Quiz 13 & 14 (L12 CH 15 a&b) PDF

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Dr. Kudus
This is the answer sheet to the multiple choice questions. Many have been repeated each year, and it gives an explanation as to why the correct answer is correct. These can be brought into the test and many test questions may be similar to the MCI's. These have been filled in by st...

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Quiz 13 & 14 (L12 CH 15 a&b) (CONTAINS BOTH QUIZZES) ANSWERS (Mark other answer if there is a discrepancy, please leave a comment for your discrepancy) mRNA structure 1. A Shine-Delgarno sequence (5GGAGG3; also, called the RBS) is present in the bacterial _________ and it is recognized by ________. A. mRNAs/ 23S rRNA B. mRNA/ 16S rRNA C. 16S rRNA/ bacterial mRNA D. 23S rRNA/ bacterial mRNA 2. ______ serve(s) as the start codon of a bacterial mRNA and the anticodon for the start codon is ________? A. 5AUG3/5CAU3 B. 5GUG3/5CAC3 C. 5CUG3/5CAG3 D. 5UUG3/5CAA3 E. Any of these codons/ 5CAU3 3. A polycistronic message of an mRNA gene may have multiple ________. A. RBSs B. start and stop codons C. ORFs D. UTRs E. all these 4. In termination-coupled translation, the translation initiation process is often involved with the sequence_________. A. 5’UAA3’ B. 5’UGG3’ C. 5’AUGA3’ D. 5’AUGU3’ 5. A eukaryotic mRNA may contain all the following except a _________, and the 40S ribosome recognizes the mRNA by _________. A. cap/IRES B. polyA tail/cap C. IRES/polyA tail D. RBS/the cap-binding proteins E. Kozak element (5’G/ANNAUGG3’)/ RBS 6. IRESs are present in some eukaryotic mRNAs and virus mRNAs. An IRES is necessary for _________. A. translation initiation in an internal AUG other than the AUG closest to the cap B. recognition of mRNA by the small subunit ribosome C. translation termination before the normal stop codon D. two of these E. all these

7. In eukaryotic mRNAs, AUG is almost always the start codon, mostly because ________. A. eukaryotes only have one initiator tRNA B. eukaryotes lack a RBS to lock the start codon at the P site C. the pre-initiation complex scans mRNA and stops scanning when the first AUG is reached 8. A reading frame _______, an open reading frame (ORF) ________ of eukaryotic organisms. A. is any nucleotide sequences, taken 3 bases at a time/ usually starts with AUG and ends with UGA, UAA or UGA B. starts with AUG and ends with UGA/ is present in the mRNA but not in the gene C. is present only in the DNA/is present only in the RNA 9. A eukaryotic mRNA has three long ORFs. Which of the ORFs will most likely be translated? A. The one closest to cap site B. The one closest to polyA tail C. The one located in the middle of the mRNA D. It cannot be predicted with any level of precision tRNAs structure 10. What is the cause of stem-loop structure formation found in all tRNAs? A. The presence of internal sequence complementarity in the nucleotide sequences of all tRNAs B. The ability of the modified nucleotides to form nonconventional base-pairing C. The presence of modified nucleotides in all tRNAs D. For all these reasons 11. In theory, every cell should have ______ different anticodon-bearing tRNAs, and there should be ______ tRNAs for arginine. A. 20/1 B. 20/6 C. 61/1 D. 61/6 E. 64/6 12. The amino acid cysteine can be directly attached to the 2’OH or 3’OH end of a tRNA through the _______. A. N of the -NH2 group B. C of the -COOH group C. -O of the -COOH group D. S atom of its side chain (R group) 13. Both bacteria and eukaryotes contain two classes of tRNAs for methionine. Both have the same anticodon but one of them (Met-tRNAi-Met) can directly enter the P site of a ribosome but the other (Met-tRNA-Met) cannot and thus the later one only can read the AUG codons located in the middle of an ORF. Which of the tRNAs is formylated?

