Deck 22: Protein Synthesis

Question 1

If the anticodon on tRNA is GTC tyrosine)5ʹ → 3ʹ), the sequence of the 5ʹ → 3ʹ template strand of the gene in DNA that specifies this amino acid is

A) AUG.
B) TAC.
C) GTC.
D) CTG.

Answer 1

GTC.

Question 2

Amino acids are attached to tRNA at the .

A) anticodon region
B) 5ʹ end
C) 3ʹ end
D) variable arm

Answer 2

3ʹ end

Question 3

What is the 5ʹ → 3ʹ anticodon for an amino acid with the codon CAG?

A) GAC
B) CUG
C) GUC
D) CTG

Answer 3

CUG

Question 4

Use the table below to determine which template strand DNA sequence written in the 5ʹ → 3ʹ direction) specifies the tripeptide with the sequence gly-ala-leu.

A) GGGGCUCUC
B) CUCUCGGGG
C) CCCCGAGAG
D) GAGAGCCCC

Question 5

The acceptor stem of tRNA consists of the .

A) loop that includes the anticodon
B) terminal CCA only
C) 5ʹ end and a region near the end 3ʹ end that are base-paired to each other
D) variable arm and the D arm

Question 6

The initiation codon .

A) specifies uracil
B) specifies methionine
C) binds a protein complex that starts translation
D) is part of the TATA box

Question 7

Different tRNA molecules that bind the same amino acid are called tRNA molecules.

A) synonymous
B) complementary
C) homologous
D) isoacceptor

Question 8

carries the anticodon.

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

Question 9

The codon for the amino acid specified by the anticodon at the anticodon arm of tRNA is covalently linked to tRNA at the

A) variable arm.
B) D arm.
C) TyC arm.
D) acceptor arm.

Question 10

At the ribosome, the codon and anticodon associate by .

A) hydrogen bonding
B) disulfide bonds
C) ionic attractions
D) covalent bonding
E) hydrophobic interactions

Question 11

Of all the possible triplet codons, do not code for an amino acid.

A) 0
B) 1
C) 2
D) 3
E) 4

Question 12

Different codons that specify the same amino acid are called codons.

A) synonymous
B) repetitive
C) variable
D) multiplex

Question 13

The anticodon of tRNA^ala can bind to three different codons for alanine GCU, GCC and GCA) because

A) there are different bases at the 5ʹ end position of the anticodon.
B) there are different bases at the 3ʹ end position of the anticodon.
C) the base at the 5ʹ position of the anticodon is I and is the wobble position.
D) the base at the 3ʹ position of the anticodon is I and is the wobble position.

Question 14

How many possible codons of normal size) are possible using the bases found in DNA?

A) 4
B) 16
C) 20
D) 64

Question 15

Which is not true about the genetic code?

A) Some amino acids share the same codon.
B) The first two nucleotides of a codon are often enough to specify a given amino acid.
C) Some codons do not specify an amino acid.
D) Nearly all organisms use the same genetic code.

Question 16

What is a reasonable number of nucleotides in a tRNA molecule?

A) 20
B) 80
C) 500
D) 1000
E) The number of nucleotides in tRNA molecules varies by several orders of magnitude, depending on the species.

Question 17

Which statement is true about the number of initiation and STOP codons?

A) One initiation codon; one STOP codon
B) One initiation codon; multiple STOP codons
C) Multiple initiation codons; one STOP codon
D) Multiple codons for both initiation and STOP

Question 18

Which statement is not true about the ʺwobbleʺ position?

A) It is in the 5ʹ position on the anticodon.
B) Base pairing other than Watson-Crick base pairing is allowed at this position.
C) It allows anticodons to recognize more than one codon.
D) Often has inosinate at the 3ʹ position of the codon.

Question 19

The reading frame of DNA is fixed by

A) mRNA.
B) the initiation codon.
C) one of three stop codons.
D) the codon UUU.

Question 20

The unambiguity and degeneracy of the genetic code can best be respectively exemplified by which of the following?

A) UUU and UUC both code for Phe; UUU codes only for Phe
B) UUU codes only for Phe; UUU and UUC both code for Phe
C) UUU codes for both Phe and Ser; UUU and UUC both code for Phe and Ser
D) UUU and UUC both code for Phe and Ser; UUU codes for both Phe and Ser

Question 21

Which statement is false concerning aminoacyl-tRNA synthetase?

