Deck 9: The Molecular Biology of Translation

Question 1

Identification of ribosomal proteins involved two-dimensional gel electrophoresis,which separates the proteins on the basis of

A)mass.
B)folded shape.
C)charge.
D)mass and charge.
E)mass,charge,and folded shape.

Answer 1

D

Question 2

Heinz Fraenkel-Conrat induced point mutations in the coat proteins of TMV and looked for mutations in the resulting proteins.By examining single-base changes in the mRNA,Conrat proved that

A)the genetic code is overlapping.
B)the genetic code is nonoverlapping.
C)the genetic code is redundant.
D)there are 20 amino acids.
E)the genetic code is triplet.

Answer 2

B

Question 3

Elongation factors translocate the ribosome in the 3′ direction by a distance of

A)one codon.
B)one nucleotide.
C)two nucleotides.
D)two codons.
E)three codons.

Answer 3

A

Question 4

What method can be used to separate ribosomal protein subunits?

A)polymerase chain reaction
B)gel electrophoresis
C)two-dimensional gel electrophoresis
D)CsCl gradient ultracentrifugation
E)cryo-EM

Question 5

Which of these choices represents one possible corresponding mRNA sequence that can be transcribed from the following DNA template? 5′ - CTGTATCCTAGCACCCAAATCGCATTAGGAC - 3′

A)5′ - ATG CGA TTT GGG TGC TAG - 3′
B)5′ - AUG CGA UUU GGG UGC UAG - 3′
C)5′ - AUG CGA UUU GGG UGC - 3′
D)5′ - CTA GCA CCC AAA TCG CAT TAG - 3'
E)3′ - GGA CAU AGG UAC GUG GGU UUA GCG UAA UCC UG - 5′

Question 6

Which of the following are synonymous codons?

A)UUC and UUG
B)UCC and UAC
C)CGA and AGA
D)AGG and AGC
E)AAG and AAC

Question 7

A mutagen has introduced a frame-shift mutation by adding one nucleotide base.Which of the following would be classified as a reversion mutation for this particular mutant?

A)deleting 2 bases
B)adding 1 base
C)deleting 1 base or adding 1 base
D)deleting 1 base or adding 3 bases
E)deleting 1 base or adding 2 bases

Question 8

In the unlikely event that a tRNA has been charged with the wrong amino acid,what high-fidelity enzyme is likely to blame?

A)peptidyl transferase
B)DNA polymerase I
C)DNA polymerase III
D)aminoacyl synthetase
E)aminoacyl peptidase

Question 9

During translation initiation in prokaryotes,the amino acid on the initiator tRNA is

A)methionine (Met).
B)N-formylmethionine (fMet).
C)acetylated.
D)IF-1.
E)added using ATP as the energy source.

Question 10

The Shine-Dalgarno sequence

A)is a purine-rich consensus sequence found in the 5′ UTR of the mRNA.
B)is a pyrimidine-rich consensus sequence found in the 3′ UTR of the mRNA.
C)is a purine-rich consensus sequence found in the 16S rRNA subunit.
D)is a region of the tRNA molecule involved in formation of charged tRNAs.
E)is a consensus sequence involved in the termination of translation.

Question 11

What would you expect to find bound to the stop codon at the A site?

A)a charged tRNA with the anticodon TAG
B)a charged tRNA with the anticodon ATC
C)an uncharged tRNA
D)a release factor
E)Nothing binds to a stop codon,which is why the peptide is released.

Question 12

Which step in translation initiation is unique to eukaryotes?

A)formation of the preinitiation complex
B)formation of the initiation complex
C)scanning
D)ribosome assembly
E)translocation of the ribosome in the 3′ direction

Question 13

Which single-base mutation would insert a premature stop codon into the following protein sequence? N-Met-Gln-Leu-Arg-Cys-C

A)5′ - AUG CAG AUA GCG UGC UAG - 3′
B)5′ - AUG AAG UUA GCG UGC UAG - 3′
C)5′ - AUG CAG UAA GCG UGC UAG - 3′
D)5′ - AUG CAG UUA UUG UGC UAG - 3′
E)5′ - AUG CAG UUA GCG UGC AAG - 3′

Question 14

A polycistronic mRNA contains multiple what?

A)promoters
B)Shine-Dalgarno sequences
C)Kozak sequences
D)mRNAs
E)polypeptide-producing sequences

Question 15

Given the following mRNA sequence,what is the amino acid sequence for the corresponding polypeptide? 5′ - AUG CGA UUU GGG UGC UAG - 3′

A)5′-Met-Arg-Phe-Gly-Stop-3′
B)C-Met-Arg-Leu-Glu-N
C)N-Met-Arg-Phe-Gly-Cy-C
D)N-Met-Asp-Phe-Gly-Trp-C
E)N-Arg-Phe-Gly-Stop-C

Question 16

What result would you expect if you mutate one of the four arms of a tRNA?

A)The tRNA will fit into the A site but will not release the peptide at the P site.
B)The tRNA will not be recognized by tRNA synthetase and cannot be charged.
C)The tRNA will be charged with the wrong amino acid.
D)The tRNA will not be able to undergo traditional complementary base pairing.
E)There will be no effect on function,so long as the anticodon region is intact.

Question 17

How does the eukaryotic initiation complex locate the true start codon?

A)The true start codon is the first ATG encountered downstream of the Shine-Dalgarno sequence.
B)The initiation complex moves the small ribosomal subunit through the 5′ UTR,scanning for the start AUG.
C)The preinitiation complex moves the ribosome through the 3′ UTR,scanning for the Kozak sequence.
D)The true start codon is the first ATG encountered downstream of the Kozak sequence.
E)The true start codon is the formyl-ATG,which will encode for fMet in the protein.

