Q&A Hero

Q: 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

Q: Eukaryotic secretory proteins are synthesized and translocated via the endoplasmic reticulum. Order the following sequence of events for this process. A. signal sequence removed. 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

Q: ____ 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

Q: 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. e. all are characteristics.

Q: 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.

Q: The primary function of Met-aminopeptidase is to: a. cleave large inactive pro-proteins. b. remove leader peptides after translocation. c. transfer a Met to the C-terminal end for translocation. d. remove invariable Met and introduce N-terminal diversity. e. all are true.

Q: The most common form of post-translational processing is: a. carbohydrate addition. b. lipid addition. c. phosphorylation. d. adding signal sequences. e. proteolytic cleavage.

Q: Characteristics of Hsp90 chaperones include all EXCEPT: a. 1-2% of total cytosolic proteins in eukaryotes. b. action depends on cyclic binding and hydrolysis of ATP. c. major purpose is conformational regulation of signal transduction molecules. d. directs proteins toward degradation pathways. e. all are true.

Q: Which of the following statements about protein folding is INCORRECT? a. the Hsp70 proteins bind to hydrophilic regions of the protein, thus preventing aggregation b. the Hsp60 proteins are also known as chaperonins c. the GroEL protein provides an environment free from possibility of aggregation d. the GroES protein serves as the cap for GroEL e. all are correct

Q: The folding cycle in the GroES-GroEL complex of E. coliutilizes the following sequence:A. ATP binding to GroELB. GroES dissociates from the complexC. Partially folded protein hydrophobic residues bind GroELD. GroES is recruited to GroELE. GroES promotes ATP hydrolysis and -subunits undergo a conformational change that buries the hydrophobic patchesa. A, B, C, D, Eb. B, A, C, D, Ec. C, D, A, E, Bd. C, A, D, E, Be. D, C, E, A, B

Q: Which of the following statements regarding chaperones and chaperonins is correct? a. GroEL serves as a cap for GroES b. GroES is a large, cylindrical protein complex c. DnaK works with DnaJ to sequester hydrophobic regions of peptides d. while the GroEL-GroES complex requires ATP to aid in protein folding, the DnaK-DnaJ system does not e. all are true.

Q: In E. coli, ____ bound to large ribosomal subunits facilitates transfer to ____ to bind ____ residues, thus avoiding non-productive folding. a. chaperonin; trigger factor; H-binding b. trigger factor; DnaK; hydrophobic c. DnaK; Hsp70; ionic d. Hsp70; chaperonin; hydrophilic e. all are true

Q: In general, proteins whose folding is chaperone-dependent start the folding process first with ____ and then are passed as ____ folded intermediates to ____. a. Hsp40; un-; Hsp70 b. Hsp90; un-; chaperonin c. Hsp70; partially; chaperonin d. Hsp40; partially; Hsp70 e. Hsp60; partially; Hsp40

Q: Which of the following is responsible for Alzheimer's disease? a. polyglutamine aggregates b. neurofibrillary tangles of polymeric microtubule-binding protein tau c. extracellular deposits of amyloid- and intracellular neurofibrillary tangles of microtubule-binding protein tau d. mutation in the huntingtin gene e. none of the above

Q: 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

Q: The primary driving force for folding is/are ____ 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

Q: 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

Q: Which of the following serves as a guanine-nucleotide exchange factor during the elongation cycle? a. EF-Tu b. EF-Ts c. EF-G d. EF-NEF e. none of the above

Q: Which of the following is FALSE regarding peptide chain termination? a. RF-1 recognizes the stop codons UAA and UAG b. RF-3-GTP, along with either RF-1 or RF-2, binds to the P-site of the ribosome c. RRF expels the uncharged tRNA from the P-site d. a glutamine residue in RF-1 and RF-2 positions a water molecule to hydrolyze the peptide from the P-site tRNA e. none of the above

