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A卷 1. 2. Operons are a(n) ____________ sequence lying adjacent to the DNA being transcribed and are composed of a promoter located next to a(n) _______ that interacts and is controlled by a(n) _______ protein. A. initiation; operator; repression B. operator; repressor; regulatory C. regulatory; repressor; activator D. regulatory; operator; regulatory E. none are true In prokaryotes, gene expression is often responsive to small molecules where increasing synthesis of enzymes for metabolism of a certain substrate is termed ___________ and the substrate is called ___________. Likewise metabolic products that decrease synthesis of enzymes for their production are called ________ and carry out ____________. A. autoregulation; regulatory; co-repressors; initiation B. co-induction; induction; co-repressors; initiation 3. 4. 5. 6. 7. C. induction; co-inducer; co-repressors; repression D. induction; co-inducer; repressor; co-repression E. all are true Expression of genes independently of regulation is termed: A. negative regulation. B. constitutive expression. C. transcription expression. D. repressible regulation. E. autoregulation. All are components of the lac operon EXCEPT: A. the structural genes for lacZ, lacY and lacA. B. the operator and promoter sequences. C. lacI gene. D. promoter for the lacI gene. E. all are correct. All are lac repressor properties EXCEPT: A. tetrameric protein expressed constitutively. B. binding site for DNA. C. binding site for mRNA. D. binding site for inducer. E. blocks elongation so initiation is aborted. Repressible operons are expressed only in the _________ of their co-repressor and inducible operons are transcribed only in the _____ of _______ co-inducers. A. absence; presence; small molecule B. presence; presence; small molecule C. presence; absence; protein D. absence; presence; protein E. absence; absence; cAMP receptor protein When the cellular level of tryptophan decreases in E. coli: A. tryptophan-bound Trp repressor associates with trp operator. B. Trp aporepressor has lowered affinity for trp promoter allowing RNA. 8. polymerase binding and transcription of the trp operon. C. tryptophan binds trp inducer to promote positive control of trp promoter. D. trp repressor has a greater affinity for trp operator. E. none of the above. All are characteristics of control mechanisms that regulate transcription in prokaryotes EXCEPT: A.protein : protein interactions are an essential component of transcription regulation. B. DNA : protein interactions are central to transcription regulation. C. regulatory proteins commonly bind DNA at sites of at least partial dyad symmetry or inverted repeats. D. regulatory proteins receive cues that signal the status of the environment of the cell. 9. 10. 11. 12. E. all are characteristics. The recurring structural feature in DNA-binding proteins is the presence of ____________ segments that fit into the _______ grove of B-DNA. -helix; major -sheet; major C. -turn; minor D-barrel; minor E. all are true The base-pair edges in the ______ groove act as a(n) ____________ identifiable through __________ with specific proteins. A. minor; enhancer; H-bonding B. minor; recognition matrix; H-bonding C. major; recognition matrix; H-bonding D. major; repressor; ionic binding E. major; transcriptional silencer; ionic bonding Lac repressor is an example of the DNA-binding motif common to many prokaryotic regulatory proteins and is: A. a homeobox. B. a zinc finger. C. a basic region-leucine finger. D. a helix-turn-helix. E. none of the above. Amino-acyl-tRNA synthetases catalyze the reaction of a: A. specific amino acid attachment to the 3'-OH at the 3'-CCA of a specific tRNA. B. specific amino acid attachment to the 5'-OH at the 5'-CCA of a specific tRNA. C. specific tRNA with ATP to form a so called "charged tRNA" that interacts with a specific site on mRNA. D. all of the above. E. none of the above. 13. 14. 15. 16. 17. 