Final Exam Flashcards
The primary mechanism responsible for variations in the level of constitutive enzymes from different genes is that:
A. all constitutive enzymes are synthesized at the same rate, but are not degraded equally.
B. their promoters have different affinities for RNA polymerase holoenzyme.
C. some constitutively expressed genes are more inducible than others.
D. some constitutively expressed genes are more repressible than others.
E. the same number of mRNA copies are made from each gene, but are translated at different
rates.
B. their promoters have different affinities for RNA polymerase holoenzyme
- The σ (sigma) subunit of E. coli RNA polymerase holoenzyme is an example of a (an)
A. repressor
B. activator
C. specificity factor
D. effector
C. specificity factor
Which of the following statements correctly describes promoters in E. coli?
A. A promoter may be present on either side of a gene or in the middle of it.
B. All promoters have the same sequence that is recognized by RNA polymerase holoenzyme.
C. Every promoter has a different sequence, with little or no resemblance to other promoters.
D. Many promoters are similar and resemble a consensus sequence, which has the highest affinity for RNA polymerase holoenzyme.
E. Promoters are not essential for gene transcription, but can increase its rate by two- to three- fold.
D. Many promoters are similar and resemble a consensus sequence, which has the highest affinity for RNA polymerase holoenzyme.
Operons consist of
A. a group of clustered genes, a promoter, and regulatory sequences.
B. a group of clustered genes and a promoter.
C. a group of clustered genes.
D. groups of genes controlled by a common regulator.
A. a group of clustered genes, a promoter, and regulatory sequences
Beta-galactosidase does not catalyze
A. the cleavage of allolactose.
B. the cleavage of IPTG.
C. the conversion of lactose to allolactose.
D. the cleavage of lactose.
B. the cleavage of IPTG
The operator region normally can be bound by:
(Slide.. The negative regulation of lac operon)
A. attenuator. B. inducer. C. mRNA. D. repressor. E. suppressor tRNA.
D. repressor.
Small signal molecules that regulate transcription are not known to:
A. cause activator proteins to bind DNA sites.
B. cause repressor proteins to bind DNA sites.
C. directly bind to DNA sites.
D. prevent activator proteins from binding to DNA sites.
E. release repressor proteins from DNA sites.
C. directly bind to DNA sites.
Under what conditions is the E. coli lactose (lac) operon expressed?
(Slide.. Combined effects of glucose and lactose)
A. When glucose and lactose concentrations are low.
B. When galactose concentrations are high and glucose concentrations are low.
C. When lactose concentrations are low and glucose concentrations are high.
D. When glucose concentrations are low and lactose concentrations are high.
D. When glucose concentrations are low and lactose concentrations are high.
Transcription of the lactose operon in E. coli is stimulated by:
(Slide.. The trp Operon - dual control)
A. a mutation in the repressor gene that strengthens the affinity of the repressor for the operator.
B. a mutation in the repressor gene that weakens the affinity of the repressor for the operator.
C. a mutation in the repressor gene that weakens the affinity of the repressor for the inducer.
D. binding of the repressor to the operator.
E. the presence of glucose in the growth medium.
B. a mutation in the repressor gene that weakens the affinity of the repressor for the operator.
The DNA binding motif for many prokaryotic regulatory proteins, such as the lac repressor, is:
(Slide.. Helix Turn Helix Motif is common in DNA Binding proteins)
A. helix-turn-helix. B. homeobox. C. homeodomain. D. leucine zipper. E. zinc finger.
A. helix-turn-helix
The leucine zipper motif mediates
(Slide.. Leucine zipper - dimerization domains)
A. DNA binding.
B. transcriptional attenuation.
C. protein-protein interactions.
D. RNA binding.
C. protein-protein interactions.
Protein structural motifs often have general functions in common. Which one of the following motifs is known to be involved in protein dimer formation, but not in direct protein-DNA interactions?