Q: Which of the following correctly describes the order of events in the class I aminoacyl-tRNA synthetase reaction?I. displacement of AMPII. transesterificationIII. nucleophilic attack by 2'-hydroxyl of the tRNA on the acyl adenylateIV. formation of acyl adenylate by reaction of amino acid with ATPV. displacement and subsequent hydrolysis of pyrophosphatea. III, I, IV, V, IIb. III, V, IV, I, IIc. IV, II, I, III, Vd. IV, V, III, I, IIe. IV, I, III, II, V

Q: In a class I aminoacyl-tRNA synthetase, which of the following reacts with the acyl phosphate formed during the reaction of ATP with the amino acid?a. 5'-hydroxyl of the nucleotide on the 5' end of the tRNA moleculeb. 3'-hydroxyl of the nucleotide on the 5' end of the tRNA moleculec. 2'-hydroxyl of the nucleotide on the 5' end of the tRNA moleculed. 3'-hydroxyl of the nucleotide on the 3' end of the tRNA moleculee. 2'-hydroxyl of the nucleotide on the 3' end of the tRNA molecule

Q: Diphtheria toxin is extremely potent and only a few micrograms causes death because it: a. inhibits f-Met-tRNAimet binding. b. is an enzyme and can catalytically modify a number of GTP-dependent enzymes. c. inhibits translocation of peptidyl-tRNA. d. catalyzes inactivation of 28 S tRNA. e. inhibits EF-G:GTP dissociation from ribosomes.

Q: A protein synthesis inhibitor that catalytically inactivates 28S rRNA and is very toxic in eukaryotic cells is: a. ricin. b. puromycin. c. cycloheximide. d. streptomycin. e. tetracycline.

Q: 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

Q: 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.

Q: Each of the following statements regarding ways in which eukaryotic protein synthesis differs from prokaryotic protein synthesis is true EXCEPT: a. prokaryote protein synthesis is initiated by f-Met, while eukaryotic is initiated by Met b. prokaryotes use a 30S small ribosomal subunit, while eukaryotes use a 40S small ribosomal subunit c. prokaryotic and eukaryotic translation initiation differ significantly in mechanism and process d. prokaryotic termination involves three release factors, while eukaryotic termination involves one e. all of the above are true statements

Q: All are characteristics of eukaryotic mRNA EXCEPT: a. poly (A) tail. b. no Shine-Dalgarno sequence. c. codon-binding directs for an initiator tRNA carrying met. d. 5'-7methyl-GTP cap. e. all are characteristics.

Q: 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. 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.

Q: 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

Q: Which of the following proteins is NOT correctly defined? a. IF-2: G-protein that binds to the initial f-met tRNA b. EF-Tu: G-protein that binds aminoacyl-tRNA c. EF-Ts: G-protein that promotes translocation of mRNA d. RF-3: G-protein that is a structural mimic of tRNA e. all are true.

Q: Ribosome:mRNA:P-site tRNA complex, with the help of ____, is disassembled by ____ which is an excellent molecular mimic of a(n) ____. a. ATP; tRNA terminator; GTP b. tRNA; ribosome recycling factor; mRNA c. EF-G; ribosome recycling factor; tRNA d. mRNA; elongation factor; EF-G e. none are true

Q: The termination signal complex transforms the ribosomal peptidyl transferase into a/an: a. lyase. b. isomerase. c. hydrolase. d. transferase. e. ligase.

Q: 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. e. displacement of EF-G by EF-Tu:aminoacyl-tRNA.

Q: "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

Q: 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

Q: Peptidyl transferase catalyzes the reaction in which the nucleophile is: a. oxygen in the carboxylate group of the aminoacyl-tRNA. b. amino nitrogen in the aminoacyl-tRNA. c. amino nitrogen from the peptidyl-tRNA. d. oxygen in the carboxylate group of the peptidyl-tRNA. e. electron pair on a ring N atom of the purine A2451.

