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

Accepted Answer

Frameshift mutations disrupt the normal reading frame of the genetic code and can lead to premature termination of translation. Suppressor mutations can restore the reading frame and allow for translation of the full-length protein. In order to do this, suppressor tRNAs must recognize a codon that would normally signal a stop signal and insert an amino acid instead, or recognize a codon that is shifted by four or two nucleotides and insert the correct amino acid accordingly. Therefore, options B and C are both possibilities for suppressor tRNA anticodons that could restore the reading frame, and the correct answer is D. Option A is not correct, as suppressor tRNAs would recognize stop codons and insert an amino acid, rather than encoding one themselves.

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

Accepted Answer

Peptidyl transferase is the enzyme responsible for forming peptide bonds during protein synthesis. Peptidase, peptide hydrolase, and aminoacyl transferase are involved in other aspects of protein metabolism, while inteins are sequences within proteins that are removed through protein splicing but are not directly involved in peptide bond formation.

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

Accepted Answer

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

Accepted Answer

A comprehensive approach is needed to determine the mechanism by which the colony regained the ability to produce malate dehydrogenase. This includes checking for reversion mutations, suppressor mutations, suppressor tRNA activity, and the presence of additional gene copies.

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.

Accepted Answer

Chronic misfolding of a newly translated protein can be prevented by proper chaperone activity, which helps in the folding and stabilization of the protein. Defects in chaperone activity can result in misfolded proteins, leading to diseases such as prion diseases. Other options like foldase, insertion of proper amino acids, proteosome function, and translocase are also important in protein folding, but they are not primarily responsible for misfolding leading to disease.

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

Accepted Answer

Ribosomes are composed of two subunits, the small subunit (30S in bacteria) and the large subunit (50S in bacteria). The 16S rRNA gene is found in the small subunit of the ribosome and is highly conserved among different bacterial species. Likewise, the 18S rRNA gene is found in the small subunit of eukaryotic ribosomes and is highly conserved among different eukaryotic species. Therefore, molecular taxonomists use these rRNA sequences (16S and 18S) to determine the phylogenetic relationships between organisms. As ribosomes are found in all organisms (except viruses), these sequences can be used to analyze relationships across a wide range of taxa. Thus, the best choice is D, both choices A and B.

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

Accepted Answer

Pyrrolysine is not one of the 20 common amino acids found in cells. While it is an amino acid, it is rare and only found in some bacteria and archaea.

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.

Accepted Answer

Peptidyl transferase is not responsible for moving the ribosome during translation. This function is carried out by other proteins called elongation factors.

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

Accepted Answer

The answer of Which of the following steps in prokaryotic...

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

Accepted Answer

The different messages have sequences with more or less homology to the Shine-Dalgarno sequence. This sequence is recognized by the ribosome and allows for binding and initiation of translation. If the Shine-Dalgarno sequence is less homologous, fewer ribosomes will bind and result in less protein production. This explains why the quantities of each protein can vary in polycistronic messages. Feedback regulation (B) and coupling of transcription and translation (C) are not directly related to the graded production of proteins in polycistronic messages. There is typically a termination sequence at the end of each gene (D) which allows for separate translation of each protein.

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.

Accepted Answer

Signal sequences are short stretches of amino acids that direct the protein to the ER, where it can be retained or further processed.

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)

Accepted Answer

The sequence ACCAUGG is known as the Kozak sequence, named after its discoverer Marilyn Kozak. It is important in eukaryotic initiation as it directs the ribosome to the correct start codon for translation initiation.

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

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 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

Accepted Answer

EF-Tu is responsible for placing aminoacyl tRNAs onto the ribosome during elongation, making it the most likely site of action for an antibiotic that interferes with this process. IF3 is involved in the initiation of translation, while EF-Ts is involved in the regeneration of EF-Tu, and neither of these factors play a direct role in elongation.

Question 15

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

Accepted Answer

UGA is recognized as a stop codon by the release factors in translation. The other codons listed code for specific amino acids and are recognized by tRNA.

Question 16

Which of the following is not a prion disease?
A)scrapie
B)tuberculosis
C)mad cow disease
D)Creutzfeldt-Jacob disease

Accepted Answer

Tuberculosis is caused by a bacterial infection, not by prions. Scrapie is a prion disease that affects sheep and goats, mad cow disease is a prion disease that affects cows, and Creutzfeldt-Jacob disease is a prion disease that affects humans.

Question 17

Which of the following codons is associated with the amino acid phenylalanine?
A)AAA
B)UAG
C)AUG
D)AAC
E)UUU

Accepted Answer

The codon UUU is associated with the amino acid phenylalanine. This information can be found in a codon chart or table.

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

Accepted Answer

Lysosomes receive proteins through the secretory pathway, not by posttranslational import from cytoplasmic ribosomes.

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.

Accepted Answer

The slow growth and difficulty in obtaining protein in both in vivo and in vitro systems suggest that there is a problem with translation. The Shine-Dalgarno sequence of the mRNA is important for initiating translation by binding to the ribosome, so a mutation in this sequence could result in poor binding and inefficient translation. Therefore, option A is the best answer.

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.

Accepted Answer

16S rRNA is associated with the small subunit of the prokaryotic ribosome, but not with the large subunit of the eukaryotic ribosome.

Quiz 22: Gene Expression: Iiprotein Synthesis and Sorting

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.)

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

Which of the following organisms utilizes polycistronic mRNAs?

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

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) ?

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

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

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

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

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

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

Release factors of translation recognize the codon

Which of the following is not a prion disease?

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

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

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