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

Accepted Answer

Proteins become embedded in the ER membrane through stop- and start-transfer sequences that direct the insertion and orientation of the polypeptide into the membrane, creating transmembrane proteins.

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.

Accepted Answer

EF-Tu is involved in the elongation phase of prokaryotic translation by facilitating the entry of aminoacyl tRNA into the ribosome.

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

Accepted Answer

The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER). It slows the production of most proteins to reduce the load of unfolded proteins that need to be processed, while simultaneously increasing the production of proteins required for protein folding and degradation to help manage and clear the backlog of unfolded or misfolded proteins.

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.

Accepted Answer

The 3ʹ poly(A) tail and Poly(A) Binding Protein (PABP) interact with the initiation factor eIF4G, which helps to stabilize the 5ʹ cap structure of the mRNA. This interaction is crucial for the initiation of translation in eukaryotes, as it facilitates the recruitment of the ribosome to the mRNA.

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.

Accepted Answer

Peptidyl transferase is an enzymatic activity of the ribosome, specifically associated with the large subunit, that catalyzes the formation of peptide bonds between amino acids during protein synthesis. It functions as a ribozyme, meaning its catalytic activity is not protein-based but rather RNA-based. It does not require ATP or any external energy source to catalyze peptide bond formation. However, peptidyl transferase itself does not move the ribosome along the mRNA; this movement is facilitated by other factors involved in translation.

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.

Accepted Answer

In eukaryotes (eukarya), most mRNAs are monocistronic, meaning they typically carry the information for just one protein. In contrast, prokaryotes (bacteria and archaea) often have polycistronic mRNAs, which contain the information for multiple proteins.

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.

Accepted Answer

A mutation in the Shine-Dalgarno sequence of the DNA would result in mRNA that binds poorly to the ribosome, explaining the difficulty in obtaining protein from the mRNA in an in vitro translation system.

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

Accepted Answer

Polyadenylation, the addition of a poly(A) tail to RNA, is a process associated with RNA processing, not post-translational processing of proteins.

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.

Accepted Answer

To ensure a protein accumulates within the ER of yeast cells, it's essential to incorporate the appropriate DNA sequences that will create signal sequences in the mature peptide. These signal sequences direct the protein to the ER during its synthesis.

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

Accepted Answer

Aminoacylation of tRNA does not involve the hydrolysis of GTP; it involves the attachment of an amino acid to its corresponding tRNA molecule, a process that uses ATP as the energy source, not GTP.

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

Accepted Answer

Lysosomes receive proteins through a pathway that involves synthesis in the rough endoplasmic reticulum (ER) and sorting in the Golgi apparatus, not by direct posttranslational import from the cytoplasm.

Question 12

Release factors of translation recognize the codon
A)AUG.
B)GUA.
C)UGA.
D)GGA.
E)UUU.

Accepted Answer

Release factors of translation recognize stop codons, not start or coding codons. AUG is a start codon, while UGA is one of the three stop codons (along with UAA and UAG) that signal the end of protein synthesis.

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.

Accepted Answer

Cells that incorporate selenocysteine and pyrrolysine into their proteins require two additional tRNAs and two additional aminoacyl-tRNA synthetases to recognize and attach these unique amino acids to their respective tRNAs.

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)

Accepted Answer

The Kozak sequence is a specific sequence around the start codon (AUG) in eukaryotic mRNA that plays a major role in the initiation of the translation process. The consensus sequence, which includes ACCAUGG, helps the ribosome identify the start codon and initiate protein synthesis efficiently.

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

Accepted Answer

The small ribosomal subunit binds to the mRNA before the large ribosomal subunit does, in both eukaryotes and prokaryotes, initiating the process of translation.

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.

Accepted Answer

Ribosomes that are not attached to the rough endoplasmic reticulum (ER) are typically found in the cytoplasm, synthesizing proteins that function within the cytosol rather than those destined for secretion or for the membrane. The other options (B, C, D) suggest defects that are not typically associated with the localization of ribosomes to the cytoplasm versus the ER.

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

Accepted Answer

Peptidyl transferase is the enzyme responsible for catalyzing the formation of peptide bonds between amino acids during the process of protein synthesis on the ribosome.

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

Accepted Answer

The genetic code is degenerate, meaning that most amino acids are encoded by more than one codon. Codons that encode the same amino acid typically differ only in the third nucleotide. UUC also encodes for phenylalanine, just like UUU.

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.

Accepted Answer

The large subunit of the eukaryotic ribosome contains 28S, 5.8S, and 5S rRNA molecules. The 16S rRNA is associated with the small subunit of prokaryotic ribosomes, not eukaryotic ones.

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.

Accepted Answer

All of these approaches are valid for examining how a colony has regained the ability to produce malate dehydrogenase despite the original mutation. A reversion could restore the original gene function (A), a suppressor mutation elsewhere could bypass the stop codon effect (B), a suppressor tRNA could allow read-through of stop codons (C), and the acquisition of a new copy of the gene could compensate for the mutated one (D).

Quiz 19: Gene Expression: Iiprotein Synthesis and Sorting

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

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

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

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

In which of the following groups are most mRNAs monocistronic?

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

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

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

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

Release factors of translation recognize the codon

Cells that use the amino acids selenocysteine and pyrrolysine have

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

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

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

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

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

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

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