Q: The actual peptide bond-forming step in translation is referred to as ____, and is catalyzed by ____. a. peptide bond-formation; peptidase b. transpeptidation; transpeptidase c. peptidyl transfer; peptidyl transferase d. translocation; translocase e. none of the above

Q: Which of the following does not reqire GTP hydrolysis? a. the formation of the initiation complex (translationally active 70 S ribosome complex). b. the binding of the aminoacyl tRNA to the A site during elongation c. translocation with release of the uncharged tRNA during elongation d. the dissociation of release factors from the ribosome. e. all of the above require GTP hydrolysis.

Q: 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. d. binds initiator tRNA and GTP. e. binds to 30 S subunit and drives mRNA binding.

Q: The order of events in the initiation of protein synthesis is: 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-tRNA ifMet 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

Q: 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

Q: 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.

Q: Protein synthesis in bacterial cells usually starts with a: a. methionine residue. b. formylmethionine residue. c. cysteine residue. d. valine residue. e. phenylalanine residue.

Q: Which of the following statements is true regarding the formylmethionine that serves as the first amino acid in bacterial protein synthesis? a. the formyl group is removed during protein synthesis leaving methionine as the first residue in all bacterial proteins b. the tRNA that carries formylmethionine is the same tRNA for methionine c. the formyl group donor is N10-formyl-tetrahydrofolate d. an aminoacyl-tRNA synthetase that is specific for formylmethionine attaches formylmethionine to the tRNA e. none of the above.

Q: 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 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

Q: 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

Q: Mitochondrial and chloroplastic ribosomes resemble ____ ribosomes. a. prokaryotic b. lower eukaryotic c. higher eukaryotic d. no other e. none are true

Q: Peptidyl transferase is the catalytic center of the ribosome and is located: a. on the 30 S subunit near the decoding center. b. on the 30 S subunit near the head. c. on the 50 S subunit near the center protuberance. d. on the 50 S subunit at the bottom of a deep cleft. e. on the 50 S subunit at the cleft of the L7/L12 ridge.

Q: The central domain of the ____S ribosomal subunit serves as the decoding center and is composed only of ____S rRNA. a. 30; 16 b. 30; 5 c. 50; 23 d. 50; 5 e. none are true

Q: The 30S subunit of E. coliribosomes has all the following anatomical characteristics EXCEPT: a. "head". b. "body" or "base". c. "platform". d. "legs". e. all are true.

Q: All are characteristics of ribosomal subunit assembly under appropriate conditions of pH and ionic strength EXCEPT: a. ribosomes self-assemble spontaneously b. no intervention by any additional factors or chaperones is required c. ribosomal proteins bind in a specific order. d. rRNA acts as a scaffold upon which various ribosomal proteins convene e. all are true

Q: Ribosomes constitute about ____ of the dry cell mass of an E. colicell. a. 1% b. 5% c. 10% d. 20% e. 40%

Q: Ribosomal proteins are typically rich in the amino acids ____ and ____ to interact with ____ RNAs. a. asp; glu; polycationic b. asp; ala; polycationic c. lys; ala; polyanionic d. ala; arg; polyanionic e. arg; lys; polyanionic

Q: Which of the following statements is true regarding ribosomes? a. they are found in the cytosol and nucleus of all cells b. prokaryotic ribosomes consist of a 30S and a 50S subunit while eukaryotic ribosomes consist of a 60S and an 80S subunit c. ribosomes consist of both protein and ribonucleic acid with the majority of the mass from the protein component d. since the peptidyl transferase activity is perfomed by RNA, it can be considered a ribozyme e. all are true

Q: ____ are the agents of protein synthesis. a. Nuclei b. Mitochondria c. Chloroplasts d. Ribosomes e. Plasma membranes

Q: ____ converts the language of genetic information embodied in the base sequence of a mRNA molecule into the amino acid sequence of a polypeptide chain. a. Replication b. Translation c. Transcription d. Degradation e. Translocation

Q: Nonsense suppression is the production of isoacceptor tRNAs called ____ tRNAs that read ____ codons and insert an amino acid. a. nonsense; nonsense b. suppressor; nonsense c. suppressor; suppressive d. nonsense; suppressive e. codon; anticodon

Q: All members of a set of tRNAs specific for a particular amino acid - termed ____ tRNA - are served by one ____. a. companion; codon family b. companion; tRNA binding site c. isoacid; tRNA family d. isoacceptor; aminoacyl tRNA synthetase e. none are true

Q: 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.

