Deck 22: Protein Synthesis, Posttranslational Modification, and Transport

Question 1

The tRNA 3 ^' $\rightarrow$ 5 ^' anticodon loop that recognizes the 5 ^' $\rightarrow$ 3 ^' codon UCC could have the sequence

A) AGG.
B) GGA.
C) UCC.
D) CCU.

Answer 1

AGG.

Question 2

In yeast, the number of tRNA genes is __________ the number of _.

A) equivalent to; amino acids
B) less than; amino acids
C) equivalent to; mRNAs
D) greater than; codons

Answer 2

less than; amino acids

Question 3

Consider an in vitro experiment in which all components needed for protein synthesis are present. If tRNAs charged with radioactively labeled amino acids are added, over time the radioactivity would be located in which of the following components?

A) mRNA
B) aminoacyl tRNA synthetase
C) nascent protein
D) codons

Answer 3

nascent protein

Question 4

How many potential codons does the following mRNA sequence contain?

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

Question 5

Inosine is formed through a

A) deamination of adenosine.
B) deamination of cytosine.
C) demethylation of thymine.
D) deamination of guanosine.

Question 6

Where would an amino acid be attached to the tRNA below?

A) A
B) B
C) C
D) D

Question 7

The anticodon of tRNA is made up of bases.

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

Question 8

The adaptor molecule in translation is

A) aminoacyl-tRNA synthetase.
B) mRNA.
C) rRNA.
D) tRNA.

Question 9

Which molecule contains both an amino acid acceptor stem and an anticodon?

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

Question 10

tRNA must be before binding to the ribosome to allow for translation to occur.

A) charged with a codon
B) charged with an anticodon
C) charged with an amino acid
D) bound by ATP

Question 11

Which component of the Nirenberg-Leder experiment, that assigned triplet codons to specific amino acids, was radioactively labeled?

A) ribosome
B) aminoacyl-tRNA
C) tRNA
D) mRNA

Question 12

Which of the following is considered the adaptor molecule in protein synthesis?

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

Question 13

Which base location in the figure below is LEAST discriminating in the bases that it can pair with as described by the wobble hypothesis?

A) A
B) B
C) C
D) D

Question 14

An analysis of noncanonical base pairings between the 5 ^' -position of the tRNA anticodon and the 3 ^' -position of the mRNA codon would show the pairing

A) I-G.
B) G-A.
C) I-U.
D) I-I.

Question 15

The wobble hypothesis was first proposed by

A) Leder.
B) Nirenberg.
C) Holley.
D) Crick.

Question 16

What region of the amino acid below would become covalently attached to a tRNA?

A) A
B) B
C) C
D) D

Question 17

Noncanonical base pairings are observed between the third position of the codons and the first position of the anticodons. This concept is known as the

A) nonsense rule.
B) noncanonical hypothesis.
C) wobble hypothesis.
D) 3:1 hypothesis.

Question 18

Which of the following mRNA codons would NOT be recognized by a tRNA that is charged with an amino acid?

A) CAA
B) GUU
C) CUC
D) UAA

Question 19

Noncanonical base pairings of A and I would contain hydrogen bonds. The base pairing of C and I would contain hydrogen bonds.

A) 1; 3
B) 1; 2
C) 2; 2
D) 2; 1

Question 20

If the following mRNA was added to a cell-free translation system, how many unique protein sequences would be generated?

A) 14
B) 7
C) 2
D) 3

Question 21

Where might the molecule shown below be located in both the prokaryotic and eukaryotic ribosome?

A) A site
B) E site
C) 40S complex
D) 70S complex

Question 22

tRNAs interact with the ribosome only after

A) they bind the free mRNA.
B) the small and large subunits have come together.
C) the first peptide bond in the nascent chain is formed.
D) the AUG start codon is positioned in the E site.

Question 23

The Shine-Dalgarno sequence of mRNA base pairs with the rRNA within the prokaryote __________ ribosomal subunit.

A) 23S; 30S
B) 16S; 50S
C) 16S; 30S
D) 5S; 50S

Question 24

Different tRNAs for the same amino acid that bind alternate codons are known as tRNAs.