A) It recognizes only one amino acid, but may recognize more than one tRNA.
B) It requires a conversion from ATP to ADP.
C) Hydrolysis of pyrophosphate essentially makes its reaction irreversible.
D) Some synthetases bind the anticodon and others do not.

Question 22

Which is true about proofreading activity during the synthesis of aminoacyl-tRNAs?

A) Proofreading is accomplished as an amino acid enters the active site of the enzyme. Incorrect amino acids are rejected before any reaction occurs.
B) Proofreading occurs just after aminoacyl-adenylate formation.
C) A separate cytosolic proofreading enzyme catalyzes the hydrolysis of incorrect aminoacyl-tRNAs.
D) No proofreading activity is necessary due to the high level of specificity of all aminoacyl-tRNA synthetases.

Question 23

Chain elongation consists of three steps: 1) positioning the correct aminoacyl-tRNA to the A site, 2) forming the peptide bond and 3) .

A) dissociation of the 30S and 50S subunits
B) removal of the fMet-tRNA_f^met from the complex
C) moving the mRNA along one codon
D) All of the above
E) None of the above

Question 24

Which statement is false about polysomes?

A) They consist of mRNA and many translation complexes that are separated by about 100 nucleotides.
B) They serve to amplify the information contained in mRNA many-fold.
C) The number of translation complexes one contains depends on the efficiency of initiation.
D) They do not occur in prokaryotes.

Question 25

The first amino acid incorporated into proteins .

A) can be any of the 20 standard amino acids
B) is an N-formylmethionine in E. coli and methionine in other organisms
C) is always inosinate
D) is an amidated methionine residue that is cleaved following termination of translation

Question 26

Which help cells avoid mis-insertion of amino acids in protein synthesis?

A) the specificity of codon:anticodon interactions
B) the specificity of tRNA: amino acid pairs
C) the proofreading ability of tRNA synthetases
D) All of the above

Question 27

How many GTP are hydrolyzed for every aminoacyl-tRNA that is successfully inserted into the A site of the ribosome?

A) zero
B) 1
C) 2
D) 4

Question 28

The deaminoacylated tRNA leaves the ribosome as the growing polypeptide passes through the tunnel of the large ribosomal subunit from the .

A) 30S or 40S subunit
B) protein factors
C) E site
D) P site

Question 29

At the end of the initiation step, the ribosome has a vacant

A) A site.
B) P site.
C) mRNA site.
D) tRNA.
E) All of the above

Question 30

Which statement is false concerning ribosomes and their components?

A) All ribosomes have two subunits of unequal size.
B) The genes for eukaryotic rRNA occur as tandem arrays of hundreds of copies.
C) The 30S and 50S ribosomal subunits of E. coli combine to generate an 80S subunit.
D) Sequences exist in prokaryotic and eukaryotic rRNA that are so similar, they likely derive from a common ancestor.

Question 31

The net effect of all amino acid tRNA synthetases binding to a tRNA is to position the of tRNA in the active site.

A) 3ʹ end
B) 5ʹ end
C) anticodon
D) D arm

Question 32

In eukaryotes what is the function of eIF-4 cap binding protein)?

A) It assists in the dissociation of the ribosomal complex following termination of translation.
B) It cleaves the first amino acid on a newly translated protein.
C) It binds to the 5ʹ end of mRNA and assists in the formation of the pre-initiation complex.
D) It acts as a general acid-base catalyst during the formation of the peptide bond.

Question 33

Shifting of the reading frame by one nucleotide results in .

A) the production of a completely different protein that is likely non-functional
B) a substitution only at the first amino acid
C) the generation of homologous proteins
D) a protein that has one less or one more amino acid

Question 34

Which of the following is mismatched?

A) initiator tRNA - recognizes AUG codons during initiation at the P site
B) Shine-Dalgarno sequence - upstream of the initator codon and plays a role in initiation
C) Shine-Dalgarno sequence - pyrimidine-rich stretch at the 3ʹ end of 16S rRNA
D) eukaryotic initiation factors - IF-1, IF-2, IF-3

Question 35

At the ribosome the template mRNA is translated in the direction, while the protein is synthesized in the direction.

