Deck 22: Protein Synthesis

Question 1

Which statement is not true about the "wobble" position?

A)It is in the 5' 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 3' position of the codon.

Answer 1

Often has inosinate at the 3' position of the codon.

Question 2

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

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

Answer 2

3

Question 3

________ carries the anticodon.

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

Answer 3

tRNA

Question 4

The anticodon of tRNAala can bind to three different codons for alanine (GCU,GCC and GCA)because

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

Question 5

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

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

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

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

A)GGGGCTCTC
B)CTCTCGGGG
C)CCCCGAGAG
D)GAGAGCCCC

Question 8

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 9

The acceptor stem of tRNA consists of the ________.

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

Question 10

The 5' end and the region near the 3' end of tRNA molecules are base-paired to each other forming

A)the anticodon arm.
B)the acceptor or amino acid stem.
C)one arm of the three-dimensional structure.
D)the variable arm.

Question 11

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

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

Question 12

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 13

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

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

Question 14

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 15

Amino acids are attached to tRNA at the ________.

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

Question 16

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 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

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

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

Question 19

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 20

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 21

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

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

Question 22

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 23

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 24

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 25

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 26

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 27

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 28

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 29

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 initiator codon and plays a role in initiation.
C)Anti-Shine-Dalgarno sequence - pyrimidine-rich stretch at the 3' end of 16S rRNA.
D)Eukaryotic initiation factors - IF-1,IF-2,IF-3.

Question 30

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

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

Question 31

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 32

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

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

Question 33

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 5' 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 34

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 35

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

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

Question 36

High levels of ribosome synthesis are maintained in prokaryotes and eukaryotes by ribosomal genes that have

A)clustering in the nucleolus.
B)strong promoters.
C)multiple copies.
D)Both B and C above.

Question 37

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

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

Question 38

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 39

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 40

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 41

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-tRNAfmet from the complex
C)moving the mRNA along one codon
D)All of the above
E)None of the above

Question 42

What provides most of the energy needed for protein synthesis?

A)Breakage of phosphate ester bonds.
B)Breakage of phosphoanhydride bonds.
C)Formation of phosphate ester bonds.
D)Formation of phosphoanhydride bonds.
E)Formation of peptide bonds.

Question 43

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 44

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 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

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

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

Question 47

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 48

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 49

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 50

Which statement is true about the release factors in the termination of translation in E.coli?

A)The release factors methylate the termination codon which blocks the codon from being recognized by a tRNA.
B)The release factors induce conformational changes at the A and P sites of the ribosome that cause the termination of translation.
C)After recognizing the termination codon,the release factors cause the hydrolysis of the peptidyl-tRNA.
D)The release factors are modulators that bind to the ribosomal subunits and cause them to dissociate from each other.

Question 51

During protein synthesis the peptide bond is formed by

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

Question 52

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

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

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

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 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

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 58

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 59

How are the termination codons different from other codons?

A)They contain thymines.
B)The termination codon always codes for methionine.
C)They are not recognized by any tRNA molecules.
D)Their conformations do not allow them to fit properly in the A site of the ribosome.

Question 60

Which statement is false about the energy changes during the course of protein synthesis?

A)Breakage of phosphoanhydride bonds releases energy.
B)Conformational changes in the translational machinery consume energy.
C)Conversion of nucleotide triphosphates to nucleotide mono- or diphosphates releases energy.
D)The loss of entropy due to the ordering of amino acids to form a protein releases energy.
E)None of the above statements is false.They are all true.

Question 61

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 62

Most mature mRNA transcripts contain multiple reading frames.

Question 63

Formation of disulfide bonds,phosphorylation,acetylation and removal of N-terminal residues are all examples of

A)pretranslational modifications.
B)cotranslational modifications.
C)posttranslational modifications.
D)Both B and C above.

Question 64

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

Question 65

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

Question 66

Aminoacyl-tRNA synthetase must catalyze the attachment of the correct amino acid to the correct tRNA if protein synthesis is to be accurate.

Question 67

The genes for rRNA tend to have very strong promoters.

Question 68

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

Question 69

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 70

The ribosome cannot distinguish initiator AUG codons from internal methionine AUG codons.

Question 71

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

Question 72

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 73

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

Question 74

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

Question 75

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

Question 76

The anticodon is found on the variable arm of tRNA.

Question 77

The processing of ribosomal RNA precursors includes binding of six or seven ribosomal proteins before assembly of the ribosome begins.

Question 78

The ribosome distinguishes the initiator AUG codon from other AUG codons that specify methionine residues internally in a protein because there are Shine-Dalgarno sequences just upstream from initiator codons and not upstream of internal methionine codons.

Question 79

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

Question 80

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

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