Question 18

Experiments by Chapeville and colleagues proved that the genetic code derives its specificity through what interactions?

A)hydrogen bonds and disulfide bonds that maintain the shape of the tRNAs
B)complementary base pairing between amino acids and tRNA
C)complementary base pairing between tRNA and mRNA
D)ionic bonds between the small and large subunits of the ribosome
E)hydrogen bonding between the ribosomal subunits and the mRNA

Question 19

Given the following mRNA sequence,which of the following mutations would affect the protein sequence? 5′ - AUG CAG UUA GCG UGC UAG - 3′

A)5′ - AUG CAA UUA GCG UGC UAG - 3′
B)5′ - AUG CAG UUA GCA UGC UAG - 3′
C)5′ - AUG CAG UUG GCG UGC UAG - 3′
D)5′ - AUG CAA UUA GCG UGU UAG - 3′
E)5′ - AUG CAC UUA GCA UGC UAG - 3′

Question 20

You have identified a bacterial protein that has retained the starting fMet in its protein sequence.Which of the following is likely true of this protein?

A)It is likely nonfunctional,since bacteria use posttranslational cleavage of fMet to make functional proteins.
B)It will show improper protein sorting and will likely remain in the ER.
C)It will be not be able to be chemically modified,so it will be sent to the Golgi for secretion.
D)It will be a functional bacterial protein,since all functional proteins must begin with fMet.
E)It will likely form a disulfide bond with a second peptide chain,forming a protein complex.

Question 21

If you are designing an antibiotic that inhibits peptide bond formation,what protein would you target?

Question 22

The preinitiation complex forms when the start codon is recognized through binding of 16srRNA and what region of mRNA?

Question 23

Khorana used synthetic mRNAs to determine genetic code possibilities.To do so,he translated synthetic mRNA in vitro in the presence of individual ¹⁴C-labeled amino acids.What polypeptide did he identify using the repeating dinucleotide Poly-UG?

Question 24

In a polyribosome,which end of the mRNA would have the shortest polypeptides?

Question 25

Binding of what protein initiates translation-termination events that result in polypeptide release and dissociation of ribosomal subunits?

Question 26

What molecule provides the energy to form charged tRNAs?

Question 27

Ribosomal subunits are measured in which units,which describe the speed of sedimentation of a substance during centrifugation?

Question 28

What process is targeted by the antibiotic streptomycin?

Question 29

What reaction provides the energy for the eukaryotic ribosome to search for the start ATG during the process of scanning?

Question 30

What are the three phases of translation?

Question 31

Thanks to flexible base pairing,the wobble nucleotides in anticodons can be any of the RNA nucleotides or which modified nucleotide?

Question 32

Sidney Brenner proved that the triplet code is,in fact,nonoverlapping.Assuming a nonoverlapping code,how many complete codons would the following sequence encode before encountering a stop codon? 5′ - AUGCGAUUAUAGUGC - 3′

Question 33

During elongation,where does the charged tRNA is recruited to which location on the ribosome?

Question 34

If the pH gradient in a two-dimensional gel is lost,which step during two-dimensional electrophoresis would be affected?

Question 35

In the ER,misfolded proteins are identified and bound by what molecules?

Question 36

How many different aminoacyl-tRNA synthetases can be found in a given cell?

Question 37

In the Golgi,what type of protein modification will signal the polypeptide destination by determining the receptor to which the peptide will bind?

Question 38

Many antibiotics cause mispairing between codons and anticodons.What fatal effect would this mispairing have on the cell?

Question 39

Eighteen of the amino acids have two or more synonymous codons.Which two amino acids are the exceptions?

Question 40

Sidney Brenner designed an experiment to determine if the triplet code was overlapping or nonoverlapping.If the code were overlapping,how many complete codons would the following sequence encode before encountering a stop codon?
5′ - AUGCGAUUAUAGUGC - 3′

Question 41

Using mathematical reasoning,a triplet genetic code gives a possible ________ different codons,while a doublet genetic code would yield ________ different codons.Thus,the triplet code accounts for 20 known amino acids and indicates redundancy in the genetic code.

Question 42

Starting translation at the authentic (correct)start codon is essential for translation of the correct polypeptide.Errant translation starting at the wrong codon,or even at the wrong nucleotide of the start codon,may produce an abnormal polypeptide and result in a nonfunctional protein.Compare and contrast the mechanisms used by bacteria and eukaryotes to identify the authentic start codon during translation initiation.

Question 43

________ help control ribosome formation and binding of the initiator tRNA.

Question 44

In eukaryotes,the initiation factor proteins eIF1A and eIF3 join with ________ to form the preinitiation complex.

Question 45

Describe the process of two-dimensional gel electrophoresis.What are the two dimensions referring to? How is this technique different from conventional gel electrophoresis,and when would it be used?

Question 46

Prokaryotes and eukaryotes show differences in posttranscriptional modifications of mRNA.What are these differences,and why do eukaryotes show more modifications than prokaryotes?

Question 47

Compare and contrast the mechanism of action of two commonly used antibiotics.Include details about which steps of translation are inhibited,and explain how the antibiotic accomplishes this inhibition.

Question 48

A signal sequence at the N-terminus of newly synthesized proteins will direct the protein to the ________ for protein packaging.

Question 49

Describe what is meant by a "conformational disease" and give an example.Why do you think these diseases exhibit late age of onset?

Question 50

Bacteria group their genes such that they share a single promoter and the mRNA transcript synthesizes several different polypeptides.Collectively,these are referred to as ________ mRNAs,which are part of the operon system.

Question 51

Polypeptides must be sorted after translation.Does protein sorting occur in both prokaryotes and eukaryotes? Describe the process of protein sorting and explain how the signal sequence is involved.What would you expect to see if the signal sequence has been mutated or deleted?