A. Met-tRNAi-Met only B. Met-tRNA-Met only C. Both tRNAs 14. If a Met-tRNAi-Met is formylated (i.e. a H-CHO group is attached to the amino acid), its _________ cannot be used in peptide bond formation. A. R group B. -NH2 group C. -COOH group D. -COOH and -NH2 groups 15. There are two groups of tRNAs to carry methionine but methionine has only one codon. Why is an initiator tRNA needed after all? The best answer will be scored. A. Because methionine has a single codon B. So that both the tRNAs for methionine can be utilized C. Because all mature proteins have a methionine at the C-terminus D. Because only the initiator tRNAs can directly enter the P site of a ribosome 16. Which of the following is an aminoacyl tRNA of a bacterium? A. Any tRNA that is carrying a chain of two or more amino acids B. A charged tRNA with a formyl methionine attached to it C. Any charged tRNA other than the initiator tRNA D. A tRNA that just has lost its amino acid AATases 17. A cell has ______ AATases, one for each ______. A. 64/ tRNA B. 61/ tRNA C. 20/ amino acid D. 81/ tRNA and amino acid 18. Before an amino acid can be attached to a tRNA, an AATase must activate an amino acid by attaching a(n) _________ group of an ATP to the O atoms of the COOH group. The amino acid is later transferred to the _______ of a nucleotide of a tRNA. A. pyrophosphate (PO4-PO4)/ nitrogenous base B. phosphate (PO4)/ ribose entity C. ADP/nitrogenous base D. AMP/ribose entity 19. An AATase uses __________ and ___________ as its substrates. A. one amino acid/all the members of an isoaccepting group of tRNAs B. one amino acid/all the tRNAs that contain the anticodon for it C. one tRNA/its legitimate amino acid D. two answer choices are correct E. all answer choices are correct 20. How do aminoacyl tRNA synthetases (AATases) avoid attaching an amino acid to a tRNA with incorrect anticodon? A. An AATase binds a tRNA and recognizes the anticodon loop and the stem of the

acceptor arms of the tRNA B. An AATase binds a tRNA and recognizes the T-Psi-C loop and the D loop of the tRNA C. The AATase reads the anticodon of the tRNA 21. An organism has 19 AATase genes but no AATase for glutmine. How the species charges tRNA with glutamine? A. The species lacks tRNA for glutamine B. The species does not use glutamine for protein synthesis C. The spices charge a tRNA with glutamic acid and then and enzyme converts the glutamic acid of some of the charged tRNAs to glutamine rRNA and ribosomes 22. Which of the following ribosome particles will be the first one to sediment (precipitate down) when centrifuged under standardized conditions? A. 30S B. 40S C. 50S D. 60S E. 70S 23. Which of the following ribosomal subunits would have 3 different molecules of rRNA? A. 30S B. 40S C. 50S D. 60S 24. The 5.8S rRNA is present in the _________ and the 16S rRNA is present in the _________. A. 30S/60S B. 60S/30S C. 50S/40S D. 30S/40S 25. If you could visually examine a ribosome particle, you would mostly see_________. A. rRNA B. tRNA C. proteins D. amino acids 26. RNAs present in the ribosome are mostly_________ molecules. A. linear yet partly ssRNA and partly dsRNA molecules B. circular partly ssRNA and partly dsRNA molecules C. linear ssRNA molecules D. circular ssRNA Peptidyl transferase activity and the decoding center 27. The peptidyl transferase activity is involved in cutting the amino acid (or the polypeptide chain) away from the P site tRNA and attaching the -COOH group of the

amino acid to the -NH2 group of the amino acyl-tRNA present in the A site. Which of the following holds/performs the enzyme activity? A. Small subunit, a protein component B. Small subunit, an rRNA component C. Large subunit, a protein component D. Large subunit, an rRNA component 28. The peptidyl tarnsferase activity is executed by using a/an__________ as the hammer that attacks a carbonyl carbon (C=O) atom of an amino acid; the reaction __________ ATP hydrolysis. A. N atom of an NH2 group of an adenine (nitrogenous base) of the rRNA of the 50S ribosome/ requires B. N atom of the NH2 group of an amino acid of an aminoacyl tRNA/ does not require any C. O of the COOH group of an amino acid of an aminoacyl tRNA/ requires 29. The decoding center is in the ________ subunit ribosome, and it uses the _______ to decode the genetic code. A. large/23 or 28S RNA B. small/ 16 or 18S RNA C. small/ mRNA and tRNA D. large/ peptidyl transferse center 30. The A, P and E sites are ____________. A. present mostly in the 30S or 40S particles B. present mostly in the 50S or 60S particles C. fully formed in the 70S and 80S particles D. present mostly in the 50S or 60S particles, and they are fully formed in the 70S or 80S particles 31. The mRNA enters the 70S or 80S ribosomes through a narrow channel present in the 30S or 40S ribosome so that ___________, and the newly synthesized polypeptide passes through a tunnel present in the 50S or 60S ribosome so that ____________. A. the mRNA does not escape/ the peptide cannot interact with the ribosomal proteins B. the secondary structures of the mRNA are removed/ the peptide chain does not fold except forms alpha helices 32. Ribosomes engaged in protein synthesis in eukaryotic cells are found mostly ___________. A. in the cytoplasm B. in the nucleoplasm C. on the endoplasmic membrane D. inside the cisternae of the endoplasmic reticulum Translation initiation 33. Which of the following is generally the correct order of the translation initiation event in bacteria? A. 30S> fMet-tRNAi> mRNA> 50S> aminoacyl tRNA

