Deck 22: Gene Expression: Iiprotein Synthesis and Sorting

Question 1

In studying an E.coli strain containing a known frameshift mutation,you isolate a mutant in which this frameshift is suppressed.You therefore expect to find which of the following associated with the suppression? (Assume the frameshift has not been corrected in the coding for the peptide.)

A)suppressor tRNAs encode an amino acid for a stop signal
B)suppressor tRNAs encode a four-nucleotide anticodon
C)suppressor tRNAs encode a two-nucleotide anticodon
D)both choices B and C
E)all of the above

Answer 1

D

Question 2

Which of the following enzymes is associated with the formation of peptide binds?

A)peptidase
B)aminoacyl transferase
C)peptidyl transferase
D)peptide hydrolase
E)inteins

Answer 2

C

Question 3

Which of the following organisms utilizes polycistronic mRNAs?

A)E. coli
B)C. elegans
C)mammals
D)choices A and B only
E)all of the above

Answer 3

E

Question 4

In a mutant E.coli strain,there was a mutation in the malate dehydrogenase gene that resulted in a stop codon at amino acid position 14.From subcultures of this strain,a colony was obtained that was capable of making malate dehydrogenase.Your approach to examining this phenomenon should be to examine

A)the DNA sequence to see if a reversion has occurred.
B)the DNA sequence to see if a suppresor mutation has occurred.
C)other proteins to see if other stop codons are ignored, indicating the presence of a suppresor tRNA.
D)the DNA and plasmids for the incorporation of a second complete copy of the malate dehydrogenase gene.
E)all of the above

Question 5

The appropriate folding of a newly translated protein is essential,and chronic misfolding often leads to disease,especially in vertebrates.This misfolding,particularly in the case of prion diseases,may be due to a defect in

A)the enzyme foldase.
B)insertion of proper amino acids during translation.
C)proteosome function.
D)chaperone activity.
E)translocase.

Question 6

Ribosomes are very old structures,found in all organisms (except viruses),from bacteria to humans.As a result,molecular taxonomists are looking at relationships based upon which rRNA sequence(s)?

A)16S
B)18S
C)30S
D)both choices A and B
E)all of the above

Question 7

Which of the following amino acids is not one of the 20 common amino acids found in cells?

A)leucine
B)isoleucine
C)glutamine
D)proline
E)pyrrolysine

Question 8

Which of the following statements is not true concerning peptidyl transferase?

A)It is a ribozyme having catalytic activity.
B)It catalyzes peptide bond formation.
C)It moves the ribosome, so translation continues.
D)It is associated with the large subunit of ribosomes.
E)It requires no outside source of additional energy, such as ATP.

Question 9

Which of the following steps in prokaryotic translation takes place first?

A)aminoacylation of the tRNA molecule
B)joining of 30S and 50S ribosomal subunits into 70S ribsomes
C)binding of mRNA to a ribosome
D)attachment of fMet aminoacyl tRNA
E)catalysis by RNA polymerase

Question 10

With regard to translation in prokaryotes,the gene products are often encoded on polycistronic mRNAs.As a result,the quantities of each of the proteins are often graded,such that the first gene has a great deal of protein translated,whereas the last gene has very little.Which of the following features of prokaryotic translation may account for increased production of some products and decreased production of others?

A)The different messages have sequences with more or less homology to the ShineDelgarno sequence; fewer ribosomes binding results in less product.
B)Feedback regulation of ribosomes tells the cell that enough product is made, and ribosomes from such mRNAs dissociate.
C)Because transcription and translation in prokaryotes are essentially coupled, there is no gradation in the amount of individual proteins made from a polycistronic message.
D)There is no termination sequence at the end of each gene, so one long protein is made, resulting in equal amounts of products.
E)all of the above

Question 11

Using the techniques of genetic engineering,you design a cytoplasmic protein you want to accumulate within the ER of yeast cells.To accomplish this goal,you need to

A)do nothing; all proteins go through the ER.
B)incorporate appropriate mannose-6-phosphate groups.
C)incorporate the appropriate DNA sequence(s)to create signal sequences into mature peptide.
D)incorporate radioactive amino acids into the protein.
E)incorporate the appropriate DNA sequence(s)to create signal sequences into the mature peptide.

Question 12

In eukaryotic initiation,one will often see the sequence ACCAUGG as a translational start sequence. This sequence is known as the ________ sequence.

