases in its anticodon, which allows it to base-pair with one of the stop codons. This allows the insertion of an amino acid instead of the chain termination that would normally have occurred at the point of a nonsense (stop) codon. 53. Protein targeting and degradation Pages: 1100-1101 Difficulty: 2 When first synthesized, proinsulin has an additional leader or signal peptide at its amino terminus. This complete molecule is called preproinsulin and the signal peptide is cleaved off to give proinsulin. Briefly, what is the likely function of the signal peptide? Ans: The leader peptide in proinsulin is a signal sequence directing it to the endoplasmic reticulum, from which it enters the Golgi complex and is packaged into a secretory vesicle for secretion by exocytosis. 54. Protein targeting and degradation Page: 1101 Difficulty: 2 Describe the sequence of events between the transcription of an mRNA for a secreted protein and the arrival of that protein in the lumen of the endoplasmic reticulum. Ans: (1) The mRNA forms an initiation complex with a cytoplasmic ribosome and transcription begins. (2) The amino-terminal portion of the nascent chain, containing a signal sequence, binds to an SRP (signal recognition particle), interrupting polypeptide elongation. (3) The SRP-ribosomenascent chain complex binds to the ribosome and SRP receptors on the cytosolic face of the ER; the SRP then dissociates. (4) Chain elongation continues, with the newly synthesized polypeptide crossing into the ER lumen as it grows. (5) The signal sequence is cleaved. 94 Chapter 27 Protein Metabolism 55. Protein targeting and degradation Pages: 1104-1106 Difficulty: 2 What are the stages in targeting of nuclear proteins, and why are the targeting sequences not removed upon arrival of the protein in the nucleus? Ans: In the cytoplasm, where eukaryotic protein synthesis occurs, proteins carrying nuclear localization signal (NLS) sequences are bound by a complex of importin and , which is then bound to a nuclear pore. Ran GTPase mediates translocation of this complex into the nucleus, where importin dissociates from importin , and importin releases the nuclear protein. Importin and are then exported from the nucleus, and available for another cycle of import. The nuclear envelope of higher eukaryotes breaks down at each cell division, distributing the nuclear contents throughout the cell. When the nuclear envelope is reestablished, NLS-carrying proteins can be reimported to fulfill their function. 56. Protein targeting and degradation Pages: 1107-1108 Difficulty: 3 Describe the role of ubiquitin in mediating intracellular protein breakdown. Ans: Ubiquitin, a protein found in all eukaryotic cells, is covalently joined to proteins targeted for degradation. The carboxyl-terminal residue of ubiquitin is first activated by the formation of a thioester with the first enzyme in the pathway in an ATP-dependent reaction. After displacement of the first enzyme by a second, also yielding a thioester link, ubiquitin is finally joined through its carboxyl terminus to a lysine -amino group in the protein to be degraded. The presence of ubiquitin targets the protein for degradation by cellular proteases.