B. 30S> mRNA> fMet-tRNAi> 50S> aminoacyl tRNA C. 30S> mRNA > 60S> fMet-tRNAi> aminoacyl tRNA 34. During translation initiation, the eukaryotic 40S ribosomes ___________. A. always bind mRNA before the initiator tRNA B. always bind met-tRNAi before the mRNA C. usually binds met-tRNA and mRNA at the same time D. usually binds 60S ribosome before met-tRNA and mRNA 35. In bacteria, the initiator codon could be 5AUG3, 5GUG3 and 5CUG3, yet the initiator tRNA is charged with methionine alone. The anticodon of the bacterial initiator tRNA is ______? A. 5UAC3 B. 5CAU3 C. 5CAU3, 5CAC3 and 5CAG3 36. Initiation factors (IFs) are required for each of the following purposes but not (except) ____________. A. to prevent the entry of a tRNA to the A site until an initiator tRNA is already in the P site B. to help dissociate small and large subunit ribosomes after translation termination C. to help an initiator aminoacyl tRNA enter the P site D. to help an elongation tRNA enter the P site E. for binding and hydrolyzing GTP 37. There are many initiation factors (eIFs) involved in the eukaryotic translation initiation. Of them, eIF_________ recruit mRNAs in a cap-dependent manner; and the eIF(s)________ prevent the 60S ribosome from prematurely binding the 40S ribosome. A. 2/3 B. 2 and 3/ 4 and 5 C. 4 and 5 / 6 and 7 D. 4A, B, E and G/1, 1A and 5 38. The initiator tRNAs in eukaryotes are recognized and recruited by _________. A. the ribosome itself B. eIF 1 C. eIF 2 D. eIF 4 39. ________ is/are not present in a eukaryotic 48S pre-initiation complex. A. eIF1, 1A, 2, 3, and 5 B. eIF4A, B, E and G C. 60S ribosome D. mRNA 40. The enzyme that acts as helicase to straighten the secondary structures of the 5’UTR of the mRNA and transports the pre-initiation complex to the first AUG is eIF4_______, and the codon 5AUG3 is actually identified by ________.

A. A/ the initiator tRNA B. G/eIF5B C. E/eIF5 D. B/eIF3 Translation Elongation, peptidyl transrase reaction, and mRNA translocation 41. An aminoacyl tRNA enters the A site of a bacterial ribosome _______. A. only after the last of the initiation factors has left the pre-initiation complex B. if EF TU-GTP helps the aminoacyl tRNA molecule to enter the A site C. after the 70S ribosome has been assembled D. if two of these conditions are met E. if all these conditions are met 42. Suppose the codon of the mRNA in the A site is 5CCC3 but the anticodon of the aminoacyl tRNA is 5GGA3. The ribosome may prevent the incorrect tRNA from taking part in protein synthesis by each of the following processes except________? A. The wrong tRNA blocks the A site and prevent elongation, leading to the disassembly of the 70S ribosome B. A 70-degree accommodation of the tRNA relative to the initiator tRNA would eliminate the wrong tRNA C. The 16S RNA of the decoding center would not stabilize the inaccurate anticodoncodon hybridization D. The EF TU-GTP would leave the ribosome if the codon-anticodon hybridization is inaccurate 43. The codon is 5CAA3. Which of the following tRNAs would certainly survive the accommodation challenge imposed on the tRNA by the ribosome? A. One with anticodon 5UUG3 B. One with anticodon 5CAA3 C. One with anticodon 5AAC3 D. One with anticodon 5TTG3 44. The peptydyl transferase activity removes the amino acid (or the polypeptide chain) from the ________ tRNA and attaches the amino acid (or the peptide chain) to the ____________. A. A site tRNA/ 3OH end of the P site tRNA B. P site tRNA/ 3OH end of the A site tRNA C. P site tRNA/ the amino acid of the A site tRNA D. A site tRNA/ the amino acid of the P site tRNA 45. After peptidyl tranferase reaction is completed, the A site tRNA always becomes a/an _______tRNA, and the P site tRNA always becomes a/an ________ tRNA. A. uncharged/ peptidyl B. peptidyl/uncharged C. peptidyl/aminoacyl D. uncharged/aminoacyl 46. Translocation is moving the mRNA from the 3’ to the 5’ direction of the mRNA by exactly one codon (three nucleotides). This is done by EFG (for bacteria) or eEF2