(Slide.. Leucine zipper - dimerization domains)
A. β-barrel B. helix-turn-helix C. homeodomain D. leucine zipper E. zinc finger
D. leucine zipper
Which of the following statements about regulation of the lac operon is true?
(Slide.. Positive regulation of Lac operon by CRP)
A. Glucose in the growth medium decreases the inducibility by lactose.
B. Glucose in the growth medium does not affect the inducibility by lactose.
C. Glucose in the growth medium increases the inducibility by lactose.
D. Its expression is regulated mainly at the level of translation.
E. The lac operon is fully induced whenever lactose is present.
A. Glucose in the growth medium decreases the inducibility by lactose.
The binding of CRP (cAMP receptor protein of E. coli) to DNA in the lac operon:
(Slide.. Positive regulation of Lac operon by CRP)
A. assists RNA polymerase binding to the lac promoter.
B. is inhibited by a high level of cAMP.
C. occurs in the lac repressor region.
D. occurs only when glucose is present in the growth medium.
E. prevents repressor from binding to the lac operator
A. assists RNA polymerase binding to the lac promoter.
Consider the lac operon of E. coli. When there is neither glucose nor lactose in the growth medium:
(Slides.. Combined effects of glucose and lactose.. CAP=CRP)
A. CRP protein binds to the lac operator.
B. CRP protein displaces the Lac repressor from the lac promoter.
C. CRP binds to the CRP site near the promoter and repressor is bound to the lac operator.
D. RNA polymerase binds lac promoter and transcribes the lac operon.
E. the operon is fully induced.
C. CRP binds to the CRP site near the promoter and repressor is bound to the lac operator.
When the growth medium contains both lactose and glucose, what proteins will bind to the lac operon regulatory region?
(Slides.. Combined effects of glucose and lactose.. CAP=CRP)
A. Neither Lac repressor nor CRP will bind.
B. Lac repressor will bind to the operon regulatory region but not CRP.
C. Lac repressor will not bind, but CRP will.
D. Both Lac repressor and CRP will bind to corresponding regions.
E. From the situation described, we cannot decide.
A. Neither Lac repressor nor CRP will bind.
E. coli cells are placed in a growth medium containing lactose. Indicate which of the following circumstances would increase the expression of the lactose operon.
(Slides.. Combined effects of glucose and lactose.. CAP=CRP)
A. Decrease the level of glucose to almost zero.
B. A Lac repressor mutation that prevents dissociation of Lac repressor from the operator
C. A mutation that inactivates β-galactosidase (the enzyme that also converts lactose into
allolactose).
D. A mutation that inactivates galactoside permease (the enzyme that normally allows external
lactose to enter the cell).
E. A mutation that prevents binding of CRP to its binding site near the lac promoter.
A. Decrease the level of glucose to almost zero.
A regulon is a(n):
(Slides.. Combined effects of glucose and lactose.. CAP=CRP)
A. group of related triplet codons.
B. network of operons with a common regulator.
C. operon that is subject to regulation.
D. protein that regulates gene expression.
E. ribosomal protein that regulates translation.
B. network of operons with a common regulator.
The tryptophan operon of E. coli is repressed by tryptophan added to the growth medium. The tryptophan repressor probably:
(Slide.. The trp Operon - dual control)
A. binds to RNA polymerase when tryptophan is present.
B. binds to the trp operator in the absence of tryptophan.
C. binds to the trp operator in the presence of tryptophan.
D. is a DNA sequence.
E. is an attenuator.
C. binds to the trp operator in the presence of tryptophan.
Which one of the following statements about the transcriptional attenuation mechanism is true?
A. In some operons (e.g., the His operon), attenuation may be the only regulatory mechanism.
B. Sequences of the trp operon leader RNA resemble an operator.
C. The leader peptide acts by a mechanism that is similar to that of a repressor protein.
D. The leader peptide gene of the trp operon includes no Trp codons.
E. The leader peptide is an enzyme that catalyzes transcription attenuation.
A. In some operons (e.g., the His operon), attenuation may be the only regulatory mechanism.
Which of the following statements is true of the attenuation mechanism used to regulate the tryptophan biosynthetic operon in E. coli?
