Deck 9: The Molecular Biology of Translation

Question 1

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

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

Answer 1

E

Question 2

What is the cellular location of the stages of translation in bacteria and eukaryotes?

A) cytosol for bacteria and eukaryotes
B) membrane for bacteria and cytosol and rough ER for eukaryotes
C) cytosol for bacteria and cytosol, mitochondrion, and plastid for eukaryotes
D) nucleoid for bacteria and rough ER for eukaryotes
E) cytosol for bacteria and nucleus for eukaryotes

Answer 2

C

Question 3

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

A) The tRNA will not be recognized by tRNA synthetase and cannot be charged.
B) The tRNA will fit into the A site but will not release the peptide at the P site.
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.

Answer 3

A

Question 4

How does the eukaryotic ribosomal small subunit recognize the start codon on the mRNA?

A) It binds an Met- tRNA to the first AUG codon it encounters.
B) It binds an Met- tRNA to the first AUG codon after the Kozak sequence.
C) It performs an ATP hydrolysis within the small subunit once it encounters a Met- tRNA already bound to the AUG.
D) It undergoes a conformational charge that recruits other proteins when it hydrogens bonds to the correct tri- nucleotide sequence.
E) It wraps the mRNA strand to bring initiation enhancer proteins into the vicinity of the start codon.

Question 5

What is necessary for a eukaryotic RNA to be recognized and bound by the small subunit of the ribosome?

A) Sufficiently large 5' UTR for ribosome scanning.
B) Presence of an AUG start codon near the 5' end of the mRNA.
C) Formation of the pre- initiation complex before ribosome binding.
D) Presence of 5' methyl- G cap on the mRNA.
E) Formation of the initiation complex before ribosome binding.

Question 6

The Shine- Dalgarno sequence in bacteria .

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

Question 7

Why are eukaryotic mRNAs not polycistronic, unlike some bacterial transcripts?

A) The eukaryotic ribosome must bind to the 5' end of the mRNA and scan, while the bacterial ribosome can bind to a Shine- Delgarno sequence anywhere in the mRNA.
B) Bacteria couple their translation with transcription, while eukaryotes do not.
C) Eukaryote's genetic code is non- overlapping, and so coding sequences cannot overlap on the same mRNA.
D) Eukaryotes have more complex translational machinery than bacteria that is also less efficient in initiating translation.
E) Eukaryotic mRNAs are generally shorter than bacteria mRNAs, and so do not contain sufficient information to encode additional polypeptides.

Question 8

Identification of ribosomal proteins involves two- dimensional gel electrophoresis, which separates the proteins on the basis of _ .

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

Question 9

A portion of an mRNA attached to a ribosome reads: 5' GACCAUUUUUGA 3'
If a tRNA with a Phenylalanine amino acid attached is in the P site of the ribosome, an empty tRNA present in the E site that delivered which amino acid?

A) serine
B) proline
C) aspartic acid
D) tyrosine
E) histidine

Question 10

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

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

Question 11

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

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

Question 12

If a tRNA anticodon were mutated such that it no longer performed wobble, what would be the effect on encoded proteins?

A) A different amino acid would consistently replace the amino acid whose tRNA was mutated.
B) Many proteins would be truncated.
C) The rate of protein synthesis would be slowed.
D) Many proteins would have several mutated amino acids throughout their sequence.
E) The ribosome would be unable to translate proteins.

Question 13

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

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

Question 14

A tRNA in the P site of the ribosome will enter the site after translocation of the ribosome.

A) A
B) initiation
C) 3'
D) 5'
E) E

Question 15

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

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

Question 16

How many different aminoacyl- tRNA synthetases can be found in a given organism's cells?

A) At least 20, or more depending on the organism
B) 16
C) 61
D) 20
E) The number varies greatly depending on the organisms type.

Question 17

What features of proteins does two- dimensional gel electrophoresis exploit in order to separate proteins?

A) charge and pH
B) shape and size
C) pH and polarity
D) charge and shape
E) size and charge

Question 18

A polycistronic mRNA contains multiple .

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

Question 19

A portion of mRNA attached to a ribosome reads: 5' GACCAUUUUUGA 3'
In the polypeptide produced, what amino acid will be attached to the amino group of the histidine encoded by this mRNA?

A) aspartic acid
B) proline
C) tyrosine
D) phenylalanine
E) serine

Question 20

What does it mean for two codons to be synonymous?

A) They share one of the same nucleotides in their codon sequence.
B) They share two of the same nucleotides in their codon sequence.
C) They are adjacent on the mRNA.
D) They encode the same amino acid.
E) They occur in equal abundance in an mRNA sequence.

Question 21

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

Question 22

Given the following mRNA sequence, which of the following mRNAs would encode a protein with a different sequence of amino acids? 5' - AUG CAG UUA GCG UGC UAG - 3'

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

Question 23

Which of these choices represents one possible corresponding mRNA sequence that can be transcrib 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) 3' - GGA CAU AGG UAC GUG GGU UUA GCG UAA UCC UG - 5'
E) 5' - CTA GCA CCC AAA TCG CAT TAG - 3'

Question 24

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

Question 25

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

Question 26

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

Question 27

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

Question 28

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

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

Question 29

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

Question 30

What molecule provides the energy to form charged tRNAs?

Question 31

If the genetic code were overlapping, how many complete codons would the following sequence encode before encountering a stop codon? 5' - AUGCGAUUAAAGUGC - 3'

A) 10
B) 13
C) 8
D) 6
E) 4

Question 32

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

Question 33

Which mRNA below would code for a premature stop codon from the following amino acid sequence? N-Met- Gln- Leu- Arg- Cys-C

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

Question 34

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

Question 35

How is a tRNA able to recognize its proper mRNA codon?

A) Hydrogen bonding between the ribosomal subunits and the mRNA creates the proper active site conformation to allow tRNA binding.
B) Complementary hydrogen bonding between tRNA and mRNA promote binding.
C) The amino acid on the tRNA recognizes the mRNA codon through hydrogen and ionic bonding.
D) Ionic bonds between the tRNA and the active site of the ribosomal subunits promote binding to the mRNA.
E) Appropriate shape of the tRNA allows it to fit onto the extended mRNA strand.

Question 36

If the first nucleotide in a codon is mutated to a different nucleotide, what would be the effect on the encoded protein?

A) A missense mutation from one encoded amino acid changing to another.
B) It depends on what the changed nucleotide is.
C) A frameshift mutation for all of the subsequent amino acids in the protein.
D) No effect as the problem nucleotide would be corrected by RNA editing mechanisms.
E) A silent mutation and no change in the encoded amino acid.

Question 37

What are the three phases of translation?

Question 38

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

Question 39

In the unlikely event that a tRNA has been charged with the wrong amino acid, which high- fidelity enzyme most likely caused the incorrect charging?

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

Question 40

How might a single base INSERTION into the second codon of the coding sequence of a gene affect the amino acid sequence of a protein encoded by the gene?

A) A single amino acid could change.
B) The mutation may have no effect on amino acid sequence.
C) The amino acid sequence would be changed.
D) A single extra amino acid would be present in the protein.
E) All of the above are possible outcomes.

Question 41

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

Question 42

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 43

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

Question 44

Sidney Brenner demonstrated 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 45

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 46

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

Question 47

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?

Question 48

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

Question 49

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

Question 50

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

Question 51

Describe the technique 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 52

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 53

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 54

help control ribosome formation and binding of the initiator tRNA.

Question 55

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