A) 5ʹ → 3ʹ; N-terminal to C-terminal
B) 5ʹ → 3ʹ; C-terminal to N-terminal
C) 3ʹ → 5ʹ; N-terminal to C-terminal
D) 3ʹ → 5ʹ; C-terminal to N-terminal

Question 36

The correct order for the formation of the prokaryotic 70S initiation complex is

A) 50S → IF-1, IF-2 → mRNA → fMet-tRNA_f^met → 30S
B) 30S → IF-1, IF-3 → fMet-tRNA_f^met → IF-2 → mRNA → 50S
C) 30S → IF-1, IF-3 → IF-2 → fMet-tRNA_f^met → mRNA → 50S
D) 30S → IF-1, IF-2 → IF-3 → fMet-tRNA_f^met → mRNA → 50S

Question 37

The link between an activated amino acid and tRNA is an bond between the of the amino acid and a hydroxyl group of the tRNA.

A) ester; carboxylate group
B) amide; carboxylate group
C) amide; amino group
D) imine; amino group

Question 38

After the action of peptidyl transferase, the peptidyl-tRNA is located at the

A) P site.
B) A site.
C) E site.
D) partly in the A site and partly in the P site.

Question 39

Prokaryotic mRNA molecules that contain several coding regions that encode several polypeptides are .

A) synonymous
B) tandemly coded
C) polycistronic
D) impossible

Question 40

What statement is not true about the Shine-Dalgarno sequence?

A) It is a pyrimidine-rich region of mRNA.
B) It is present only in prokaryotes.
C) It is complementary to a sequence of an rRNA sequence.
D) It helps position the initiation codon at the P site on the ribosome.

Question 41

Ribosomal protein synthesis is controlled by inhibitor proteins, the genes of which are located on the ribosomal protein operon, and which bind to when ribosome assembly slows and bind to when ribosome assembly is proceeding at a steady rate.

A) rRNA; mRNA
B) 30S; 50S
C) 50S; 30S
D) mRNA; rRNA
E) 50S; mRNA

Question 42

Unlike bacterial mRNA, eukaryotic mRNA must undergo before it may be used for translation.

A) splicing
B) capping
C) polyadenylation
D) export to the cytoplasm
E) All of the above

Question 43

Tryptophan synthesis can be controlled by a process called attenuation in which the levels of tryptophan in the cell control translation by

A) the binding of the RNA polymerase to the genome.
B) the alteration of the repressor protein.
C) the folding of mRNA into hairpin loops.
D) genes rich in codons for tryptophan.

Question 44

Arrange the events listed below in order according to the signal hypothesis: I. Signal sequence binds to SRP
II. Translation stops
III. Translation starts
IV. Ribophorins anchor complex
V. SRP dissociates; GTP hydrolyzed
VI. SRP-signal complex binds to docking protein

A) I → II → II → IV → V → VI
B) I → III → VI → V → II → IV
C) V → III → IV → VI → II → I
D) I → II → VI → IV → III → V

Question 45

The role of EF-Tu in bacterial protein synthesis is

A) formation of the peptide bond.
B) positioning the correct aminoacyl-tRNA at the A site.
C) positioning the correct aminoacyl-tRNA at the P site.
D) moving the mRNA by one codon.
E) All of the above

Question 46

Termination stop codons are recognized by specific proteins that cause newly synthesized peptides to be released from the ribosome.

Question 47

Which statement is true about the attenuation mechanism of regulation?

A) Eukaryotes lack this mechanism because transcription and translation occur in different parts of the cell.
B) Attenuation is the modern term for repression in prokaryotes.
C) It is a form of regulation at the level of transcription, thereby preventing any translation.
D) Attenuation is the most common type of regulation found in plants.

Question 48

For each amino acid added to a polypeptide chain, phosphoanhydride bonds are cleaved.

A) 1
B) 2
C) 3
D) 4
E) 5

Question 49

The E site on the ribosome is the location of

A) EF factors.
B) a tunnel in the ribosome.
C) the deaminoacylated tRNA.
D) the aminoacylated tRNA.
E) None of the above

Question 50

In prokaryotes the codons can be arranged in an overlapping fashion. In eukaryotes they are arranged only in a non-overlapping fashion.

Question 51

When an oligosaccharide is covalently bonded to an asparagine or other amino acid) side chain, the resulting product is an)

A) protein glycoside.
B) glyocophorin.
C) glycoprotein.
D) oligoprotein.