(for eukaryotes) using GTP hydrolysis. The translocation process involves (roughly) __________. A. pushing the tRNA (while it is attached to the mRNA) across the small subunit ribosome B. pulling the mRNA across the small subunit ribosome C. pushing the small subunit ribosome D. pulling the small subunit ribosome 47. EFG -GDP complex is structurally a tRNA mimic. It means ___________. A. EEFG-GDP interacts with ribosome like a tRNA B. EFG-GDP is structurally similar to a tRNA C. EFG is made of tRNA D. two of the options E. all these options 48. A tRNA was charged with a wrong amino acid. Who made the mistake, and will the wrongly charged tRNA enter in the A site of the ribosome and its amino acid used in protein synthesis? A. small subunit ribosome/no B. large subunit ribosome/ yes C. aminoacyl tRNA synthetase/ no D. aminoacyl tRNA synthetase/ yes 49. Suppose you mutated the anticodon AUG (for Methionine) of a tRNA gene to AUC (for isoleucine) but left the other nucleotides of the tRNA intact. Will this mutant tRNA be charged with methionine? A. Most likely no B. Most likely yes C. Cannot be predicted at all Translation termination 50. There are two classes of release factors in bacteria, of them class I release factors ________ and the class II release factors _______. A. recognize the stop codons/ disassociate the 70S (or 80S) ribosomes B. recognize the stop codons/ push out the class I release factors from the P site C. recognize the stop codons/ cut away the polypeptide chain from the P site tRNA D. push out the class I release factors from the P site/ disassociate the 70S (or 80S) ribosomes 51. The class I release factors must have ________. A. the enzyme activity that cuts the O-C bond between the tRNA and the polypeptide chain B. ability to push the 40S ribosome away from the 60S ribosome C. ability to interact with the stop codons of the mRNA D. two of these abilities E. all these abilities 52. The eukaryotic class I release factor eERF recognizes the stop codon(s)___________.

A. UAA B. UAG C. UGA D. UAA and UAG E. UAA, UAG and UGA 53. Which of the bacterial release factors remove(s) the polypeptide chain from the peptidyl tRNAs? A. RF1 B. RF2 C. RF3-GTP D. RF1 and RF2 E. RF2 and RF3-GTP Translation regulation 54. Which of the following is the minimal but most efficient method of global suppression of translation? A. Destroying the rRNA of the 30S or 40S ribosomes B. Destroying the proteins of the 50S or 60S ribosomes C. Chemically modifying one or more key IFs, EFs of RFs D. completely depleting one or more amino acids from the cell 55. The phosphorylation of the 4E binding protein (i.e. 4E-BP) activates translation because the modified 4E-BP_______. A. cannot bind eIF4E B. binds eIF4E more efficiently C. cannot phosphorylate eIF4E 56. The iron regulatory element (IRE) of the ferritin mRNA is a _________. A. riboswitch B. transcription factor C. RNA sequence recognized by ferritin D. RNA secondary structure recognized by ferritin E. RNA secondary structure recognized by the iron regulatory protein (IRP) 57. The iron regulatory protein (IRP) found plenty of iron (Fe++) in the cell and bound the iron ions. IRP-Fe++ complex would ________ ferritin mRNA. A. not be able to bind IRE, it will allow translation of the B. bind IRE and activate the translation of the C. act as a nuclease and destroy the 58. A mRNA has a nonsense mutation (a mutation that converts a codon to a stop codon) in the middle of the second exon. The mRNA has five exons. What will happen to this mRNA and its translation? A. The mRNA will be translated but the translation will not be terminated B. The mRNA will be destroyed by the nucleases C. The mRNA will not be translated 59. If an mRNA is broken or its stop codon is mutated to a codon, it causes a serious

problem. The problem is in ______. A. ribosome recycling B. translation initiation C. translation elongation D. translation initiation and elongation E. translation termination and ribosome recycling 60. The tmRNA rescues ribosomes stalled on an mRNA lacking a stop codon. The protein generated from the broken/mutated mRNA becomes tagged and is destined for proteolytic destruction. The tag is ________ . A. the tmRNA attached to the protein B. a series of amino acids at the N-terminal end of the protein C. a series of amino acids at the C-terminal end of the protein 61. The ribosomal proteins of E. coli are encoded in several operons. When there is no rRNA in the cell, the cell does not need any ribosomal proteins. In this situation, one of ribosomal proteins acts as a translational regulator (it inhibits the translation of the mRNA). How the protein does this? A. It binds 30S ribosome and stop it from initiating B. It binds the secondary structures of rRNA C. It binds the RBS of its own mRNA 62. Chloramphenicol, a highly effective antibiotic used in treating bacterial infection, binds the peptidyl transferase center of the _______ ribosome particle(s). A. 30S B. 50S C. 40S D. 60S E. 50S and 60S 63. A bacterium became erythromycin-resistant because of a genetic mutation. Which of the following genes of the bacterium has mutated? A. 16S rRNA gene B. 26S rRNA gene C. One or more tRNA genes D. IF and/or EF and/or RF genes 64. Diphtheria toxin kills human cells by modifying the eEF2, thereby inhibiting translation _________. A. initiation B. elongation C. termination D. initiation and elongation E. elongation and termination...