A) cognate
B) isoacceptor
C) variable
D) class I and class II

Question 25

Eukaryotes are directed to begin scanning the mRNA for the start codon based on binding of the

A) Shine-Dalgarno sequence.
B) poly(A) tail and 5 ^' cap.
C) Met-tRNA_i^fMet.
D) 16S rRNA.

Question 26

Which of the following catalyzes the formation of a bond between an amino acid and a tRNA?

A) aminoacyl-tRNA synthetase
B) aminoacyl-tRNA hydrolase
C) tRNA linking enzyme
D) ribosome

Question 27

In an iteration of the Nirenberg-Leder experiment to assign triplet codons to specific amino acids, radioactively labeled aminoacyl-tRNA with the anticodon of CUG was used. The radioactivity was retained on the filter at the end of the experiment. Which mRNA was used in this iteration of the experiment?

A) CAG
B) GAC
C) CTG
D) GTC

Question 28

tRNA interacts with ribosomes at one of three sites: the E site, the P site, and the site.

A) T
B) M
C) SD
D) A

Question 29

Below are examples of sequences from seven different E. coli genes. The underlined sequences are known as sequences and the bolded AUG sequences are known as the codon.

A) Shine-Dalgarno; start
B) Shine-Dalgarno; S
C) initiation factor; start
D) initiation factor; S

Question 30

Aminoacyl-tRNA synthetases carry out editing

A) before activation of amino acid with ATP.
B) at a site that is distinct from the active site.
C) at the same time that the amino acid is transferred to the 3 ^' group.
D) by binding to an editing subunit.

Question 31

What characteristics of eukaryotic mRNA are recognized through specific interactions during the formation of the translation initiation complex?

A) 3 ^' cap
B) Shine-Dalgarno sequence
C) poly(A) tail
D) GTP-binding site

Question 32

A full catalytic cycle of an aminoacyl-tRNA synthetase generates __________ as a product.

A) ATP
B) ADP
C) H₂O
D) AMP

Question 33

The prokaryotic ribosome contains __________ subunits. The eukaryotic ribosome contains __________ subunits.

A) 30S and 70S; 40S and 60S
B) 40S and 60S; 30S and 80S
C) 30S and 50S; 40S and 60S
D) 30S and 60S; 40S and 50S

Question 34

Prokaryotic mRNA will directly interact with __________ during translation.

A) release factors
B) 23S rRNA
C) Kozak sequence
D) GTP

Question 35

The eukaryotic 48S preinitiation complex is purified and the components are identified. Which of the following would be found in this complex?

A) 60S ribosomal subunit
B) Met-rRNA^Met
C) EF-Tu
D) eIF4

Question 36

All aminoacyl-tRNA synthetases are

A) monomeric.
B) tetrameric.
C) able to bind ATP.
D) able to bind ADP.

Question 37

What is the identity of the protein labeled with the question mark in the eukaryotic preinitiation complex shown below?

A) PABP
B) eIF5B
C) eIF4E
D) eIF2

Question 38

Ribosomal rRNA interacts with all EXCEPT during the process of translation.

A) mRNA
B) tRNA
C) ribosomal proteins
D) PABP

Question 39

A common feature of translation in both eukaryotes and prokaryotes is

A) hydrolysis of ATP to facilitate translocation of the ribosome.
B) hydrolysis of GTP to promote binding of the AA-tRNA^AA.
C) a P site that can contain uncharged tRNA.
D) an E site that can contain a tRNA covalently bound to a nascent polypeptide.

Question 40

Both prokaryotes and eukaryotes recognize __________ as a start codon.

A) AUG
B) UAC
C) GUA
D) CAU

Question 41

A newly discovered protein is found to be modified by a lipid. Where is this protein most likely located?

A) nucleus
B) proteasome
C) cell membrane
D) extracellular matrix

Question 42

Which antibiotic functions by inhibiting cell wall synthesis?

A) penicillin
B) linezolid
C) tetracycline
D) rifampin

Question 43

If a protein is covalently modified by ubiquitin, it will be

A) degraded.
B) secreted.
C) targeted to the nucleus.
D) anchored to the plasma membrane.

Question 44

A nucleophilic amino group of the amino acid bound to the 3 ^' terminus of A-site tRNA attacks the electrophilic carbonyl carbon in the ester bond between the 3 ^' terminus of P-site tRNA and its bound amino acid during the step of translation.