Q: 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.

Q: 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

Q: 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.

Q: 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. through binding specificity, they relate specific amino acids to appropriate codons. e. they must "read" the anticodon of the tRNA.

Q: Which of the following is/are true regarding the genetic code? a. codons are read 5' to 3' b. there are 20 total "sense" codons, one for each amino acid c. there are three nonsense codons; these are "stop" signals d. a and c are true e. a, b, and c are true

Q: Codons representing the same amino acid or chemically similar amino acids tend to be similar in sequence, often differing only in the third base. This feature is called: a. home-base degeneracy. b. first-base similarity. c. second-base type similarity. d. third-base degeneracy. e. all are true.

Q: 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.

Q: 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.

Q: The linkage between the amino acid and the tRNA in an amino-acyl tRNA complex is: a. an amide b. an acyl phosphate c. a hydroxylamine d. an ether e. an ester

Q: 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.

Q: The adapter molecule that interacts specifically with both nucleic acids and amino acids is: a. rRNA. b. tRNA. c. mRNA. d. ssRNA. e. all are true.

Q: Which of the following is true regarding the araBADoperon? a. binding of arabinose causes dimerization of AraC allowing it to bind to araO2 and araI1 b. when bound to arabinose, the AraC dimer must also bind to a CAP-cAMP dimer for translation to occur c. expression of araC occurs in concert with the expression of araB, araA and araD d. AraC bound to arabinose can bind to CAP regardless of whether or not cAMP is present e. none of the above

Q: The araBAD operon allows for the use of what metabolite by E. coli? a. arachidonic acid b. arabinose c. allose d. altrose e. none of the above

Q: During RNA chain elongation gyrase proceeds ahead of the transcription bubble in order to _____. a. remove negative supercoils by introducing positive supercoils b. remove positive supercoils by introducing negative supercoils c. remove negative supercoils by creating relaxed DNA d. remove positive supercoils by creating relaxed DNA e. none of the above

Q: During RNA chain elongation, ____ follows behind the transcription bubble removing _____ supercoils a. gyrase; negative b. gyrase; positive c. topoisomerase; negative d. topoisomerase; positive e. none of the above

Q: During RNA chain elongation, ____ proceeds ahead of the transcription bubble introducing _____ supercoils a. gyrase; negative b. gyrase; positive c. topoisomerase; negative d. topoisomerase; positive e. none of the above

Q: The production of multiple transcripts from a single gene includes all EXCEPT: a. constitutive splicing. b. use of different promoters. c. selection of different polyadenylation sites. d. alternative splicing of the primary transcript. e. all are true.

Q: Which is/are true of protein isoforms? a. they are related polypeptides b. they have identical structure and function c. they are the result of different transcripts of a single gene d. a and c e. a, b, and c

Q: Spliceosomes include all of the following EXCEPT: a. snRNPs. b. RNA-annealing proteins. c. ATP-dependent RNA-unwinding proteins. d. enzymes catalyzing transesterification of phosphoesters. e. all are components.

Q: Which of the following is required for RNA splicing to occur? a. a free 5 hydroxyl created by hydrolysis of the phosphate ester bond b. a cyclic phospodiester at the 3 end of the RNA molecule c. a 2 hydroxyl group d. the enzyme splicase e. none of the above

Q: The initial event in the conversion of an hnRNA to the mature RNA which leaves the nucleus is: a. formation of ribonucleoprotein particles (RNPs). b. capping the 5'-end of the transcript with a guanylyl group by guanylyl transferase. c. addition of a poly(A) tail to the 3'-end of the transcript by poly(A) polymerase. d. splicing together of the exons. e. transesterification reactions in lariat formation.