Cell Bio Question Bank Exam #2

Which molecule has a critical role in transcription elongation? (A)P-TEFb (B)HAT (C)miRNA (D)lncRNA

(A)P-TEFb

The first amino acid of eukaryotic polypeptides is (A)the amino acid encoded by the first 5ʹ codon. (B)Valine. (C)N-formylmethionine. (D)methionine.

(D)methionine.

Deamination of cytosine results in the conversion of cytosine to (A)Hypoxanthine. (B)Adenine. (C)7-methyl guanosine. (D)uracil​

(D)uracil​

Suppose an E. coli cell is in an environment that is rich in glucose and poor in lactose. Which statement best explains gene expression of enzymes used in lactose breakdown? (A)A repressor binds to the operator site of the lac operon and inhibits transcription of the genes involved in lactose breakdown. (B)The high levels of glucose cause a cascade that ends with CAP binding to RNA polymerase, which activates transcription of the genes involved in lactose breakdown. (C)Glucose binds to a repressor protein, which binds to the operator site and blocks RNA polymerase from transcribing the genes involved in lactose breakdown. (D)Glucose binds to the operator site of the lac operon, repressing transcription of the genes involved in lactose breakdown.

(A)A repressor binds to the operator site of the lac operon and inhibits transcription of the genes involved in lactose breakdown.

How does nucleotide-excision repair differ from base-excision repair? (A)Base-excision repair recognizes and removes single damaged bases, whereas nucleotide-excision repair is more general, recognizing many different kinds of lesions that distort the DNA molecule. (B)Nucleotide-excision repair reverses the chemical reaction that caused the lesion, whereas base-excision repair removes the damaged bases and replaces them with normal ones. (C)Only the base is removed in base-excision repair, whereas the entire nucleotide is removed in nucleotide-excision repair. (D)Base-excision repair requires no protein components and can occur by simple absorption of UV light, whereas nucleotide-excision repair requires several enzymes.

(A)Base-excision repair recognizes and removes single damaged bases, whereas nucleotide-excision repair is more general, recognizing many different kinds of lesions that distort the DNA molecule.

Which statement about translational initiation is false? (A)In prokaryotes, ribosomes often bind the mRNA and can scan 5ʹ or 3ʹ until recognizing a Shine-Dalgarno sequence. (B)Viral mRNAs contain internal ribosome entry sites that allow ribosomes to bind to an internal site of the mRNA. (C)Initiation codons in prokaryotic cells are preceded by Shine-Dalgarno sequences. (D)5ʹ 7-methylguanosine caps serve as the point of recognition and binding for ribosomes in eukaryotic cells.

(A)In prokaryotes, ribosomes often bind the mRNA and can scan 5ʹ or 3ʹ until recognizing a Shine-Dalgarno sequence.

Which rationale best describes the ability of an enhancer to mediate transcription from very distant sites? (A)Looping of the DNA can occur, allowing the transcription factor to come into proximity of the RNA polymerase. (B)When needed, enhancers are spliced into a region closer to the promoter. (C)They are recognized by RNA polymerase, which binds to the enhancers and then slides down the promoter toward the gene. (D)All of the above

(A)Looping of the DNA can occur, allowing the transcription factor to come into proximity of the RNA polymerase.

The function of aminoacyl tRNA synthetases is to (A)covalently attach amino acids to their corresponding tRNA molecules. (B)synthesize tRNA molecules. (C)catalyze the formation of the aminoacyl ATP intermediate during amino acid attachment to tRNAs. (D)catalyze the formation of a peptide bond between amino acids.

(A)covalently attach amino acids to their corresponding tRNA molecules.

A reporter gene is used to (A)identify regulatory sequences from the upstream regions of other genes. (B)determine if a protein binds to a given sequence element. (C)determine if a gene contains introns. (D)determine the stability of a protein.

(A)identify regulatory sequences from the upstream regions of other genes.

A ribozyme is defined as an enzyme (A)in which an RNA molecule is responsible for the catalytic activity. (B)that catalyzes the cleavage of RNA. (C)that is involved in translation. (D)that catalyzes the addition of ribose moieties to RNA.

(A)in which an RNA molecule is responsible for the catalytic activity.

In prokaryotes, sigma factors are necessary for (A)specific binding to certain promoter elements. (B)low-affinity binding upstream from promoters. (C)elongation of the RNA strand to its end. (D)faster transcription

(A)specific binding to certain promoter elements.