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Chapter 4 The Three-Dimensional Structure of ProteinsMultiple Choice Questions1. Overview of protein structure Pages: 114-115 Difficulty: 1 All of the following are considered "weak" interactions in proteins, except: A) B) C) D) E) hydrogen bonds. hydro
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Chapter 5 Protein FunctionMultiple Choice Questions1. Reversible binding of a protein to a ligand: oxygen-binding proteins Page: 153 Difficulty: 2 The interactions of ligands with proteins: A) B) C) D) E) are relatively nonspecific. are relatively rare
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Chapter 6 EnzymesMultiple Choice Questions1. An introduction to enzymes Pages: 183-184 Difficulty: 1 One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it
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Chapter 7 Carbohydrates and GlycobiologyMultiple Choice Questions1. Monosaccharides and disaccharides Page: 236 Difficulty: 1 To possess optical activity, a compound must be: A) B) C) D) E) a carbohydrate. a hexose. asymmetric. colored. D-glucose.2. Mo
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Chapter 10 LipidsMultiple Choice Questions1. Structural lipids in membranes Pages: 343-345 Difficulty: 2 Which of the following statements concerning fatty acids is correct? A) B) C) D) E) One is the precursor of prostaglandins. Phosphatidic acid is a c
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Chapter 11 Biological Membranes and TransportMultiple Choice Questions1. The composition and architecture of membranes Page: 372 Difficulty: 2 Which one of the following statements about membranes is true? A) B) C) D) E) 2. Most plasma membranes contain
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Chapter 12 BiosignalingMultiple Choice Questions1. Molecular mechanisms of signal transduction Page: 420 Difficulty: 2 Which of the following is not involved in the specificity of signal transduction? A) B) C) D) E) Interactions between receptor and sig
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Chapter 13 Principles of BioenergeticsMultiple Choice Questions1. Bioenergetics and thermodynamics Page: 492 Difficulty: 1 If the G' of the reaction A B is 40 kJ/mol, under standard conditions the reaction: A) is at equilibrium. B) will never reach equi
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Chapter 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate PathwayMultiple Choice Questions1. Glycolysis Page: 528 Difficulty: 2 Glycolysis is the name given to a metabolic pathway occurring in many different cell types. It consists of 11 enzymat
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Chapter 15 Principles of Metabolic RegulationMultiple Choice Questions1. Regulation of metabolic pathways Page: 571 Difficulty: 2 Aside from maintaining the integrity of its hereditary material, the most important general metabolic concern of a cell is:
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Chapter 16 The Citric Acid CycleMultiple Choice Questions1. Production of acetyl-CoA (activated acetate) Page: 617 Difficulty: 2 Which of the following is not true of the reaction catalyzed by the pyruvate dehydrogenase complex? A) B) C) D) E) Biotin pa
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Exam 1 Spring 051. Which of the following amino acids would be most difficult to separatea. b. c. d. e. electrophoretically (at any pH)? lys, val, thr leu, ala, met his, arg, glu leu, lys, asp phe, arg, lys2. Imagine 50mL of 0.1M NaOH is mixed with 51m
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BCH 3023, Fall 2006 Exam 1BCH 3023 Fall Semester, 2006 Exam 1 FORM ANAME _ ID _Bubble in the Test Form Code circle on your scantron with the Form Letter shown above. Bubble in your name and student ID on the scantron. Sign the scantron using your norma
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BCH 3023 Fall 2008 Exam 1, Form A Name: _1. At what pH is the total net charge of lysine equal +1? For lysine, the pKa for the-carboxylate is2.2, the pKa for the -amino group is 8.9, and the pKa for the -aminogroup is 10.5. a. 2.2 b. 5.6 c. 7.5 d. 9.7
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EXIsp09Multiple Choice Identify the choice that best completes the statement or answers the question. 1. A mild reducing agent will most likely affect which of the following amino acids in a protein? a. tryptophan d. cystine b. histidine e. lysine c. ala
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Exam 1 Spring 07 1. What is the molar hydrogen ion concentration of a solution of HCl at pH 2.5? a. 0.00316 b. 0.00250 c. 0.025 d. 0.6021 e. 1.602 2. An acid is designated at "weak" because (BEST ANSWER) a. It requires more base than a strong acid for neu
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1. Which of the following pairs of amino acids would be least resolvable if electrophoresed at ph 7.0? a. lys and flu b. asp and val c. tyr and leu d. phe and gly * net charge on the molecule (will not separate) e. arg and gln 2. which of the following pa
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1. The use of LiAlH, to determine the C-terminus of a protein involves: a. Reduction- CORRECT b. An oxidation c. Denaturation d. A decarboxylation e. Esterification 2. An amino acid contains at least two functional groups: a carboxylic acid and an amine.