A)Okazaki
B)ETS (eukaryotic translational start)
C)Kozak
D)IRES (internal ribosome entry sequence)
E)CIBS (complex initiation binding sequence)

Question 13

Of the following steps associated with translation,which does not involve hydrolysis of GTP?

A)aminoacylation of tRNA
B)formation of the initiation complex
C)binding of the aminoacyl tRNA to the codon at the A site
D)translocation of the ribosome
E)release of polypeptide

Question 14

In working with a potentially new antibiotic,you are attempting to determine where in prokaryotic translation this antibiotic has its effect.You have determined thus far that it interacts with a translational factor but need to identify which one.If this antibiotic interfered with elongation,which of the following factors could be a potential site of action?

A)IF3 interaction with an aminoacyl tRNA
B)EF-Tu placement of N-formylmethionine onto the ribosome
C)EF-Tu interaction with an aminoacyl tRNA
D)EF-Ts translocation of tRNAs from the A site to the P site
E)all of the above

Question 15

Release factors of translation recognize the codon

A)AUG.
B)GUA.
C)UGA.
D)GGA.
E)UUU.

Question 16

Which of the following is not a prion disease?

A)scrapie
B)tuberculosis
C)mad cow disease
D)Creutzfeldt-Jacob disease

Question 17

Which of the following codons is associated with the amino acid phenylalanine?

A)AAA
B)UAG
C)AUG
D)AAC
E)UUU

Question 18

Which of the following organelles does not receive proteins synthesized on cytoplasmic ribosomes by posttranslational import?

A)lysosome
B)nucleus
C)mitochondria
D)peroxisomes
E)chloroplast

Question 19

A mutant bacterium is isolated.This bacterial strain has the characteristic of very slow,"sickly" growth.You isolate mRNA from this bacteria to use in an in vitro translation system and note that even in vitro it is difficult to use this message and obtain protein.Of the following,which is a likely explanation for these results?

A)There may be a mutation in the ShineDelgarno sequence of the DNA, resulting in a RNA that poorly binds the ribosome.
B)There may be a mutation in the ribosomal rRNA recognizing the ShineDelgarno sequence of the message.
C)This mutant may have altered tRNA molecules, such that the codon-anticodon interaction during translation is affected.
D)These bacteria may not manufacture enough translation factors for effective translation.
E)In this mutant, the ribosomal subunits may not associate well enough for effective translation.

Question 20

Which of the following rRNA molecules is not associated with the large subunit of the eukaryotic ribosome?

A)28S
B)5.8S
C)5S
D)16S
E)Neither B nor D is associated.

Question 21

Which of the following nucleotides in the anticodon can allow for "wobble" in translation?

A)uracil
B)thymine
C)guanine
D)inosine
E)carboxycytosine

Question 22

Messenger RNAs containing premature stop codons are destroyed by the mechanism of

A)nonstop decay.
B)directed RNase activity.
C)nonsense-mediated decay.
D)error-mediated repair.
E)none of the above

Question 23

The initial amino acid incorporated into a nascent peptide is N-formylated in

A)eukaryotic translation.
B)prokaryotic transcription.
C)prokaryotic translation.
D)both choices A and C
E)both choices B and C

Question 24

The process by which cytosolic polypeptides are transported to a target organelle is via which of the following?

A)transportin mechanisms
B)posttranslational import
C)cotranslational import
D)the importin protein
E)the activity of ribosomes

Question 25

Which of the following requires eIFs for initiation?

A)E. coli translation
B)chaperonin activity
C)eukaryotic translation
D)eukaryotic transcription
E)DNA replication

Question 26

When one portion of a chromosome becomes physically part of another chromosome,the type of mutation is referred to as a(n)

A)nonsense mutation.
B)inversion.
C)translocation.
D)duplication.
E)nonstop mutation.

Question 27

Intramolecular protein splicing results in the formation of the final protein and the

A)protease.
B)proteosome.
C)inteins.
D)all of the above
E)none of the above

Question 28

Segments of polypeptides that are retained following protein splicing are called

A)introns.
B)exons.
C)inteins.
D)exteins.
E)cleaved.

Question 29

In the following gene sequence,the original sequence is ABC* DEFGH. It now reads ABC* DGFEH.The * indicates the centromere. This type of mutation is a(n)

A)nonsense mutation.
B)inversion.
C)translocation.
D)duplication.
E)point mutation.

Question 30

Which of the following activities is not associated with posttranslational processing?