A) initiation
B) elongation
C) translocation
D) termination

Question 45

After the initiation complex is complete, what occurs next in the process of translation?

A) peptide bond formation
B) EF-G•GTP binding
C) EF-Tu•GTP AA-tRNA^AA binding
D) RF2 binding

Question 46

Release factor hydrolyzes GTP during the __________ step of translation.

A) initiation
B) elongation
C) translocation
D) termination

Question 47

Gene expression can be controlled by the modification of histones by all of the following EXCEPT

A) phosphorylation.
B) methylation.
C) acetylation.
D) glycosylation.

Question 48

In the image below, which group will be attacked by the nucleophilic amino group of the next amino acid brought into the ribosome?

A) A
B) B
C) C
D) D

Question 49

Place the following steps in the initiation phase in a prokaryote in their proper order.
A. mRNA binds to the complex.
B. GTP is hydrolyzed.
C. IF1, IF2, and IF3 bind the 30S subunit.

A) C; B; A
B) C; A; B
C) A; B; C
D) B; C; A

Question 50

Place the following steps in the elongation phase of translation in their proper order.
A. Peptide bond formation occurs.
B. GTP is hydrolyzed, and the ribosome moves one codon in the 3 ^' direction.
C. GTP is hydrolyzed, and EF-Tu•GDP is released.
D. tRNA is released from the E site.

A) A; C; B; D
B) A; B; C; D
C) B; D; C; A
D) C; A; B; D

Question 51

Which of the following is NOT a component that is released from the ribosome on translation termination?

A) RF2
B) nascent polypeptide
C) tRNA
D) Met-tRNA^fMet

Question 52

Enzyme-mediated protein modification in eukaryotic cells is a means of regulating the activity of the protein. Which of the following is UNLIKELY to result from such a modification?

A) phosphorylation
B) methylation
C) glycosylation
D) hydration

Question 53

Which antibiotic would be a good choice to use as a research tool if investigating the role of DNA gyrase in a cell?

A) coumermycin
B) penicillin
C) tetracycline
D) bacitracin

Question 54

In the ER, prenylation can occur. Prenylation is the attachment of an isoprenoid group to a __________ residue via a(n) _.

A) lysine; amide
B) cysteine; thioester
C) threonine; ester
D) serine; ester

Question 55

Which antibiotic functions by inhibiting DNA gyrase?

A) vancomycin
B) coumermycin
C) aminoglycosides
D) clindamycin

Question 56

Secondary downstream of the cap structure in the mRNA is unwound during the step of translation.

A) initiation
B) elongation
C) translocation
D) termination

Question 57

All glycoproteins have __________ covalently added posttranslationally.

A) carbohydrates
B) phosphates
C) methyl groups
D) acetyl groups

Question 58

How many GTP are hydrolyzed during a single round of translation elongation in a eukaryote?

A) 0
B) 1
C) 2
D) 6

Question 59

An experiment with bacteria that has been exposed to an antibiotic reveals that the translocation step has been inhibited. Which antibiotic was likely used?

A) chloramphenicol
B) erythromycin
C) tetracycline
D) streptomycin

Question 60

The antibiotics streptomycin, tetracycline, and chloramphenicol all interfere with

A) cell membrane formation.
B) protein synthesis.
C) nucleic acid synthesis.
D) cell wall formation.

Question 61

A protein is targeted to the plasma membrane. Its final functional location is as a subunit of a transmembrane protein that interacts with the central subdomain of the membrane. Analysis of this protein would most likely show modification with a

A) myristoylate.
B) palmitoylate.
C) isoprenoid.
D) phosphate.

Question 62

Which sequence is MOST likely to be modified with the fatty acid myristoylate in the ER? (The … represents additional amino acids N-terminal to those shown.)

A) Cys-Leu-Ala-Ile-Ser-Phe…
B) Leu-Gly-Phe-Ala-Ser-Phe…
C) Gly-Leu-Phe-Ala-Ile-Ser…
D) Phe-Leu-Cys-Gly-Leu-Ile…

Question 63

A is NOT a characteristic of the ER signal peptide sequence.

A) N-terminal segment containing negatively charged amino acids
B) segment containing hydrophobic amino acids
C) C-terminal segment containing hydrophobic amino acids
D) protease cleavage site

Question 64

An inhibitor of would specifically prohibit the release of Ran from importin.