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Old Test Reviewed on 2/13/09 Friday 1. Which a.a. does not exist in stereoisomeric form? Glutamine, glutamate, glycine, glutamic acid, cysteine 2. Which tripeptide is most likely found on surface of protein? (the one with most hydrophilic groups) Glu-lys-
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Review for Exam 1 1. The use of LiAl H, to determine the C-terminus of a protein involves: a. Reduction- CORRECT b. An oxidation c. Denaturation d. A decarboxylation e. Esterification 2. An amino acid contains at least two functional groups: a carboxylic
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For EXAM I, BCM 3023 Spring 2005 Under several of these questions, the courses in which you studied background material would have been helpful.l 1. Substances which are optically active: a. rotate plane polarized light b. are fluorescent c. absorb ultrav
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These are some problems to help you practice some of the math related questions on the first exam. Please do not ask questions on how to do the problem if you have not first attempted to do the problem a few times. The TA's will not solve the problems for
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Exam 2 - Spring 07 1. Changes in the configuration around which of the following carbons is responsible for the mutorotation exhibited by glucose in solution? *a. C-1 b. C-2 c. C-4 d. C-5 e. C-6 2. Membranes are likely to be most fluid if they are richest
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BCH 3023 Fall 2008 Exam 2, Form C Name: ANSWER KEY In class, we discussed one method to linearize the Michaelis-Menton equation. There are other methods to do this, one being an Eadie-Hofstee plot. Given the Eadie-Hofstee plot below, answer questions 1 an
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BCH 3023, Fall 2006 Exam 2BCH 3023 Name _ Fall Semester, 2006 Exam 2 ID _ FORM A Bubble in the Test Form Code circle on your scantron with the Form Letter shown above. Bubble in your name and student ID on the scantron. Sign the scantron using your norma
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Exam 2 - Fall 2007 Ch.5, 6, 7,8,10,11 1. Enzymes which act on monosaccharides to change the configuration around a specific carbon atom are called: a. transferases b. reductases c. ligases *d. epimerases e. rotisserases 2. A feature(s) of 2,3 bisphosphogl
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Exam 2 1. Which of the following sequences of duplex DNA will be most resistant to melting? a. ATATCGAA TATAGCTT b. AAATCGAA TTTAGCTT c. CCATTTTG GGTAAAAC d. CCCGGATG GGGCCTAC e. TTCTTGAA AACAACTT 2. The parent compound for the correct naming of the stere
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Exam 2 Spring 07 1. Changes in the configuration around which of the following carbons is responsible for the mutorotation exhibited by glucose in solution? *a. C-1 b. C-2 c. C-4 d. C-5 e. C-6 2. Membranes are likely to be most fluid if they are richest i
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Exam 3 Spring 05 1. Which of the following figures represents the effect of an allosteric inhibitor?1.2e+0 1.2e+01.0e+0A1.0e+0 8.0e-1 6.0e-1 4.0e-1 2.0e-1B6.0e-14.0e-12.0e-1realtive rate8.0e-1realtive rate02040608010012002040608010
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Test 3 Review Questions 1. What is the difference between the lock and key and the induced fit hypothesis for enzyme-substrate binding? 2. What is three-point attachment and why is it important? 3. What is a coenzyme? 4. How can enzyme activity be control
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Exam 3 Spring 04 1. Integral membrane proteins interact extensively with the hydrocarbon chains of membranes lipids. Which amino acid sequence would provide the best interaction? a. Ser Tyr Thr Asn b. Asp Asn Arg Lys c. Lys Gly His Gln d. Phe Arg Ile Val
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Exam 3 Spring 07 1. Which of the following does NOT carry a "high energy" bond? a. PEP b. UDP-glucose c. acetyl CoA d. succinyl CoA *e. pyruvate 2. 32P is a radioactive isotope of phosphorus, often used to trace phosphate or derivatives in metabolic pathw
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ex3sp09 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Which of the following is NOT essential for (or does not accompany) the synthesis of ATP by oxidative phosphorylation? a. membrane potential d. hydro
