Deck 19: Gene Expression: Iiprotein Synthesis and Sorting

Question 1

How do proteins become embedded in the membrane of the endoplasmic reticulum?

A)by protein chaperones that insert polypeptides into the ER membrane
B)by splicing of proteins on either side of the ER membrane
C)via stop- and start-transfer sequences that stop and start translocation of a polypeptide through the ER membrane,resulting in transmembrane proteins
D)by post-translational import can results in a transmembrane ER protein
E)via transit sequences that target polypeptides made in the cytosol for the ER membrane

Answer 1

C

Question 2

You are attempting to determine which step of prokaryotic translation a new antibiotic inhibits.You have determined that the antibiotic interacts with a translational factor but need to identify which one.If the new antibiotic interferes 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 these could be potential sites of action.

Answer 2

C

Question 3

The unfolded protein response slows the production of ________ and increases the ________.

A)signal recognition particles; activity of proteasomes
B)most proteins; production of lysosomal proteins
C)protein disulfide isomerase; activity of proteasomes
D)most proteins; production of proteins required for protein folding and degradation

Answer 3

D

Question 4

In eukaryotes,the 3ʹ end of the mRNA is important in the initiation of translation because

A)it contains Kozak sequences that aid in initiation.
B)translation occurs in the 3ʹ to 5ʹ direction.
C)eIF4A is attached to the 3ʹ end and removes any secondary structure that might prevent translation.
D)the 3ʹ poly(A)tail and PABP bind initiation factor eIF4G,stabilizing the 5ʹ end of the mRNA.
E)it contains Kozak sequences that aid in initiation of translation in the 3ʹ to 5ʹ direction.

Question 5

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 6

In which of the following groups are most mRNAs monocistronic?

A)bacteria
B)archaea
C)eukarya
D)bacteria and archaea
E)All mRNAs are monocistronic.

Question 7

A strain of mutant bacteria has been isolated.You isolate the mRNA corresponding to the mutated gene from this bacterial strain 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 Shine-Dalgarno sequence of the DNA,resulting in mRNA that binds poorly to the ribosome.
B)There may be a mutation in the ribosomal rRNA recognizing the Shine-Dalgarno sequence of the message.
C)This mutant may have altered tRNA molecules,such that the codon-anticodon interaction during translation is affected.
D)This mutant 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 8

Which of the following activities is not associated with post-translational processing?

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

Question 9

Using the techniques of genetic engineering,you design a 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 in the mature peptide.
D)incorporate radioactive amino acids into the protein.
E)remove the N-formyl group located at the N-terminus of the polypeptide.

Question 10

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 11

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

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

Question 12

Release factors of translation recognize the codon

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

Question 13

Cells that use the amino acids selenocysteine and pyrrolysine have

A)two more codons compared to other cells.
B)two more tRNAs compared to other cells.
C)two more aminoacyl-tRNA synthetases compared to other cells.
D)two more tRNAs and aminoacyl-tRNA syntheses compared to other cells.
E)inosine at the third position of their tRNA anticodons to accommodate these amino acids.

Question 14

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 15

During initiation of translation in both eukaryotes and prokaryotes the ________ binds before the ________.

A)large ribosomal subunit; small ribosomal subunit
B)small ribosomal subunit; large ribosomal subunit
C)EF-Tu; tRNA
D)EF-G; EF-Tu
E)ribosomes; initiation factors

Question 16

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 are probable reasons.

Question 17

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

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

Question 18

The codon for phenylalanine is UUU.Which of the following codons also most likely encodes for phenylalanine?

A)AAA
B)CUU
C)AUG
D)AUU
E)UUC

Question 19

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 5.8S nor 5S rRNA is associated with the large subunit.

Question 20

An E.coli strain contains a mutation in the malate dehydrogenase gene that results 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 suppressor mutation has occurred.
C)other proteins to see if other stop codons are ignored,indicating the presence of a suppressor tRNA.
D)the DNA and plasmids for the incorporation of a second complete copy of the malate dehydrogenase gene.
E)All of these approaches need to be considered.

