Unit 4 Quizzes Molecular Bio

The “adaptor” molecule that was hypothesized by Francis Crick to link amino acids to mRNA is actually which type of biomolecule?

a. a protein  

b. DNA 

c.tRNA 

d. rRNA 

c.tRNA 

What is the sequence of the last three nucleotides of all mature tRNA molecules?

1. tRNA molecules are single-stranded RNAs. 

2.   The 3'-terminal nucleotide of tRNA is the site of amino acid attachment. 

3.   The anticodon arm of tRNA contains a three nucleotide sequence that is identical to a specific mRNA codon. 

4.   tRNA molecules contain the unusual nucleotides dihydrouridine, pseudouridine, and ribothymine.

c. The anticodon arm of tRNA contains a three nucleotide sequence that is identical to a specific mRNA codon. 

Which one of the following describes a tRNA molecule that specifically recognizes the codon for the amino acid histidine, but is covalently bound (charged with) to the amino acid serine?

a. histinyl-tRNASer

b. histinyl-tRNAHis

c. seryl-tRNASer

d. seryl-tRNAHis

d. seryl-tRNAHis

5. The two codons for glutamine are CAA and CAG. Which one of the following is likely to be the anticodon of a tRNA that is specific for glutamine?

a. GUC 

1.   CGU 

2.   CUG 

3.   GCU

CUG

6. What is the approximate minimum length of an mRNA molecule that encodes a protein with a molecular weight of 30,000 Da? (The average molecular weight of an amino acid is 110 Da)

1. 275 nucleotides 

2.   550 nucleotides 

3.   825 nucleotides 

4.   2,475 nucleotides

c. 825

7. How many codons of the genetic code are used for coding amino acids?

1. 61 

2.   64 

3.   20 

4.   128

61

8. Which one of the following nucleotides does not form a wobble pair with inosine?

1. C 

2.   G 

3.   U 

4.   A

G

Which of the following RNAs use a Ran-independent pathway for the transport of RNA across the nuclear membrane?

1. mRNA 

2.   tRNA 

3.   rRNA 

4.   snRNA

mRNA

10. Which of the following nuclear RNA transport events requires the action of a guanine exchange factor (GEF)?

1. importin release of RNA in the nucleus 

2.   exportin release of RNA in the cytoplasm 

3.   importin binding of RNA in the cytoplasm 

4.   exportin binding of RNA in the nucleus

1. importin release of RNA in the nucleus 

11. Which proteins are bound at the exon-exon borders and facilitate transport of the spliced mRNA from the nucleus to the cytoplasm?

1. exportins 

2.   karyopherins 

3.   MAGOH and eIF4AIII 

4.   Ran-GTP complex

1.   MAGOH and eIF4AIII 

1. Name the type of chemical bonds that link a codon in mRNA to an anticodon in tRNA:

1. phosphodiester 

2.   hydrogen 

3.   amide 

4.   ether

hydrogen

Polyglycine is translated from the repeating sequence 5′−(GGU−GGC−GGA)𝑛−3′. If only one tRNA is needed to make polyglycine, what can you say about the tRNA anticodon?

1. The anticodon contains a wobble nucleotide. 

2.   The anticodon contains an adenosine: 5′−ACC.

3.   The anticodon contains an inosine: 5′−ICC.

4.   This is not possible; more than one tRNA is required in this situation.

The anticodon contains an inosine: 5′−ICC.

3. Which of the following statements about the bacterial ribosome is not true?

1. The 70S ribosome is a complex of 50S and 30S subunits. 

2.   The entire protein component of the 30S subunit is a single polypeptide chain. 

3.   Each ribosomal subunit contains at least one RNA molecule. 

4.   An rRNA molecule, rather than protein, catalyzes peptide bond formation.

  The entire protein component of the 30S subunit is a single polypeptide chain. 

Which of the following describes an accurate order of events in translation?

1. Ribosomal translocation occurs before the first aminoacyl-tRNA molecule binds to the small subunit. 

2.   Initiation of translation occurs only after the small subunit dissociates from the mRNA. 

3.   The large subunit of the ribosome binds the mRNA before the small subunit. 

4.   The first aminoacyl-tRNA molecule binds to the small subunit before the large subunit binds. 

The first aminoacyl-tRNA molecule binds to the small subunit before the large subunit binds. 

Given the wobble rules, what is the fewest number of tRNAs necessary to insert the amino acid Phe, and what is the anticodon for each tRNA? There are two codons that specify Phe: UUU and UUC.

