Deck 30: Protein Synthesis

Question 1

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

Answer 1

D

Question 2

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

Answer 2

E

Question 3

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

Answer 3

E

Question 4

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.

Question 5

____ are the agents of protein synthesis.

A) Nuclei
B) Mitochondria
C) Chloroplasts
D) Ribosomes
E) Plasma membranes

Question 6

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

Question 7

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.

Question 8

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.

Question 9

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

Question 10

Ribosomes constitute about ____ of the dry cell mass of an E. coli cell.

A) 1%
B) 5%
C) 10%
D) 20%
E) 40%

Question 11

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.

Question 12

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

Question 13

All of the statements about the tRNA molecule with the anticodon 5'CAU are correct EXCEPT:

A) It is the anticodon for tRNA_fmet.
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.

Question 14

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.

Question 15

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

Question 16

____ 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

Question 17

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.

Question 18

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.

Question 19

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.

Question 20

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

Question 21

Mitochondrial and chloroplastic ribosomes resemble ____ ribosomes.

A) prokaryotic
B) lower eukaryotic
C) higher eukaryotic
D) no other
E) none are true

Question 22

Protein synthesis in bacterial cells usually starts with a:

A) methionine residue.
B) formylmethionine residue.
C) cysteine residue.
D) valine residue.
E) phenylalanine residue.

Question 23

The termination signal complex transforms the ribosomal peptidyl transferase into a/an:

A) lyase.
B) isomerase.
C) hydrolase.
D) transferase.
E) ligase.

Question 24

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.

Question 25

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

Question 26

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 _i^fMet 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

Question 27

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.

Question 28

"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

Question 29

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.

Question 30

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

Question 31

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

Question 32

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.

Question 33

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

Question 34

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

Question 35

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-tRNA_i^fMet.
E) all are true.

Question 36

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

Question 37

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.

Question 38

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.

Question 39

The 30S subunit of E. coli ribosomes has all the following anatomical characteristics EXCEPT:

A) "head".
B) "body" or "base".
C) "platform".
D) "legs".
E) all are true.

Question 40

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

Question 41

Discuss the triplet codons that represent the same amino acid or chemically similar amino acids.​

Question 42

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 molecule
B) 3′-hydroxyl of the nucleotide on the 5′ end of the tRNA molecule
C) 2′-hydroxyl of the nucleotide on the 5′ end of the tRNA molecule
D) 3′-hydroxyl of the nucleotide on the 3′ end of the tRNA molecule
E) 2′-hydroxyl of the nucleotide on the 3′ end of the tRNA molecule

Question 43

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

Question 44

Discuss the steps involved in peptide chain elongation.​

Question 45

Explain the Wobble hypothesis.​

Question 46

Discuss the two distinct classes of aminoacyl-tRNA synthetases.​

Question 47

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.

Question 48

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

Question 49

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

Question 50

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.

Question 51

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

Question 52

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.

Question 53

Discuss the structure of prokaryotic ribosomes.​

Question 54

Which of the following correctly describes the order of events in the class I aminoacyl-tRNA synthetase reaction?
I) displacement of AMP
II) transesterification
III) nucleophilic attack by 2′-hydroxyl of the tRNA on the acyl adenylate
IV) formation of acyl adenylate by reaction of amino acid with ATP
V) displacement and subsequent hydrolysis of pyrophosphate

A) III, I, IV, V, II
B) III, V, IV, I, II
C) IV, II, I, III, V
D) IV, V, III, I, II
E) IV, I, III, II, V

Question 55

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.

Question 56

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

Question 57

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.

Question 58

Diphtheria toxin is extremely potent and only a few micrograms causes death because it:

A) inhibits f-Met-tRNA_i^met 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.