According to the central dogma of molecular biology, transcription of genetic information occurs via (A)DNA-dependent DNA synthesis. (B)DNA-dependent RNA synthesis. (C)RNA-dependent DNA synthesis. (D)RNA-dependent protein synthesis.

(B)DNA-dependent RNA synthesis.

Cells regulate gene expression to conserve which resource? (A)Water (B)Energy (C)Nucleotides (D)Amino Acids

(B)Energy

Chromatin remodeling factors are responsible for shuffling and rearranging DNA sequences in chromatin to make them either more or less accessible for transcription. (A)True (B)False

(B)False

True or False: The promoter sequence is transcribed first, followed by the DNA of the gene. (A)True (B)False

(B)False

In Drosophila, genes encoding heat shock proteins are normally not expressed but are arrested at an early transcription phase. However, if these organisms are exposed to sudden bursts of heat, transcription elongation is stimulated and the heat shock proteins are expressed. What is the most likely explanation that could account for this heat shock effect? (A)Heat causes repression of HAT expression. (B)Heat stimulates PTEFb expression. (C)Heat leads to dephosphorylation of the C terminal domain of RNA polymerase. (D)Heat causes expression of an inhibitor of PTEFb.

(B)Heat stimulates PTEFb expression.

5. In eukaryotic gene expression, how do promoters differ from enhancers? (A)Promoters are regulatory sequences that are usually far upstream from the coding region (B)Promoters are often active at low levels, allowing for a minimal level of gene expression, while enhancers are utilized only to up-regulate the level of gene expression. (C)Enhancers are strictly on/off regulatory elements, while promoters determine the level of transcription at any given time. (D)Promoters are typically able to bind only specific transcription factors, while a single enhancer may up-regulate several different genes.

(B)Promoters are often active at low levels, allowing for a minimal level of gene expression, while enhancers are utilized only to up-regulate the level of gene expression.

Which statement about the attachment of amino acids to tRNAs is false? (A)The amino acid is first joined to AMP, forming an aminoacyl AMP intermediate. (B)Two molecules of ATP are required for the process, one at each step. (C)Aminoacyl tRNA synthetases catalyze the reaction. (D)The amino acid is transferred to the 3ʹ end of the tRNA.

(B)Two molecules of ATP are required for the process, one at each step.

Ferritin expression is stimulated by iron because iron (A)stimulates a protein to bind the ferritin mRNA and inhibit its degradation. (B)stimulates the dissociation of a translational inhibitor from the ferritin mRNA. (C)binding stabilizes the ferritin protein. (D)stimulates the extension of poly-A tails of ferritin mRNAs.

(B)stimulates the dissociation of a translational inhibitor from the ferritin mRNA.

Which process both stabilizes and increases the efficiency of translation of an mRNA? (A)Editing (B)Splicing (C)Addition of a 7-methylguanosine cap (D)Addition of the CCA sequence to the 3ʹ end

(C)Addition of a 7-methylguanosine cap

mRNAs are degraded in the cytoplasm by (A)shortening of the poly-A tail and degradation from the 3′ end by nucleases. (B)removal of the 5′ cap and degradation from the 5′ end by nucleases. (C)Both a and b (D)Neither a nor b

(C)Both a and b

Which of the following statements regarding somatic hypermutation is false? (A)The enzyme activation-induced deaminase (AID) is a key player in somatic hypermutation. (B)Somatic hypermutation is thought to be the result of a high frequency of errors during DNA repair. (C)Somatic hypermutation is thought to control the proliferation of B lymphocytes by rendering their genome irreplicable. (D)Somatic hypermutation substantially increases affinity for antigen.

(C)Somatic hypermutation is thought to control the proliferation of B lymphocytes by rendering their genome irreplicable.

Which of the following statements about transcriptional termination in prokaryotes is false? (A)Termination is signaled by a GC-rich interval that forms a stem-loop structure in the RNA. (B)Transcription terminates when the RNA polymerase dissociates from its DNA template. (C)The ribosome comes to a UAA, UAG, or UGA stop codon and transcription ceases. (D)A segment of RNA forms a stable stem-loop structure by complementary base pairing.

(C)The ribosome comes to a UAA, UAG, or UGA stop codon and transcription ceases.

Some bacterial promoter regions are regulated by _______ that stimulate RNA polymerase binding and by _______ that block RNA polymerase binding. (A)inducers; suppressors (B)triggers; arrestors (C)activators; repressors (D)promoters; operators

(C)activators; repressors

The primary function of rRNAs in the ribosome is to (A)serve as a scaffold for the ribosomal proteins. (B)assist in the proper positioning of tRNAs along the mRNA template. (C)catalyze peptide bond formation. (D)assist in the proper folding of ribosomal proteins.