18. The genetic code has all of the following characteristics EXCEPT: A. It is degenerate. B. It is read 3' to 5'. C. It is read from a fixed starting point without punctuation. D. It is not overlapping. E. A group of three bases codes for one amino acid. The genetic code is said to be degenerate, which means that: A. Each codon codes for more than one amino acid. B. An anticodon can interact with more than one codon in the mRNA in which the codon may differ in any or all of the three nucleotides. C. Most amino acids are coded for by more than one codon. D. The code is universally used by virtually all species. E. None are true. Aminoacyl-tRNA synthetases exhibit all of these characteristics EXCEPT: A. some are monomeric and others are oligomeric. B. they attach the amino acid to the 2'- or the 3'-hydroxyl of the ribose located at the 5'-end of the tRNA. C. they attach the amino acid to a terminal adenylate residue on the tRNA. D. they bridge the information gap between amino acids and codons. E. they must "read" the anticodon of the tRNA. An important difference between a class I and class II aminoacyl-tRNA synthetase is: A. The two classes proceed through different aminoacyl-AMP intermediates. B. Class I synthetases first attach the amino acid to the 2'-hydroxyl on ribose, whereas class II attach them to the 3'-hydroxyl. C. Class I synthetases attach amino acids to the 5'-end of the tRNA, whereas class II attach them to the 3'-end. D. The 5'-end of the tRNA molecule is phosphorylated only for those tRNAs recognized by class I synthetases. E. None are true. The anticodon of a tRNA is 5'UUG. What codon(s) can be theoretically recognized by this tRNA? A. 5'CAA only B. 5'CAA & 5'CAG C. 5'AAC only D. 5'AAC & 5' GAC E. 5'CAC only All of the statements about the tRNA molecule with the anticodon 5'CAU are correct EXCEPT: A. It is the anticodon for tRNAfmet. B. The wobble base in the anticodon would be cytosine. C. Its anticodon can theoretically base pair with up to three different codons. D. Its anticodon can base pair to the codon 5'AUG. E. All are correct. 19. 20. All are true for the "wobble position" EXCEPT: A. It is the third base of the codon. B. A certain amount of play might occur in base pairing at this position. C. The first-base anticodon U could recognize either an A or G in the wobble position. D. The first-base anticodon G could recognize either a U or C in the wobble position. E. All are true. Mitochondrial and chloroplastic ribosomes resemble ________ ribosomes. A. prokaryotic B. lower eukaryotic C. higher eukaryotic D. no other E. none are true 21. Protein biosynthesis in all cells utilizes energy driving the assembly process provided by ______ hydrolysis. A. ATP B. GTP C. UTP D. CTP E. None of the above 22. The appropriate order for the basic steps of protein synthesis are: A. The elongation reaction transfers the peptide chain from the peptidyl-tRNA in the P site to the aminoacyl-tRNA in the A site. B. The P site is occupied by peptidyl-tRNA carrying the growing polypeptide chain. C. Binding of mRNA by the small subunit followed by association of a particular initiator aminoacyl-tRNA that recognizes the first codon. D. The large ribosomal subunit joins the initiation complex, preparing it for the 23. 24. elongation stage. E. The new, longer peptidyl-tRNA moves from the A site into the P site as the ribosome moves one codon further along the mRNA. A. A, C, E, B, D B. B, E, C, D, A C. C, D, A, B, E D. D, C, E, B, A E. C, D, B, A, E All are components required for peptide chain initiation EXCEPT: A. mRNA. B. 30S and 50S ribosomal subunits. C. initiation factors. D. GTP and f-Met-tRNAifMet. E. all are true. The Shine-Dalgarno sequence found in prokaryotic systems resides on the ___ end of _____ and is the ________ site. A. 3’; peptidyl-tRNA; formyl transferase B. 5’; DNA; polymerase binding C. 3’; rRNA; initiation factor binding D. 5’; mRNA; ribosome binding E. 3’; aminoacyl-tRNA; formyl methionine binding 25. The order of events in the initiation of protein synthesis is: 26. A. GTP hydrolysis triggered by the 50 S subunit joining the 30 S subunit releasing IF-1, IF-2 and IF-3. B. IF-2 delivers the initiator f-Met-tRNAifMet in a GTP-dependent process. C. A-site of the 70 S initiation complex is ready to accept an incoming aminoacyl-tRNA. D. IF-3 and IF-1 bind 30 S subunit. E. mRNA binds to form the 30 S initiation complex. A. C, A, E, B, D B. E, D, A, B, C C. B, D, C, E, A D. D, B, E, A, C E. D, E, A, B, C Elongation factor Tu (EF-Tu): A. binds GTP promoting translocation of ribosomes along mRNA. B. displaces GDP from the elongation complex. C. binds aminoacyl-tRNA in the presence of GTP. 27. 