Question 21

Cytosolic polypeptides are transported to a target organelle via

A)transportin mechanisms.
B)post-translational import.
C)cotranslational import.
D)the importin protein.
E)the activity of ribosomes.

Question 22

Inosine is found

A)in aminoacyl-tRNA synthetases.
B)in some eukaryotic elongation factors.
C)in rRNA.
D)in the third position of some codons.
E)in the third position of some anticodons.

Question 23

The normal sequence of genes along a hypothetical chromosome is ABC*DEFGH,where letters represent genes and the asterisk (*)represents the centromere.A mutation event results in a chromosome in which the sequence of genes is ABC*DGFEH.This type of mutation is

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

Question 24

Which of the following requires eIFs for initiation?

A)prokaryotic translation
B)chaperonin activity
C)eukaryotic translation
D)eukaryotic transcription
E)post-translational modification

Question 25

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

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

Question 26

The transfer of polypeptides into the ER is called

A)transit sequence import.
B)post-translational import.
C)cotranslational import.
D)endoplasmic import.
E)ribosomal import.

Question 27

Peptide bond formation is catalyzed by an RNA molecule in

A)prokaryotes.
B)eukaryotes.
C)viruses.
D)archaea.
E)both prokaryotes and eukaryotes.

Question 28

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 29

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

A)bacteria.
B)eukaryotes.
C)archaea.
D)eukaryotes,bacteria,and archaea.
E)None of these.

Question 30

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 31

Messenger RNAs that contain no stop codons are eliminated by

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

Question 32

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

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

Question 33

The presence of a transit sequence directs a protein from the ________ to the ________.

A)cytosol; mitochondrion or chloroplast
B)endoplasmic reticulum; Golgi apparatus
C)cytosol; plasma membrane
D)endoplasmic reticulum; nucleus
E)signal recognition particle; nucleus

Question 34

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

A)protease.
B)proteasome.
C)inteins.
D)exteins.
E)None of these.

Question 35

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

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

Question 36

Segments of polypeptides that are retained following protein splicing are called

A)introns.
B)exons.
C)inteins.
D)exteins.
E)cleavage products.

Question 37

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 these mechanisms.

Question 38

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

A)cytosine
B)thymine
C)adenine
D)inosine
E)carboxycytosine

Question 39

Polycistronic mRNAs encode

A)one product that is alternatively spliced.
B)more than one protein.
C)multiple cis elements.
D)exclusively eukaryotic proteins.
E)None of these.

Question 40

Shine-Dalgarno sequences are present in mRNAs of

A)prokaryotes.
B)eukaryotes.
C)humans.
D)plants.
E)both prokaryotes and eukaryotes.

Question 41

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 42

________ degrades mRNAs that contain premature stops.

Question 43

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

Question 44

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

Question 45

During elongation,each newly arriving tRNA binds in the region of the ribosome known as the ________ site.

Question 46

You discover a pattern of a 20 amino acid sequence at the C-terminus of over 50 proteins in an organism.You hypothesize that this amino acid sequence is a signal sequence for localization into a specific organelle or cell compartment,but you don't know which one.How might you use microscopy to investigate the location of proteins with this unique C-terminus sequence?

Question 47

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

Question 48

________ is an intramolecular post-translational process that allows for self-catalytic removal of specific amino acid sequences.

Question 49

The ________ are enzymes that link amino acids with their appropriate tRNAs.

Question 50

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

Question 51

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

Question 52

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

Question 53

You want to clone a eukaryotic gene and express the corresponding 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 54

You have cloned a eukaryotic gene,and inserted it into a bacterial system for expression.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 55

The first amino acid incorporated in bacterial protein synthesis is ________.

Question 56

In bacteria,it is common to produce polycistronic messages; 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?

Question 57

________ degrades mRNAs that contain no stop codons.