(Slide.. Transcriptional attenuation in the trp operon)
A. Attenuation is the only mechanism used to regulate the trp operon.
B. One of the enzymes in the Trp biosynthetic pathway binds to the mRNA and blocks
translation when tryptophan levels are high.
C. The leader peptide directly binds to the operator causing RNA polymerase to attenuate transcription.
D. Trp codons in the leader peptide gene allow the system to respond to tryptophan levels in the cell.
E. When tryptophan levels are low, the trp operon transcripts are attenuated (halted before the operon’s structural genes are transcribed).
D. Trp codons in the leader peptide gene allow the system to respond to tryptophan levels in the cell.
Transcriptional attenuation in the trp operon of E. coli:
A. can adjust transcription of the structural genes upwards when tryptophan is present.
B. can fine-tune the transcription of the operon in response to small changes in Trp availability.
C. is a mechanism for inhibiting translation of existing complete trp mRNAs.
D. results from the binding of the Trp repressor to the operator.
E. results from the presence of short leader peptides at the 5’ end of each structural gene.
B. can fine-tune the transcription of the operon in response to small changes in Trp availability.
An example of coordinate control is the downegulation of ribosomal RNA synthesis in response to amino acid starvation, which will cause synthesis of ribosomal proteins to be limited. What is the correct order of the following events that participate in the signaling process?
(Slide.. Stringent response in E. coli. To amino acid starvation)
- Binding of stringent factor to the ribosome.
- Formation of the unusual nucleotide ppGpp (magic spot I).
- Formation of the unusual nucleotide pppGpp (magic spot II).
- Uncharged tRNA binds in the ribosomal A-site.
4,1,3,2
Which one of the following statements about eukaryotic gene regulation is correct?
A. Large polycistronic transcripts are common.
B. Most regulation is positive, involving activators rather than repressors.
C. Transcription and translation are mechanistically coupled.
D. Transcription does not involve promoters.
E. Transcription occurs without major changes in chromosomal organization.
B. Most regulation is positive, involving activators rather than repressors.
Enhancers are DNA sequences that enhance transcription of genes
(Slide.. Enhancers can be far away from the promoters in eukaryotes)
A. regardless of their orientation in the DNA.
B. only if located within a hundred base pairs of a gene’s transcription start site.
C. in prokaryotes and lower eukaryotes.
D. only if located upstream from a gene’s transcription start site.
A. regardless of their orientation in the DNA.
Which one of the following is NOT involved in steroid hormone action?
(Slide.. Typical steroid hormone receptors)
A. Cell surface receptors B. Hormone-receptor complexes C. Specific DNA sequences D. Transcription activation and repression E. Zinc fingers
A. Cell surface receptors
How do steroid hormones alter gene expression?
A. They bind to plasma membrane receptors that bring about the activation of the cAMP
receptor protein (CRP).
B. They act through a hormone-receptor complex that binds specific DNA sequences.
C. They bind specific DNA sequences and transactivate transcription.
D. They inactivate repressor molecules.
B. They act through a hormone-receptor complex that binds specific DNA sequences.
What are the mechanisms of translational repression that are known to exist in eukaryotes?
(Slide.. Translation regulation of eukaryotic mRNA)
A. inactivation of initiation factors usually by phosphorylation;
B. binding of repressor proteins to the mRNA, thereby interfering with initiation factors or the
ribosome;
C. interference with translation by microRNAs.
D. all of above
E. none of above
D. all of above
In eukaryotes, translational repressor proteins
(Slide.. Translation regulation of eukaryotic mRNA)
A. bind the initiating AUG codon of mRNAs and block the ribosome from initiating translation.
B. bind the 3′ untranslated region of mRNAs and interact with translation initiation factors to prevent translation initiation.