(C)catalyze peptide bond formation.

Eukaryotic transcriptional activators have activation domains that interact with (A)DNA binding domains. (B)enhancers and promoters. (C)mediator proteins and transcription factors (D)Histones

(C)mediator proteins and transcription factors

During mismatch repair in E. coli, the parental strand is recognized by (A)single-stranded breaks. (B)glycosylated adenines. (C)methylated adenines. (D)methylation of the O6 position of guanine residues.

(C)methylated adenines.

The initiator codon in prokaryotes is (A)the first codon located at the 5ʹ end of the mRNA. (B)recognized by scanning of the ribosome downstream of the 5ʹ 7-methylguanosine cap. (C)recognized via the Shine-Dalgarno sequence. (D)the first 5ʹ AUG of the mRNA.

(C)recognized via the Shine-Dalgarno sequence.

Which of the following RNAs is RNA polymerase II not responsible for transcribing? (A)mRNA (B)miRNA (C)tRNA (D)lncRNA

(C)tRNA

Which statement regarding tRNAs is false? (A)tRNAs are approximately 70-80 bases long and form a cloverleaf structure. (B)All tRNAs have a CCA sequence at their 3ʹ terminus. (C)tRNAs differ in sequence only at the anticodon. (D)There are several modified bases present in mature tRNAs.

(C)tRNAs differ in sequence only at the anticodon.

Which of the following enzymes serves an important role in both somatic hypermutation and class switch recombination? (A)Helicase (B)Exonuclease (C)DNA glycosylase (D)Activation-induced deaminase (E)Serine-threonine kinase

(D)Activation-induced deaminase

Estimates of mutation rates for a variety of genes indicate that the frequency of errors during replication is much lower than would be predicted on the basis of complementary base pairing. What accounts for the higher degree of fidelity? (A)Conformational changes in DNA polymerase (B)3ʹ to 5ʹ exonuclease activity of DNA polymerase (C)Requirement of a primer for DNA synthesis by DNA polymerase (D)All of the above

(D)All of the above

Which statement about cis-acting elements is true? (A)They are specific DNA sequences that control the transcription of adjacent genes. (B)Various proteins specifically recognize and bind to these cis-acting sequences. (C)They may be directly adjacent to the gene they control or far away. (D)All of the above

(D)All of the above

Which is a mechanism of histone change that is mediated by chromatin remodeling factors? (A)Proteolytic breakdown of histone proteins (B)Acetylation of histone proteins (C)Ubiquitination of histone proteins (D)Conformational change of histone tertiary structure

(D)Conformational change of histone tertiary structure

What is the major difference between histone modification and chromosome remodeling? (A)Histone modification enzymes excise nucleosomes from the chromatin while chromatin remodeling enzymes add phosphate, acetyl, or methyl groups to the entire nucleosome. (B)The histone modification enzymes remove methyl and acetyl groups from nucleosomes, and chromosome remodeling enzymes replace them. (C)Histone modification enzymes recruit repressors and activators, while chromosome remodeling enzymes recruit corepressors and coactivators. (D)Histone modification enzymes add side groups to the nucleosome proteins, while chromosome remodeling enzymes move, alter, or remove entire nucleosomes.

(D)Histone modification enzymes add side groups to the nucleosome proteins, while chromosome remodeling enzymes move, alter, or remove entire nucleosomes.

The lac operon is regulated by both a positive transcriptional control system and a negative transcriptional control system. Under what conditions will both systems operate to stimulate transcription of the lac operon? (A)High glucose and high allolactose (B)Low glucose and low allolactose (C)High glucose and low allolactose (D)Low glucose and high allolactose

(D)Low glucose and high allolactose

Which statement about pyrimidine dimers is false? (A)They are lesions in DNA caused by UV radiation. (B)They are formed between adjacent pyrimidines on a DNA strand. (C)Their formation blocks DNA replication and transcription. (D)They can be repaired by photoreactivation in human cells.

(D)They can be repaired by photoreactivation in human cells.

The 5′ end of messenger RNA is modified by (A)Polyadenylation. (B)polyribothymidine addition. (C)capping with methylation. (D)capping with 7-methylguanosine.

(D)capping with 7-methylguanosine.

The lac operon in E. coli is regulated by lactose, which (A)activates an activator of transcription. (B)inactivates an activator of transcription. (C)activates a repressor of transcription. (D)inactivates a repressor of transcription.

(D)inactivates a repressor of transcription.