1. One, with anticodon GAA 

2.   One, with anticodon AAA 

3.   One, with anticodon CAA 

4.   Two, with anticodons AAA and GAA 

One, with anticodon GAA 

6. Which one of the following experimental results does not support the hypothesis that the ribosome is a ribozyme?

a. There are no proteins observed within 18Å of the peptidyl transferase active site in the crystal structure. 

b. Peptidyl transferase activity is not inactivated by treating the ribosome with detergent. 

c. Peptidyl transferase activity can be inactivated by base changes in the rRNA. 

d. Ribosomes from thermophilic organisms are more stable than those from Escherichia coli.

d. Ribosomes from thermophilic organisms are more stable than those from Escherichia coli.

The enzyme that catalyzes the activation of tRNA molecules is:

1. the ribosome. 

2.   RNA polymerase. 

3.   tRNA isomerse. 

4.   aminoacyl-tRNA synthetase.

a. aminoacyl-tRNA synthetase.

The difference between a Class I and a Class II tRNA synthetase is:

1. the Class I synthetase requires ATP cofactor and the Class II does not. 

2.   the Class I synthetase uses the 2'-OH of 3' end of the tRNA as a nucleophile and the Class II uses the 3'-OH. 

3.   the Class II synthetase reaction requires a transesterification reaction not necessary in the Class I reaction. 

4.   the Class II synthetases are typically monomeric, whereas the Class I enzymes frequently function as multimeric protein complexes. 

1.   the Class I synthetase uses the 2'-OH of 3' end of the tRNA as a nucleophile and the Class II uses the 3'-OH. 

10. Name the type of chemical bonds that link an amino acid to tRNA.

1. Phosphodiester 

2.   Hydrogen 

3.   Amide or peptide 

4.   Ester 

Ester

11. A researcher isolates a mutant variant of the bacterial translation factor IF-2. The mutation allows proper folding of the protein and binding of GTP, but does not allow GTP hydrolysis. At what stage would translation be blocked by this mutant protein?

1. Binding of IF-2 to the ribosome. 

2.   Release of initiation factors and initiation of elongation. 

3.   Formation of the 70S ribosome. 

4.   Binding of fMet-tRNAfMet.

1.   Release of initiation factors and initiation of elongation. 

1. A housekeeping gene is one that codes for a product that:

1. functions in removing dirt from the cell. 

2.   is expressed differentially based on the needs of the cell. 

3.   is expressed at a constitutive level. 

4.   functions exclusively in cell membrane maintenance. 

is expressed at a constitutive level. 

The sequence of a promoter constitutes the most basic mechanism of transcription regulation because:

1.  promoters are always bound by activators. 

2.   RNA polymerase has differential affinities for different sequences that correlate with the efficiency of transcription. 

3.   promoters are always bound by repressors. 

4.   the expression levels of different housekeeping genes are always identical. 

RNA polymerase has differential affinities for different sequences that correlate with the efficiency of transcription. 

A transcription factor that enhances gene expression is called a(n):

1. repressor. 

2.   enhancer 

3.   operator 

4.   activator 

activator

4. Which of the following is the least likely mechanism for reducing the rate of gene transcription by a repressor?

1. The repressor binds directly to the RNA polymerase to block the closed-to-open transition at initiation. 

2.   The repressor induces a conformational change in the polymerase that accelerates the closed-to-open transition. 

3.   The binding of the repressor sterically occludes binding of the RNA polymerase to the promoter. 

4.   The repressor binds directly to the DNA to stabilize the closed complex over the open complex.

1.   The repressor induces a conformational change in the polymerase that accelerates the closed-to-open transition. 

Why are nuclear localization sequences (NLS) not removed after nuclear proteins are transported to the nucleus?

1. It is too energetically costly for the cell. 

2.   An NLS may be located almost anywhere along the primary sequence of the protein. 

3.   mRNA molecules are synthesized in the nucleus. 

4.   The nuclear envelope breaks down with each cell division.

1.   The nuclear envelope breaks down with each cell division.

Which of the following is not true of the process of nonsense-mediated mRNA decay?

1. Its function is to destroy mRNA molecules with premature stop codons. 

2.   The participation of the ribosome is not required. 

3.   It requires the marking of the mRNA before the mRNA is exported to the cytoplasm. 

4.   It involves the removal of the 5' cap of the mRNA. 

1.   The participation of the ribosome is not required. 

A researcher isolates a mutant variant of the bacterial translation factor EF-Tu. The mutation allows proper folding of the protein and binding of GTP, but does not allow GTP hydrolysis. What would be the first step in protein synthesis to be completely inhibited?