C. target mRNAs for degradation by ribonucleases.
D. modify particular residues of the mRNA and prevent its translation.
B. bind the 3′ untranslated region of mRNAs and interact with translation initiation factors to prevent translation initiation.
Micro-RNAs (miRNAs) and small temporal RNAs (stRNAs) inhibit the expression of specific genes by
(Slide.. MicroRNA regulates mRNA stability & transcription)
A. methylating the genes to prevent their transcription.
B. base pairing with the genes to prevent their transcription.
C. activating D Nases to destroy those genes.
D. targeting their mRNAs for degradation or by inhibiting their translation.
D. targeting their mRNAs for degradation or by inhibiting their translation
Which of the following statements about microRNA is INCORRECT?
(Slide.. MicroRNA regulates mRNA stability & transcription)
A. Their precursors(pre-miRNAs) are about 70 nucleotides long, withself-complementary internal sequences that can form hairpin structures.
B. These precursors are cleaved by endonucleases such as Dicers into 20-25 nucleotide partial miRNA duplexes.
C. Partial miRNA duplexes are separated into single strands and go into RISC.
D. RISC helps one strand to find the complementary mRNA strand and form hybrids which can then blocks translation or facilitates mRNA degradation.
E. Mature miRNA will pair with mRNA targets only if they have a perfect match
E. Mature miRNA will pair with mRNA targets only if they have a perfect match
Which one of the following is true about the genetic code?
A. All codons recognized by a given tRNA encode different amino acids.
B. It is absolutely identical in all living things.
C. Several different codons may encode the same amino acid.
D. The base in the middle position of the tRNA anticodon sometimes permits
“wobble” base pairing with 2 or 3 different codons.
E. The first position of the tRNA anticodon is always adenosine.
C. Several different codons may encode the same amino acid.
The genetic code has all of the following characteristics except:
(Slide.. Every nucleotide sequence has 6 potential reading farmers)
A. It is degenerate.
B. It is read 3’to5’.
C. It is read from a fixed starting point without punctuation.
D. It is not overlapping.
E. A group of three bases codes for one amino acid.
B. It is read 3’ to 5’.
What does it mean when the genetic code is described as “degenerate?”
(Slide.. Degeneracy is the redundancy of the genetic code)
A. It means that the translation machinery is prone to making errors.
B. It means that there are fewer codons than amino acids.
C. It means that two or more anticodons can base pair with the same codon.
D. It means that more than one codon can specify the same amino acid.
D. It means that more than one codon can specify the same amino acid.
Which of the following are features of the wobble hypothesis?
(Slide.. Table 27-4)
A. A naturally occurring tRNA exists in yeast that can read both arginine and lysine codons.
B. A tRNA can recognize only one codon.
C. Some tRNAs can recognize codons that specify two different amino acids, if both are nonpolar.
D. The “wobble” occurs only in the first base of the anticodon.
E. The third base in a codon always forms a normal Watson-Crick base pair.
C. Some tRNAs can recognize codons that specify two different amino acids, if both are nonpolar.
Wobble can occur because
(Slide.. Inosinate in anticodon in some tRNA is “Wobble”)
A. aminoacyl-tRNA synthetases can recognize more than one tRNA.
B. more than one codon can specify the same amino acid.
C. tRNAs contain the nucleotide inosinate.
D. more than one tRNA can be dedicated to an amino acid.
C. tRNAs contain the nucleotide inosinate.
Which of the following statements about tRNA molecules is false?
(Slide.. Inosinate in anticodon in some tRNA is “Wobble”)
A. A, C, G, and U are the only bases present in the molecule.
B. Although composed of a single strand of RNA, each molecule contains several short, double-helical
regions.