A) GTP-GDP exchange in Ran
B) exportin
C) the signal peptide peptidase
D) GAP

Question 65

Which protein would initially have been translated on free ribosomes?

A) lysosomal-associated membrane protein 1 (LAMP-1)
B) insulin receptor $\alpha$ subunit
C) collagen
D) histone subunit H2A

Question 66

Aminoacyl-tRNA synthetase contains two binding sites. Describe the consequence of a mutation that changed the specificity of the amino acid binding site of an aminoacyl-tRNA synthetase from Glu to Asp.

Question 67

During the import of one protein from the cytosol to the nucleus via Ran-dependent nuclear import, __________ high-energy phosphate molecule(s) are hydrolyzed.

A) 2 ATP
B) 1 GTP
C) 1 GTP and 1 ATP
D) 2 GTP

Question 68

Why does the genetic code require triplet codons to code for the 20 different amino acids? Why would duplet codons be inadequate to perform the job?

Question 69

At any time during nuclear import and export, Ran can be found associated with all EXCEPT

A) GTP.
B) exportin.
C) GMP.
D) importin.

Question 70

Which of the following sequences is most likely a nuclear localization signal?

A) Lys-Lys-Arg-Gly-Arg
B) Glu-Asp-Asp-Gly-Glu
C) Ile-Leu-Phe-Leu-Gly
D) Lys-Asp-Arg-Glu-Glu

Question 71

How does the wobble hypothesis allow for fewer than 63 tRNAs to effectively recognize 63 codons?

Question 72

Place the following steps in proper order for the translation of a membrane-bound protein.
A. GTP binds to SRP.
B. Protein synthesis occurs on free ribosome.
C. Protein synthesis halts.
D. SRP binds to the signal peptide sequence.

A) A; B; C; D
B) B; D; C; A
C) D; C; B; A
D) A; B; D; C

Question 73

The rate of translation of an identical mRNA sequence is measured in cells from two different species-E. coli and human. It is found that the rate is slower in E. coli cells. What is a possible reason for this finding?

Question 74

Although the genetic code is considered universal, this may not be fully true when comparing the human nuclear code with the human mitochondrial code. Describe how and provide a specific example.

Question 75

Choose the sequence that is MOST likely to be modified with the fatty acid palmitoylate in the ER. (The … represents additional amino acids N-terminal or C-terminal to those shown.)

A) …Phe-Leu-Cys-Gly-Leu-Ile…
B) …Gly-Leu-Phe-Ala-Ile-Ser…
C) …Tyr-Leu-Ala-Ile-Ser-Phe…
D) …Ala-Thr-Leu-Phe-Ser-Gly…

Question 76

What step in the process of translation of a nascent protein into the lumen of the ER requires an input of energy provided by the hydrolysis of GTP?

A) binding of SRP to the signal peptide sequence
B) release of SRP from the ribosome
C) transfer of the signal peptide sequence into the translocon
D) binding of SRP to the SRP receptor

Question 77

Which sequence is MOST likely to contain an O-linked oligosaccharide in the ER? (The … represents additional amino acids N-terminal or C-terminal to those shown.)

A) …Phe-Leu-Cys-Gly-Leu-Ile…
B) …Gly-Leu-Phe-Ala-Ile-Gly…
C) …Tyr-Leu-Ala-Ile-Gly-Phe…
D) …Ala-Thr-Leu-Phe-Ser-Gly…

Question 78

An experimental prep is able to separate the following membrane fractions: nuclear membrane, Golgi apparatus membrane, transport vesicle membrane, and mitochondrial membrane. The membrane fractions can then be analyzed via Western blotting for the presence of specific proteins. Which fraction would indicate the presence of t-SNAREs?

A) nuclear membrane
B) Golgi apparatus membrane
C) transport vesicle membrane
D) mitochondrial membrane

Question 79

Explain what is meant by the statement, "The genetic code is universal."

Question 80

Which sequence is MOST likely to be prenylated in the ER? (The … represents additional amino acids N-terminal to those shown.)

A) …Cys-Leu-Leu-Phe-Ala-Lys
B) …Leu-Phe-Leu-Cys-Ile-Phe
C) …Phe-Ile-Leu-Ser-Ile-Leu
D) …Cys-Leu-Cys-Leu-Lys-Phe