1. Binding of fMet-tRNAfMet to P site. 

2.   Formation of peptide bond between amino acids. 

3.   Second aminoacyl-tRNA binding to the ribosomal A site. 

4.   Movement of ribosome along the mRNA to allow binding of a new EF-Tu–tRNA in A site.

1.   Formation of peptide bond between amino acids. 

Which of the following statements is true of bacterial polysomes?

1. Translation can initiate with an mRNA before transcription of that mRNA is complete. 

2.   A single ribosome can translate multiple mRNA molecules at the same time. 

3.   Polysome formation ensures that only one polypeptide is translated per mRNA molecule. 

4.   Polysomes are membrane-bound compartments where translation occurs. 

1. Translation can initiate with an mRNA before transcription of that mRNA is complete. 

 Which of the following is not true of the translocation step of translational elongation in bacteria?

1. The deacylated tRNA is moved from the P site to the E site. 

2.   EF-G binds to the A site, mimicking a EF-Tu-aminoacyl-tRNA complex. 

3.   EF-G hydrolyzes GTP. 

4.   The peptidyl-tRNA moves from the P site to the A site. 

1.   The peptidyl-tRNA moves from the P site to the A site. 

1. Which of the following is not true of the lac operon?

1. Transcription produces a single polycistronic mRNA containing the lacZ, lacY, and lacA genes. 

2.   The lacI gene is controlled from the same promoter as the lacZ gene 

3.   The Lac repressor protein is constitutively expressed. 

4.   The operator region regulates transcription through interaction with the Lac repressor protein. 

1.   The lacI gene is controlled from the same promoter as the lacZ gene 

Which of the following describes the function of the lacO region of the lac operon?

1.   It encodes for the Lac repressor protein. 

2.   It contains the promoter for the operon. 

3.   Mutation of this region leads to constitutive expression of the operon. 

4.   It encodes for the galactoside permease protein. 

1.   Mutation of this region leads to constitutive expression of the operon. 

3. The enzyme that catalyzes the formation of allolactose from lactose is:

1. galactoside permease. 

2.   lactose isomerase. 

3.   thiogalactoside tranacetylase. 

4.   β-galactosidase. 

1.   β-galactosidase. 

A merodiploid is:

1. a haploid organism that contains a second copy of a part of its genome. 

2.   a haploid organism that is missing part of its genome. 

3.   a diploid organism that is missing part of its genome. 

4.   a diploid organism that contains another copy of its genome. 

1. a haploid organism that contains a second copy of a part of its genome. 

 The result obtained in Jacob and Monod’s merodiploid analysis that suggested the lacI region acts in trans to regulate the lac operon was:

1. a nonfunctional lacI mutant is rescued by a wild-type lacI allele. 

2.   a nonfunctional lacI mutant cannot be rescued by a wild-type lacI allele. 

3.   a nonfunctional lacO mutant is rescued by a wild-type lacO allele. 

4.   a nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

1. a nonfunctional lacI mutant is rescued by a wild-type lacI allele. 

The binding of _______________ to the Lac repressor causes the protein to dissociate from the operator.

1. lactose 

2.   glucose 

3.   fructose 

4.   allolactose 

1. allolactose

Which one of the following proteins is not required at low, basal levels for the regulation of the expression of the lac operon?

1. thiogalactoside transacetylase 

2.   galactoside permease 

3.   β-galactosidase 

4.   No answer text provided. 

1. thiogalactoside transacetylase 

Many riboswitches have been characterized in bacteria, including one that binds to thiamin E pyrophosphate (TPP) and another that binds to glucosamin E 6-phosphate. Which of the following accurately compares and contrasts the mechanisms by which these two riboswitches inhibit translation of their RNAs?

1. The TPP-binding riboswitch alters mRNA conformation when TPP is bound, creating RNA helices that prevent ribosome binding. The glucosamine 6-phosphate–binding riboswitch also changes the conformation of its mRNA, but in this case the change activates a ribozyme ribonuclease function that cleaves and inactivates the mRNA. 

2.   The TPP-binding riboswitch alters mRNA conformation when TPP is bound, and the change activates a ribozyme ribonuclease function that cleaves and inactivates the mRNA. The glucosamine 6-phosphate–binding riboswitch also changes the conformation of its mRNA, which prevents binding of ribosomes. 

3.   The TPP-binding riboswitch alters mRNA conformation when TPP is bound, rendering the Shine-Dalgarno sequence inaccessible to ribosome binding. The glucosamine 6-phosphate–binding riboswitch also changes the conformation of its mRNA, but in this case the change activates a ribozyme ribonuclease function that cleaves and inactivates the mRNA. 

4.   The TPP-binding riboswitch alters mRNA conformation when TPP is bound, rendering the Shine-Dalgarno sequence inaccessible to ribosome binding. The glucosamine 6-phosphate–binding riboswitch also changes the conformation of its mRNA, but in this case the change creates two RNA helices that prevent ribosome binding. 