28. 29. 30. D. binds initiator tRNA and GTP. E. binds to 30 S subunit and drives mRNA binding. GTP hydrolysis is essential for all of the following EXCEPT: A. the formation of the initiation complex (translationally active 70 S ribosome complex). B. the elongation step of translation. C. the translocation step of translation. D. the binding of release factors to the ribosome. E. all utilize GTP hydrolysis. The energy expenditure for protein synthesis is at least ____ high-energy phosphoric anhydride bonds per amino acid. A. 0 B. 1 C. 2 D. 3 E. 4 “Stop” or nonsense codons are recognized by __________ through specific __________ sequences that serve an equivalent of the ________ loop. A. tRNA; nucleotide; anticodon B. nucleotides; complementary; anticodon C. release factors; nucleotide; codon D. release factors; tripeptide; tRNA anticodon E. tRNA; tripeptide; tRNA anticodon Termination of translation in prokaryotic cells requires: A. binding of the terminator tRNA to the termination codon. B. interaction of release factors with the termination codon. C. ternary interaction of the release factor and the termination tRNA with the termination codon. D. release factor interaction with the Shine-Dalgarno sequence and subsequent dissociation of the two ribosomal subunits. 31. 32. 33. E. displacement of EF-G by EF-Tu:aminoacyl-tRNA. All are GTP binding proteins EXCEPT: A. IF-2. B. EF-Tu. C. EF-G. D. RF-3. E. all are true. Intact 70S ribosomes are _______ in initiation of protein synthesis because ______ 30S subunits can interact with initiation factors. A. active; bound B. inactive; only free C. active; open D. inactive; mRNA bound E. all are true IF-3 is important in the initiation of translation in prokaryotic cells in all EXCEPT: A. It binds to the 30 S subunit and is required for the binding of the mRNA to this subunit. B. Its association with the 30 S subunit prevents association with the 50 S subunit. 34. 35. 36. 37. C. Its dissociation from the 30 S subunit permits formation of the initiation complex for translation. D. It binds the 70 S subunit to promote binding of a new mRNA. E. All are important. A dominant mechanism for control of eukaryotic peptide chain initiation is: A. allosteric regulation. B. cofactor availability control. C. competitive inhibition. D. phosphorylation/dephosphorylation. E. ribosylation. Which inhibitor of protein synthesis competes with aminoacyl-tRNAs for binding to the A-site of the ribosome? A. puromycin B. erythromycin C. streptomycin D. cycloheximide E. tetracycline The information for folding each protein into its unique three-dimensional architecture resides within its ________________. A. primary structure B. amino acid content C. content of hydrophobic amino acids D. content of basic amino acids E. none are true The primary driving force for folding is _________ and if crowding occurs then ______________ is likely. A. hydrogen bonding; dehydration B. hydrogen bonding; non-specific bonding C. hydrophobic interactions; aggregation D. hydrophilic interactions; non-specific binding E. none are true 38. 39. 40. Nascent (newly formed) proteins are often assisted in folding and ____________ by a family of helper proteins known as ______________. A. unfolding; molecular principals B. refolding; molecular principals C. refolding; molecular chaperones D. unfolding; molecular chaperones E. unfolding; amyloids All are characteristics of chaperonins EXCEPT: A. allow folding to proceed in a protected environment. B. large, cylindrical protein complexes. C. sequester partially folded proteins. D. formed of two stacked rings of subunits. E. all are true. The folding cycle in the GroES-GroEL complex of E. coli utilizes the following sequence: A. ATP binding to GroEL B. GroES dissociates from the complex C. Partially folded protein hydrophobic residues bind GroEL D. GroES is recruited to GroEL E. GroES promotes ATP hydrolysis and -subunits undergo a conformational change that buries the hydrophobic patches A. A, B, C, D, E B. B, A, C, D, E C. C, D, A, E, B D. C, A, D, E, B E. D, C, E, A, B 41. 