C. Any given tRNA will accept only one specific amino acid.
D. The amino acid attachment is always to an A nucleotide at the 3’ end of the molecule.
E. There is at least one tRNA for each of the 20 amino acids.
A. A, C, G, and U are the only bases present in the molecule.
RNA editing can be accomplished by?
(Slide.. mRNA are edited before protein synthesis)
A. splicing. B. deamination. C. translational frameshifting. D. addition or removal of nucleotides. E. Both B and D.
E. Both B and D.
Aminoacyl-tRNA synthetases (amino acid activating enzymes):
(Slide.. Aminoacyl-tRNA synthetase)
A. “recognize” specific tRNA molecules and specific amino acids.
B. in conjunction with another enzyme attach the amino acid to the tRNA.
C. interact directly with free ribosomes.
D. occur in multiple forms for each amino acid.
E. require GTP to activate the amino acid.
A. “recognize” specific tRNA molecules and specific amino acids.
In E. coli, how many amino-acyl tRNA synthetase enzymes are there?
(Slide.. Aminoacyl-tRNA synthetase)
A. 5 B. 10 C. 20 D. 32 E. 64
C. 20
What happens when Cys-tRNAcys is chemically modified to Ala-tRNAcys?
A. ribosome rejects the “wrong” aa-tRNA
B. Alanine is used, at Alanine codons only
C. Alanine is incorporated at Cysteine codons
D. No effect on anything
C. Alanine is incorporated at Cysteine codons
Which of the following statements about ribosomes is true?
A. There are two major subunits (a big subunit and a small subunit), each with multiple proteins.
B. They are relatively small, with molecular weights less than 10,000.
C. The large subunit contains rRNA molecules, the small subunit does not.
D. There are about 25 of them in an E. coli cell.
E. They have specific, different binding sites for each of the 20 tRNAs.
A. There are two major subunits (a big subunit and a small subunit), each with multiple proteins.
Proteins are made starting from:
A. the amino end and proceeding toward the carboxyl end
B. the carboxyl end and proceeding toward the amino end
C. the middle and proceeding toward both amino and carboxyl end
D. the 3’ end toward the 5’ end
E. the 5’ end toward the 3’ end
A. the amino end and proceeding toward the carboxyl end
Which of the following is true about the difference between translation in prokaryotes and eukaryotes?
A. Only prokaryotes have an initiation factor that binds the 5′ cap structure on mRNAs.
B. A Shine-Dalgarno sequence is needed for initiation of only eukaryotic mRNAs.
C. Translation and transcription are coupled only in prokaryotes.
D. Only eukaryotic mRNAs initiate with a residue of N-formylmethionine.
C. Translation and transcription are coupled only in prokaryotes.
What is the role of the Shine-Dalgarno sequence?
(Slide.. Translation in bacteria: initiation 1)
A. It marks the polypeptide for translocation into the lumen of the endoplasmic reticulum.
B. It targets proteins for degradation.
C. It guides the 30S ribosome to the initiating (5′) AUG of the mRNA.
D. It acts as a signal for the termination of translation.
C. It guides the 30S ribosome to the initiating (5′) AUG of the mRNA.
- The prokaryotic mRNA has a sequence like AGGAG (Shine-Dalgarno sequence) which binds to a sequence near the
(Slide.. Consensus (cis-Acting) initiation site in prokaryotic mRNA)
A. 3' end of 5S rRNA B. 3' end of 23S rRNA C. 3' end of 16S rRNA D. 3' end of tRNA E. 3' end of mRNA
C. 3’ end of 16S rRNA
- Which “factor” brings f-Met-tRNAF to the 30S initiation complex?
(Slide.. Translation in Bacteria: initiation 1)
A. IF-1 B. IF-2 C. IF-3 D. RF-2 E. EF-7
B. IF-2
During Initiation of Translation in E. coli, where does f-Met-tRNAF bind?
(Slide.. Translation in Bacteria: initiation 1)
A. The A site B. EF-Ts C. The P site D. RF-II E. The exit site
C. The P site