A)glycosylation
B)specific cleavage of polypeptides
C)chaperonin activity
D)addition of lipid groups
E)polyadenylation

Question 31

Messenger RNAs that contain no stop codons due to a frameshift mutation are eliminated by

A)nonstop decay.
B)directed RNase activity.
C)nonsense-mediated decay.
D)error-mediated repair.
E)none of the above

Question 32

If more than one codon specifies the same amino acid,the code is said to be

A)complementary.
B)inverse.
C)redundant.
D)ambiguous.
E)degenerate.

Question 33

AUG is the "start" codon in

A)prokaryotic translation.
B)eukaryotic translation.
C)both prokaryotic and eukaryotic translation.
D)neither prokaryotic nor eukaryotic translation.
E)prokaryotic modification.

Question 34

Peptide bond formation is catalyzed by an RNA molecule in

A)prokaryotes.
B)eukaryotes.
C)yeast only.
D)cyanobacteria.
E)both choices A and B

Question 35

Shine-Delgarno sequences are present in mRNAs of

A)prokaryotes.
B)eukaryotes.
C)fungi.
D)algae.
E)mosses.

Question 36

Ribosomes that do not anchor on the surface of the rough endoplasmic reticulum during translation most probably

A)are synthesizing cytoplasmic proteins.
B)have a defect in ribosomal proteins that allow attachment to the surface.
C)have a signal peptidase error.
D)do not make the appropriate anchor protein.
E)all of the above

Question 37

Of the following codons,which encodes a normal translational stop?

A)UUU
B)AUG
C)UAG
D)AAA
E)AGG

Question 38

The mRNA is translated in the 3' to 5' direction in

A)prokaryotes.
B)eukaryotes.
C)archaea.
D)all of the above
E)none of the above

Question 39

All of the following are associated with a protein-folding disease except

A)prions.
B)tau protein.
C)amyloid plaques.
D)E-cadherin.
E)apoplipoprotein E.

Question 40

Polycistronic mRNAs encode

A)one product that it alternatively spliced.
B)more than one protein.
C)a single message.
D)exclusively archaeal proteins.
E)none of the above

Question 41

The ________ (enzymes)link amino acids with their appropriate tRNAs.

Question 42

Typically,the first amino acid incorporated in bacterial protein synthesis is ________.

Question 43

Within the endoplasmic reticulum,________ recognizes misfolded or unassembled proteins and transports them back to the cytosol.

Question 44

The anticodon base ________ is able to bind U,C,or A,allowing for wobble in the anticodon region during translation.

Question 45

The ________ allows for flexibility in the codon:anticodon interaction at the third position.

Question 46

Once an amino acid has been attached to the appropriate tRNA,the tRNA is called a(n)________,and the amino acid is said to be ________.

Question 47

The sequence of amino acids in a protein is based on the ________ of the mRNA.

Question 48

Design an experiment whereby you could determine that the genetic code of a novel organism is based on a four-nucleotide codon.

Question 49

________ degrades mRNAs that contain premature stops.

Question 50

________ is a rare,intramolecular posttranslational process that allows for self-catalytic removal of specific amino acid sequences.

Question 51

________ degrades mRNAs that contain no stop codons.

Question 52

The transfer of polypeptides into the ER is called ________ because the movement across the membrane is coupled with translation.

Question 53

The newly arriving tRNA binds in the region of the ribosome known as the ________ site.

Question 54

In bacteria,a unique RNA that binds the A site of the ribosome and directs the addition of approximately 12 amino acids to the nascent peptide when no stop codon is present is called the ________.

Question 55

In cloning a gene,you discover that the gene product is much longer than should be observed based upon the insert you successfully cloned.What problems would result in a longer cloned sequence? How will you go about investigating your hypothesis? Would your answer change based upon the presence or absence of introns? Why or why not?

Question 56

You want to clone a eukaryotic gene and express the protein in yeast.However,the protein typically localizes within mitochondria.How will you perform your gene cloning so that the protein is secreted from the cell,rather than localized within yeast mitochondria?

Question 57

Discuss some of the possible ways in which nonsense mutations can potentially be suppressed in a cell.

Question 58

In bacteria,it is common to produce polycistronic messages,while in eukaryotes it is less common.Describe how polycistronic mRNAs are made and processed in prokaryotes and eukaryotes.How might polycistronic mRNA molecules be an advantage for eukaryotes?