42. Proteolytic cleavage has been shown to be involved in all of the following processes EXCEPT: A. inactivation of regulatory enzymes. B. elimination of the N-terminal Met residue. C. activation of zymogens. D. elimination of signal sequences after the protein has reached its proper location. E. digestion of dietary proteins. Characteristics of protein translocation systems include all EXCEPT: A. proteins to be translocated are made as pre-proteins containing contiguous blocks of amino acid sequences that act as sorting signals. B. membranes involved in translocation have specific protein receptors exposed on their cytosolic faces. C. translocons catalyze movement of the proteins across the membrane and metabolic energy in the form of ATP, GTP, or membrane potential is essential. D. pre-proteins are maintained in a loosely folded, translocation-competent conformation through interaction with molecular chaperones. 43. 44. E. all are characteristics. ______recognize the sorting signals as they emerge from the ribosome and together with _____deliver the nascent protein chain to specific membrane complexes called ____ that mediate integration into and across the membrane. A. Signal recognition particles; signal receptors; translocons B. Signal receptors; translocons; signal recognition particles C. Translocons; signal recognition particles; signal receptors D. Signal receptors; signal recognition particles; translocons E. Translocons; signal receptors; signal recognition particles Eukaryotic secretory proteins are synthesized and translocated via the endoplasmic reticulum. Order the following sequence of events for this process. A. signal sequence removed. 45. 46. 47. 48. B. glycosylation in the ER lumen. C. signal sequence synthesis on ribosomes. D. SRP binds signal sequence and subsequently binds SRP-receptor. E. ribosome dissociates. A. A, C, E, B, D B. C, D, A, B, E C. C, A, D, B, E D. A, C, B, D, E E. C, B, D, E, A The ribosome and the _______ form a common conduit for transfer of the nascent protein through the ____________ membrane. A. translocon; endoplasmic reticulum B. signal sequence; plasma C. EF-G; endoplasmic reticulum D. chaperonin; plasma E. all are true Proteins with _____________ sequences remain embedded in the ER membrane with their ____-termini on the cytosolic face of the ER. A. translocator; N B. leader; C C. translocational; N D. stop-transfer; C E. translocon; N The proper sequence for transport of inner mitochondrial membrane proteins would be: A. TOM; SAM. B. TOM; TIM23. C. SAM; TOM; TIM22. D. TOM; TIM22. E. SAM; TOM; TIM22. Protein degradation is compartmentalized either in macromolecular structures known as ______________ or in degradative organelles such as ___________. A. ribosomes; endoplasmic reticulum B. ribosomes; Golgi C. proteosomes; mitochondria D. proteosomes; lysosomes E. lysosomes; endoplasmic reticulum 49. The appropriate sequence for ubiquitination of proteins to be degraded is: A. multiple ubiquitinations may occur on a protein substrate, B. ubiquitin-protein ligase (E3) transfers ubiquitin to free amino groups on the protein, C. E3 selects a protein for degradation by the nature of the N-terminal amino acid, D. ubiquitin-carrier protein (E2) picks up ubiquitin, E. ubiquitin-activating enzyme (E1) attaches via ATP-dependent formation of thioester bond to C-termini of ubiquitin, A. A, C, B, D, E B. E, D, A, B, C C. D, E, C, A, B D. C, E, D, B, A E. E, D, C, B, A 50. In the proteosomes, the 19S cap acts as a ___________ complex for the recognition and selection of _________ proteins for ________ by the 20S proteosomes core. A. B. C. D. E. hydrolysis; unfolded; disposal regulatory; unfolded; disposal hydrolysis; ubiquitinylated; degradation regulatory; ubiquitinylated; degradation all are true