3.   The TPP-binding riboswitch alters mRNA conformation when TPP is bound, rendering the Shine-Dalgarno sequence inaccessible to ribosome binding. The glucosamine 6-phosphate–binding riboswitch also changes the conformation of its mRNA, but in this case the change activates a ribozyme ribonuclease function that cleaves and inactivates the mRNA. 

How does the organization of related genes into operons enable the coordinated production of proteins in bacteria?

1. Genes are transcribed from one promoter. Transcription of the various mRNAs can be regulated by one set of activators and/or repressors, and each enzyme translated according to need. 

2.   Genes are transcribed together from one promoter as a polycistronic mRNA. They can be regulated by one set of activators and/or repressors and enzymes required for a common pathway can be synthesized together. 

3.   Genes are transcribed together from one promoter as a polycistronic mRNA. They can be regulated by one set of activators and/or repressors. Processing and possible splicing of this mRNA will allow enzymes to be translated according to need. 

4.   There is no coordination. 

1.   Genes are transcribed together from one promoter as a polycistronic mRNA. They can be regulated by one set of activators and/or repressors and enzymes required for a common pathway can be synthesized together. 

10. Consider the leader region of the trp mRNA. How would transcription of the E. coli trp operon be affected by removing sequence 4?

1. increased attenuation and thus decreased transcription 

2.   decreased attenuation and thus increased transcription 

3.   no attenuation, and thus transcription would proceed at the maximum level 

4.   none of the above 

1.   no attenuation, and thus transcription would proceed at the maximum level 

E. coli cells are growing in a medium containing lactose but no glucose. How would a mutation that prevents binding of CRP to its binding site near the Lac promoter affect expression of the lac operon?

1.  increase expression of the lac operon 

2.   decrease expression of the lac operon 

3.   not change expression of the lac operon 

4.   none of the above 

1.   decrease expression of the lac operon 

An amino acid most likely to be found in a reverse turn is:

 glycine

 valine

 leucine

 isoleucine

Glycine

A transcriptional repressor contains an amphipathic helix.  Which of the following changes within the repressor would most likely disrupt its function?

 serine to threonine

 aspartate to glutamate

 leucine to valine

 leucine to lysine

 leucine to lysine

Induced fit can be best described as the result of:

 mutations that increase ligand binding.

 an increase in Kd.

 the conformational change in protein due to binding to ligand.

 the conformational change of the ligand due to binding to protein.

 the conformational change in protein due to binding to ligand.

Successive nucleotides of a DNA chain are joined by:

phosphodiester bonds between the 5' carbon of one nucleotide and the 2' carbon of the next.

phosphodiester bonds between the 3' carbon of one nucleotide and the 5' carbon of the next.

ionic bonds between the phosphate group of one nucleotide and the sugar group of the next.

hydrogen bonds between the complementary bases.

phosphodiester bonds between the 3' carbon of one nucleotide and the 5' carbon of the next.

Which of the following is not a feature of the DNA helix proposed by Watson and Crick?

double-stranded

right-handed

antiparallel

two grooves of equal dimensions

two grooves of equal dimensions

Eukaryotic chromatin can be described in topological terms as a series of: 

constrained segments.

constrained loops.

relaxed segments.

relaxed loops.

constrained loops.

Histones:

have highly conserved sequences among eukaryotes.

are rich in basic amino acids; about 25% of the total amino acids are lysine and arginine.

contain a histone-fold motif comprised of three α-helices linked by two short loops.

All of these choices are correct.

All of these choices are correct.

Which of the following is true with regard to DNA primase?

It synthesizes the RNA primers required for lagging strand synthesis.

It is responsible for RNA primer removal and replacement with DNA.

It seals the gaps or nicks produced during lagging strand synthesis.

It is inhibited by the presence of the helicase.

It synthesizes the RNA primers required for lagging strand synthesis.

Which of the following pathways does not require DNA ligase?

gap repair

fork regression and resolution of a stalled replication fork

synthesis-dependent strand annealing

double-strand break repair

fork regression and resolution of a stalled replication fork

Which of the following are examples of biotechnology applications for site-specific recombination?

replacement of one gene allele for another on the chromosome

deletion of a gene from the chromosome

insertion of a new gene into a defined location on the chromosome

all of the choices given are correct.

all of the choices given are correct.

Which of the following is not a mechanism for regulating gene expression after the mature RNA transcript is produced?

gene silencing by miRNAs

inhibition of translation initiation

blockage of the promoter by a repressor protein

protein degradation

blockage of the promoter by a repressor protein