Deck 30: Protein Synthesis

Question 1

Which of the following is NOT a characteristic exhibited by aminoacyl-tRNA synthetases?

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.

Answer 1

B

Question 2

What is the linkage between the amino acid and the tRNA in an amino-acyl tRNA complex?

A)an aminoacyl ester
B)an amide
C)an acid anhydride
D)a diester

Answer 2

A

Question 3

Which of the following is an important difference between a class I and a class II aminoacyl-tRNA synthetase?

A)The 2 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.

Answer 3

B

Question 4

Which of these reactions do amino-acyl-tRNA synthetases catalyze?

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)specific tRNA with GTP to form a so-called "charged tRNA" that interacts with a specific site on mRNA

Question 5

Which of the following is NOT a characteristic of the "wobble position"?

A)It is the first 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.

Question 6

Which of the following is a feature of isoacceptor tRNAs called suppressors?

A)They read suppressive codons and insert an amino acid.
B)They read nonsense codons and insert an amino acid.
C)They read anticodon codons and insert an amino acid.
D)They read mutated codons and insert an amino acid.

Question 7

What is the adapter molecule that interacts specifically with both nucleic acids and amino acids?

A)rRNA
B)tRNA
C)mRNA
D)ssRNA

Question 8

Codons representing the same amino acid or chemically similar amino acids tend to be similar in sequence,often differing only in the third base.What is this feature called?

A)home-base degeneracy
B)first-base similarity
C)second-base type similarity
D)third-base degeneracy

Question 9

Which amino acids are rich in ribosomal proteins and serve to interact with polyanionic RNAs?

A)Arg and Lys
B)Asp and Ala
C)Lys and Ala
D)Ala and Arg

Question 10

Which of the following is NOT a characteristic of the genetic code?

A)Each single amino acid is represented by several codons.
B)Codons are read 5' to 3'.
C)There are 20 total "sense" codons,1 for each amino acid.
D)There are 3 nonsense codons;these are "stop" signals.

Question 11

Which of the following is NOT a characteristic of ribosomal subunit assembly under appropriate conditions of pH and ionic strength?

A)Ribosomes assembly is energy dependent and not spontaneous.
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.

Question 12

Which of these cellular components are the agents of protein synthesis?

A)nuclei
B)mitochondria
C)chloroplasts
D)ribosomes

Question 13

Which of the following is NOT a characteristic of the genetic code?

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.

Question 14

Which of the following is NOT a feature of the tRNA molecule with the anticodon 5'CAU?

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 3 different codons.
D)Its anticodon can base pair to the codon 5'AUG.

Question 15

What is the term for all members of a set of tRNAs specific for a particular amino acid?

A)companion
B)tRNA family
C)isoacid
D)isoacceptor

Question 16

The genetic code is said to be degenerate.What does this imply?

A)Each codon codes for more than 1 amino acid.
B)An anticodon can interact with more than 1 codon in the mRNA in which the codon may differ in any or all of the 3 nucleotides.
C)Most amino acids are coded for by more than 1 codon.
D)The code is universally used by virtually all species.

Question 17

The anticodon of a tRNA is 5'UUG.What codon(s)can be recognized,theoretically,by this tRNA?

A)5'CAA only
B)5'CAA & 5'CAG
C)5'AAC only
D)5'AAC & 5' GAC

Question 18

Which of the following is NOT a characteristic of ribosomes?

A)They are found in the endoplasmic reticulum of all cells.
B)Prokaryotic ribosomes consist of a 30S and a 50S subunit.
C)Ribosomes consist of both protein and ribonucleic acid.
D)The catalytic centre of the large subunit is a peptidyl transferase.

Question 19

Approximately how much of the dry cell mass of an E.coli cell consists of ribosomes?

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

Question 20

Which of these actions 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)translocation
B)translation
C)transcription
D)degradation

Question 21

Which nucleophile is employed by the peptidyl transferase-catalyzed reaction?

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

Question 22

Peptidyl transferase is the catalytic centre of the ribosome.Where is it located?

A)on the 30 S subunit near the decoding centre
B)on the 30 S subunit near the head
C)on the 50 S subunit near the centre protuberance
D)on the 50 S subunit at the bottom of a deep cleft

Question 23

Which of these steps is required for termination of translation in prokaryotic cells?

A)displacement of EF-G by EF-Tu:aminoacyl-tRNA
B)ternary interaction of the release factor and the termination tRNA with the termination codon
C)interaction of release factors with the termination codon
D)release factor interaction with the Shine-Dalgarno sequence and subsequent dissociation of the 2 ribosomal subunits

Question 24

What is the minimum number of high-energy phosphoric anhydride bonds per amino acid required as energy expenditure for protein synthesis?

A)0
B)2
C)4
D)6

Question 25

Which nucleotide and its hydrolysis provide the driving energy for protein biosynthesis in all cells?

A)ATP
B)GTP
C)UTP
D)CTP

Question 26

Which of the following recognizes "stop" or nonsense codons through specific tripeptide sequences that serve as an equivalent of the tRNA anticodon loop?

A)tRNA
B)nucleotides
C)rRNA
D)release factors

Question 27

Which of the following is NOT a component required for peptide chain initiation?