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BCH 3023, Fall 2006 Exam 3BCH 3023 Fall Semester, 2006 Exam 3 FORM AName _ ID _Bubble in the Test Form Code circle on your scantron with the Form Letter shown above. Bubble in your name and student ID on the scantron. Sign the scantron using your norma
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BCH 3023 Fall 2008 Exam 3, 1/14/2008 Name: _ 1. Identify the following structures: a. Thymine, adenine, cytosine, and guanine b. Cytosine, guanine, thymine, and adenine c. Cytosine, adenine, thymine, and guanine d. Thymine, guanine, cytosine, and adenin
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Test 3 practice problems 1. Given the following reaction calculate the redox potential and the free energy (G '). The Faraday constant is 96,494 JV-1mol-1. NAD+ + FADH2 NADH + H+ + FAD+ NAD+ + H+ + 2e NADH FAD+ + 2H+ + 2e FADH2 Answer: Redox potential = -
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Fluoride inhibits enolase by reaction with Mg+2 to form the precipitate, MgFPO3. What metabolite intermediate will accumulate when F is added to cellfree extracts capable of glycolysis? Describe the reaction mechanisms of aldolase (Schiff base formation,
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ACC 630 Exam 1 Review GuideChapter 12 Intangibles Multiple choice questions are straight from the 6 page chapter summary document's Learning Objectives (L.O.) s 1 through 8 only. Exercise like question(s) relate to homework: E12-11, E12-12* & E12-14 Chap
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CHAPTER 7Cash and ReceivablesLEARNING OBJECTIVES1. Identify items considered cash. 2. Indicate how to report cash and related items. 3. Define receivables and identify the different types of receivables. 4. Explain accounting issues related to recognit
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CHAPTER 16Dilutive Securities and Earnings Per ShareLEARNING OBJECTIVES1. Describe the accounting for the issuance, conversion, and retirement of convertible securities. 2. Explain the accounting for convertible preferred stock. 3. Contrast the account
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CHAPTER17INVESTMENTSIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 17-1Learning Objectives1. 2. 3. 4. 5. 6. 7. 8. I de ntify thethre cate s of de se e gorie bt curitie and de s scribetheaccounting and re porting tre e for
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CHAPTER17INVESTMENTSIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 17-1Lea r ni ng Objecti ves1. 2. 3. 4. 5. 6. 7. 8.Chapter 17-2I denti fy the thr ee categor i es of debt secur i ti es and descr i be the accounti ng and
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CHAPTER23STATEMENT OF CASH FLOWSIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 23-1Learning ObjectivesChapter 23-2S ction 1 - Pre e paration of the FlowsPrimary purpose:S m nt of C tate e ashTo provideinform ation abou
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CHAPTER16DILUTIVE SECURITIES AND EARNINGS PER SHAREIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 16-1Learning Objectives1.De scribetheaccounting for theissuance conve , rsion, and re m nt of conve tire e rtible se curiti
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CHAPTER14LONG-TERM LIABILITIESIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 14-1Learning Objectives1. 2. 3. 4. 5. 6. 7. 8. De scribetheform proce s associate with issuing long-te de al dure d rm bt. I de ntify various typ
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CHAPTER13CURRENT LIABILITIES AND CONTINGENCIESIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 13-1Learning Objectives1. 2. 3. 4. 5. 6. De scribethenature type and valuation of curre liabilitie , , nt s. Explain theclassific
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CHAPTER15STOCKHOLDERS' EQUITYIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 15-1Lea r ni ng Objecti ves1. 2. 3. 4. 5. 6. 7. 8.Di scuss the char acter i sti cs of the cor por ate for m of or gani zati on. I denti fy the ke
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CHAPTER INTANGIBLE12ASSETSIntermediate Accounting 13th Edition Kieso, Weygandt, and WarfieldChapter 12-1Learning Objectives1. 2. 3. 4. 5. 6. 7. 8. 9. 10.De scribethecharacte ristics of intangibleasse ts. Ide ntify thecosts to includein theinitial v