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Operons are a(n) ____________ sequence lying adjacent to the DNA being
transcribed and are composed of a promoter located next to a(n) _______ that
interacts and is controlled by a(n) _______ protein.
A. initiation; operator; repression B. operator; repressor; regulatory
C. regulatory; repressor; activator D. regulatory; operator; regulatory
E. none are true
In prokaryotes, gene expression is often responsive to small molecules where
increasing synthesis of enzymes for metabolism of a certain substrate is
termed ___________ and the substrate is called ___________. Likewise
metabolic products that decrease synthesis of enzymes for their production are
called ________ and carry out ____________.
A. autoregulation; regulatory; co-repressors; initiation
B. co-induction; induction; co-repressors; initiation
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C. induction; co-inducer; co-repressors; repression
D. induction; co-inducer; repressor; co-repression
E. all are true
Expression of genes independently of regulation is termed:
A. negative regulation.
B. constitutive expression.
C. transcription expression. D. repressible regulation. E. autoregulation.
All are components of the lac operon EXCEPT:
A. the structural genes for lacZ, lacY and lacA.
B. the operator and promoter sequences.
C. lacI gene.
D. promoter for the lacI gene.
E. all are correct.
All are lac repressor properties EXCEPT:
A. tetrameric protein expressed constitutively. B. binding site for DNA.
C. binding site for mRNA.
D. binding site for inducer.
E. blocks elongation so initiation is aborted.
Repressible operons are expressed only in the _________ of their co-repressor
and inducible operons are transcribed only in the _____ of _______
co-inducers.
A. absence; presence; small molecule
B. presence; presence; small molecule
C. presence; absence; protein
D. absence; presence; protein
E. absence; absence; cAMP receptor protein
When the cellular level of tryptophan decreases in E. coli:
A. tryptophan-bound Trp repressor associates with trp operator.
B. Trp aporepressor has lowered affinity for trp promoter allowing RNA.
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polymerase binding and transcription of the trp operon.
C. tryptophan binds trp inducer to promote positive control of trp promoter.
D. trp repressor has a greater affinity for trp operator.
E. none of the above.
All are characteristics of control mechanisms that regulate transcription in
prokaryotes EXCEPT:
A.protein : protein interactions are an essential component of transcription
regulation.
B. DNA : protein interactions are central to transcription regulation.
C. regulatory proteins commonly bind DNA at sites of at least partial dyad
symmetry or inverted repeats.
D. regulatory proteins receive cues that signal the status of the environment of
the cell.
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E. all are characteristics.
The recurring structural feature in DNA-binding proteins is the presence of
____________ segments that fit into the _______ grove of B-DNA.
-helix; major
-sheet; major C. -turn; minor
D-barrel; minor E. all are true
The base-pair edges in the ______ groove act as a(n) ____________
identifiable through __________ with specific proteins.
A. minor; enhancer; H-bonding
B. minor; recognition matrix; H-bonding
C. major; recognition matrix; H-bonding
D. major; repressor; ionic binding
E. major; transcriptional silencer; ionic bonding
Lac repressor is an example of the DNA-binding motif common to many
prokaryotic regulatory proteins and is:
A. a homeobox.
B. a zinc finger.
C. a basic region-leucine finger.
D. a helix-turn-helix.
E. none of the above.
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.
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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.
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.
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. they bridge the information gap between amino acids and codons.
E. they must "read" the anticodon of the tRNA.
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.
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
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.
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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.
Mitochondrial and chloroplastic ribosomes resemble ________ ribosomes.
A. prokaryotic
B. lower eukaryotic
C. higher eukaryotic
D. no other
E. none are true
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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
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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
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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
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.
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
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The order of events in the initiation of protein synthesis is:
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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-tRNAifMet 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
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.
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D. binds initiator tRNA and GTP.
E. binds to 30 S subunit and drives mRNA binding.
GTP hydrolysis is essential for all of the following EXCEPT:
A. the formation of the initiation complex (translationally active 70 S
ribosome complex).
B. the elongation step of translation.
C. the translocation step of translation.
D. the binding of release factors to the ribosome.
E. all utilize GTP hydrolysis.
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
“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
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.
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E. displacement of EF-G by EF-Tu:aminoacyl-tRNA.
All are GTP binding proteins EXCEPT:
A. IF-2.
B. EF-Tu.
C. EF-G.
D. RF-3.
E. all are true.
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
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.
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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.
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.
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
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
The primary driving force for folding is _________ 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
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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
All are characteristics of chaperonins EXCEPT:
A. allow folding to proceed in a protected environment.
B. large, cylindrical protein complexes.
C. sequester partially folded proteins.
D. formed of two stacked rings of subunits.
E. all are true.
The folding cycle in the GroES-GroEL complex of E. coli utilizes the
following sequence:
A. ATP binding to GroEL
B. GroES dissociates from the complex
C. Partially folded protein hydrophobic residues bind GroEL
D. GroES is recruited to GroEL
E. GroES promotes ATP hydrolysis and -subunits undergo a conformational
change that buries the hydrophobic patches
A. A, B, C, D, E
B. B, A, C, D, E
C. C, D, A, E, B
D. C, A, D, E, B
E. D, C, E, A, B
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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.
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.
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E. all are characteristics.
______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
Eukaryotic secretory proteins are synthesized and translocated via the
endoplasmic reticulum. Order the following sequence of events for this
process.
A. signal sequence removed.
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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
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
Proteins with _____________ sequences remain embedded in the ER
membrane with their ____-termini on the cytosolic face of the ER.
A. translocator; N
B. leader; C
C. translocational; N
D. stop-transfer; C
E. translocon; N
The proper sequence for transport of inner mitochondrial membrane proteins
would be:
A. TOM; SAM.
B. TOM; TIM23.
C. SAM; TOM; TIM22.
D. TOM; TIM22.
E. SAM; TOM; TIM22.
Protein degradation is compartmentalized either in macromolecular structures
known as ______________ or in degradative organelles such as ___________.
A. ribosomes; endoplasmic reticulum
B. ribosomes; Golgi
C. proteosomes; mitochondria
D. proteosomes; lysosomes
E. lysosomes; endoplasmic reticulum
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The appropriate sequence for ubiquitination of proteins to be degraded is:
A. multiple ubiquitinations may occur on a protein substrate,
B. ubiquitin-protein ligase (E3) transfers ubiquitin to free amino groups on the
protein,
C. E3 selects a protein for degradation by the nature of the N-terminal amino
acid,
D. ubiquitin-carrier protein (E2) picks up ubiquitin,
E. ubiquitin-activating enzyme (E1) attaches via ATP-dependent formation of
thioester bond to C-termini of ubiquitin,
A. A, C, B, D, E
B. E, D, A, B, C
C.
D, E, C, A, B
D. C, E, D, B, A
E. E, D, C, B, A
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In the proteosomes, the 19S cap acts as a ___________ complex for the
recognition and selection of _________ proteins for ________ by the 20S
proteosomes core.
A.
B.
C.
D.
E.
hydrolysis; unfolded; disposal
regulatory; unfolded; disposal
hydrolysis; ubiquitinylated; degradation
regulatory; ubiquitinylated; degradation
all are true