Chapter 30—Protein Synthesis
MULTIPLE CHOICE
1. 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.
2. 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.
3. 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
4. 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.
5. 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.
6. 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.
7. 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
8. 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.
9. 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.
10. 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
11. 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.
12. 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.
13. 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
14. 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
15. ____ 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
16. ____ are the agents of protein synthesis.
a.
Nuclei
b.
Mitochondria
c.
Chloroplasts
d.
Ribosomes
e.
Plasma membranes
17. 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
18. 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
19. Ribosomes constitute about ____ of the dry cell mass of an E. coli cell.
a.
1%
b.
5%
c.
10%
d.
20%
e.
40%
20. 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
21. 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.
22. 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
23. 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.
24. Mitochondrial and chloroplastic ribosomes resemble ____ ribosomes.
a.
prokaryotic
b.
lower eukaryotic
c.
higher eukaryotic
d.
no other
e.
none are true
25. 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
26. 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
Garrett/Grisham 5e Test Bank 6
27. 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.
28. Protein synthesis in bacterial cells usually starts with a:
a.
methionine residue.
b.
formylmethionine residue.
c.
cysteine residue.
d.
valine residue.
e.
phenylalanine residue.
29. 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.
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
31. 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
32. 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.
33. 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.
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
35. 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.
36. 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
37. “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
38. 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.
39. The termination signal complex transforms the ribosomal peptidyl transferase into a/an:
a.
lyase.
b.
isomerase.
c.
hydrolase.
d.
transferase.
e.
ligase.
40. 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
41. 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.
42. 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
43. 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.
44. 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.
45. 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
46. 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.
47. 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
48. 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.
49. 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.
50. 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
51. 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
52. 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
53. 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