Question 52

Tryptophan synthesis is controlled by a repressor protein which is activated by a corepressor which is

A) leader peptide.
B) promoter locus.
C) operator locus.
D) tryptophan.

Question 53

Translation begins to be terminated when

A) three release factors appear at the ribosome complex.
B) three release factors enhance the hydrolysis of the peptide.
C) an fMet tRNA codon is in the mRNA.
D) a termination codon is in the mRNA.
E) the ribosomal subunits dissociate from the mRNA.

Question 54

At the beginning of translocation, the growing peptide chain is attached to tRNA located at the on the ribosome.

A) P site and part of the A site
B) A site and part of the P site
C) A site only
D) P site only

Question 55

The role of GTP in the translocation step of protein synthesis is to supply energy for

A) peptide bond formation.
B) dissociation of EF-G-GDP.
C) movement of the peptidyl-tRNA from the P site to the A site.
D) movement of the peptidyl-tRNA from the A site to the P site.
E) None of the above

Question 56

An elongation factor EF-Ts serves mainly to

A) hydrolyze GTP.
B) exchange GTP for GDP.
C) eeliver the aminoacyl-tRNA to the ribosome.
D) hydrolyze GDP.
E) All of the above

Question 57

Puromycin is an antibiotic that inhibits protein synthesis because

A) it binds a ribosomal protein.
B) it inhibits peptidyl transferase.
C) it binds to the 50S subunit preventing translocation.
D) it looks like aminoacyl-tRNA and binds to the A site.
E) it binds to the E site.

Question 58

The peptide bond is formed by

A) a protein-catalyzed reaction.
B) an RNA-catalyzed reaction.
C) a combination of A and B.
D) hydrolysis of ATP.
E) hydrolysis of CTP.

Question 59

If there is more globin than heme present in a reticulocyte, globin synthesis is stopped by

A) the activation of HCI heme-controlled inhibitor).
B) the inactivation of HCI.
C) increasing heme synthesis.
D) decreasing heme synthesis.
E) activating eIF-2.

Question 60

The role of GTP in the elongation phase of protein synthesis is to supply energy for

A) peptide bond formation.
B) formation of aminoacyl-tRNA molecules.
C) movement of mRNA along the ribosome.
D) changing the configuration of EF-Tu-GTP.
E) All of the above

Question 61

Coupling of transcription and translation occurs in both animal and bacterial cells.

Question 62

More energy is used to form a single peptide bond than is required for the bond formation alone.

Question 63

Streptomycin can be used clinically because it inhibits bacterial protein synthesis but not eukaryotic protein synthesis.

Question 64

Release factors fit into the A site when one of three codons UGA, UAG, or UAA is positioned there.

Question 65

Chaperone proteins help to fold newly translated proteins into correct configurations.

Question 66

The EF-Tu-GTP complex recognizes fMet-tRNA_f^met in bacteria but not in eukaryotic cells.

Question 67

Class II aminoacyl-tRNA synthetases are often multimeric enzymes that do not bind to the anticodon.

Question 68

Most mature mRNA transcripts contain multiple reading frames.

Question 69

The main control of the rate of globin synthesis is due to the activity of GEF guanine nucleotide exchange factor.

Question 70

There are five times more ribosomes in eukaryotic cells than in most bacterial cells.

Question 71

Methionine and tryptophan are the only amino acids that do not have multiple codons.

Question 72

EF-Ts promotes the dissociation of GDP from the EF-Tu-GDP complex to recycle this elongation factor.

Question 73

Puromycin can be used clinically because it inhibits bacterial protein synthesis by resembling aminoacyl-tRNA.

Question 74

Translation at the ribosomes of eukaryotes is usually a much faster process than DNA replication.

Question 75

Inosinate (I) is an acetylated form of G and it can base-pair with A, C, or U.

Question 76

Isoacceptor tRNAs can only differ in primary sequence at the anticodon.

Question 77

In eukaryotes the initiation codon is the first AUG triplet from the 5ʹ end of mRNA.

Question 78

The anticodon is found on the variable arm of tRNA.

Question 79

Peptidyl transferase catalyzes peptide bond formation, and the activity is contained within the protein portion of the large ribosomal subunit.

Question 80

The genes for rRNA tend to have very strong promoters.