A)DNA
B)30S and 50S ribosomal subunits
C)initiation factors
D)GTP and f-Met-tRNAi^fMet

Question 28

By what factor is protein synthesis faster in prokaryotic cells than in eukaryotic cells?

A)2
B)10
C)30
D)40

Question 29

The actual peptide bond-forming step in translation is referred to as peptidyl transfer.Which enzyme catalyzes this process?

A)peptidase
B)transpeptidase
C)peptidyl transferase
D)translocase

Question 30

What is the function of elongation factor Tu (EF-Tu)?

A)to bind GTP promoting translocation of ribosomes along mRNA
B)to bind to 30S subunit and drive mRNA binding
C)to bind aminoacyl-tRNA in the presence of GTP
D)to bind initiator tRNA and GTP

Question 31

Which of the following processes does NOT require GTP hydrolysis?

A)the formation of the initiation complex (translationally active,70S ribosome complex)
B)the elongation step of translation
C)the translocation step of translation
D)the binding of release factors to the ribosome

Question 32

The ribosome:mRNA:P-site tRNA complex,with the help of EF-G,is disassembled by ribosome recycling factor.Which of the following is the ribosome recycling factor an excellent molecular mimic of?

A)GTP
B)mRNA
C)tRNA
D)EF-G

Question 33

What type of ribosomes do mitochondrial and chloroplastic ribosomes resemble?

A)prokaryotic
B)lower eukaryotic
C)higher eukaryotic
D)viral

Question 34

Which of the following is NOT involved in the initiation of protein synthesis?

A)GTP hydrolysis is triggered by the 50S subunit joining the 30S 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 70S initiation complex is ready to accept an incoming aminoacyl-tRNA.
D)IF-2 and IF-3 bind the 30S subunit.

Question 35

Which amino acid residue is used at the beginning of protein synthesis in bacterial cells?

A)methionine
B)formylmethionine
C)cysteine
D)phosphoserine

Question 36

The Shine-Dalgarno sequence found in prokaryotic systems resides on the 5'-end of mRNA.What function does the site serve?

A)It is for formylmethionine binding.
B)It is for polymerase binding.
C)It is for initiation factor binding.
D)It is for ribosome binding.

Question 37

Which of the following is NOT a basic step in protein synthesis?

A)The elongation reaction transfers the peptide chain from the peptidyl-tRNA in the A site to the aminoacyl-tRNA in the P site.
B)The P site is occupied by peptidyl-tRNA carrying the growing polypeptide chain.
C)Binding of mRNA by the small subunit is followed by association of a particular initiator aminoacyl-tRNA that recognizes the first codon.
D)The new,longer peptidyl-tRNA moves from the A site into the P site as the ribosome moves one codon further along the mRNA.

Question 38

The central domain of the 30S ribosomal subunit serves as the decoding centre.What is it composed of?

A)5S rRNA
B)16S rRNA
C)23S rRNA
D)50S rRNA

Question 39

What is the ribosomal peptidyl transferase transformed into by the termination signal complex?

A)a lyase
B)an isomerase
C)a hydrolase
D)a transferase

Question 40

Which of the following is NOT an anatomical characteristic of the 30S subunit of E.coli ribosomes?

A)"head"
B)"body" or "base"
C)"platform"
D)"legs"

Question 41

Which of the following is NOT classified as a GTP-binding protein?

A)30S rRNA
B)EF-Tu
C)EF-G
D)RF-3

Question 42

Which of the following is NOT a dominant mechanism for control of eukaryotic peptide chain initiation?

A)allosteric regulation
B)cofactor availability control
C)phosphorylation/dephosphorylation
D)competitive inhibition

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)cycloheximide
D)tetracycline

Question 44

Diphtheria toxin is extremely potent and only a few micrograms cause death.What is its mechanism of action?

A)It inhibits f-Met-tRNAimet binding.
B)It inhibits translocation of peptidyl-tRNA.
C)It is an enzyme and can catalytically modify a number of GTP-dependent enzymes.
D)It catalyzes inactivation of 28S tRNA.

Question 45

Which of the following is NOT a role for IF-3 during the initiation of translation in prokaryotic cells?

A)It binds to the 30S subunit and is required for the binding of the mRNA to this subunit.
B)Its association with the 30S subunit prevents association with the 50S subunit.
C)Its dissociation from the 30S subunit permits formation of the initiation complex for translation.
D)It binds the 70S subunit to promote binding of a new mRNA.

Question 46

Which of the following is NOT a difference between prokaryotic and eukaryotic protein synthesis?

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 initiations differ significantly in mechanism and process.
D)Prokaryotic termination involves 1 release factor,while eukaryotic termination involves 3.

Question 47

Which of the following can be considered active with respect to the initiation of protein synthesis?

A)intact 70S
B)free 50S
C)free 30S
D)mRNA-bound 30S

Question 48

Which of the following is a protein synthesis inhibitor that catalytically inactivates 28S rRNA and is very toxic in eukaryotic cells?

A)ricin
B)puromycin
C)cycloheximide
D)tetracycline

Question 49

Which of the following is NOT a characteristic of eukaryotic mRNA?

A)poly(A)tail
B)no Shine-Dalgarno sequence
C)codon binding directs for an initiator tRNA carrying met
D)5'-7methyl-GTP cap