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Which of the following statements best defines the term operon?
An operon is a region of DNA that consists of a single gene regulated by more than one promoter.
An operon is a region of RNA that consists of the coding regions of more than one gene.
An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter.
An operon is a region of DNA that codes for sugar-metabolizing enzymes.
An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter.
This arrangement of genes is common in bacteria. For example, genes involved in lactose metabolism are clustered in the lac operon of E. coli, and genes involved in tryptophan metabolism are in the trp operon.
What molecule binds to promoters in bacteria and transcribes the coding regions of the genes?
DNA polymerase
A nucleotide
RNA polymerase
DNA ligase
RNA Polymerase
RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.
What is allosteric regulation?
In allosteric regulation, genes are expressed constitutively.
In allosteric regulation, a gene is turned off by a repressor protein.
In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity.
In allosteric regulation, a gene is turned on by an activator protein.
In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity.
Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators
What happens to the expression of the lacI gene if lactose is not available in the cell?
There is no change—the lacI gene is constitutively expressed.
The lacI gene turns off.
The lacI gene increases its rate of transcription.
The lacI gene turns on.
There is no change—the lacI gene is constitutively expressed.
The lacI gene is expressed regardless of the presence of lactose. Only the structural genes of the lac operon are affected by the presence or absence of lactose.
The lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. When lactose is present in the cell, the cell expresses lacZ and metabolizes lactose.
Which of the following enzymes converts ATP to cAMP?
ATP synthase
b-galactosidase
Galactoside permease
Adenylyl cyclase
adenylyl cyclase
Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.
True or false? The mechanism by which glucose inhibits expression of the lac structural genes is known as catabolite stimulation, whereas the mechanism by which lactose stimulates expression of the lac structural genes is known as allosteric regulation.
True
False
False
The process by which lactose binds to the lac repressor and inactivates it by causing it to change shape is known as allosteric regulation. However, the process by which glucose causes cAMP levels in the cell to drop, thereby preventing CAP from stimulating expression of the lac structural genes, is known as catabolite repression.
Which of the following mutations could lead to constitutive expression of the genes of the lac operon?
A mutation in the lac-Z gene
A mutation in the lac-Y gene
A mutation in the operator sequence
A super repressor mutation
A mutation in the operator sequence
Such a mutation could prevent binding of the repressor, allowing expression under all conditions.
Which of the following best describes the biological role of the lac operon?
It prevents other sugars from being metabolized until all available lactose has been used.
It ensures that a cell produces enzymes involved in lactose metabolism in a constitutive manner.
It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.
It ensures that bacterial cells produce lactose only when no other food sources are available.
It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.
The cell expends energy to produce the proteins necessary for lactose metabolism only when lactose is present.
The placement of the operator sequence between the promotor and the structural genes is critical to the proper function of the lac operon.
True
False
True
When the repressor binds to the operator, RNA polymerase cannot transcribe the structural genes.
A. Polymerase escapes
B. the closed complex transitions to the open complex around the start site of transcription
C. the closed complex forms
D. the initial transcribing complex forms
E. repeated transcription of ~9 nucleotides occur
F. RNA polymerase binds to the promoter
A. Replication
B. Transcription
C. Translocation
D. Translation
DNA is transcribed to give an RNA copy.
A. Organelles
B. DNA
C. Messenger RNA
D. Proteins
Synthesis of organelles is not directly coded in the DNA.
A. A site where many different proteins will bind
B. A site found on the RNA polymerase
C. A site in DNA that recruits the RNA Polymerase
D. A nontranscribed sequence on the DNA
E. Part of the RNA molecule itself
This is the site where the RNA polymerase must bind to initiate transcription.
A. The promoter is a site at which only RNA polymerase will bind.
B. The promoter is a site found on RNA polymerase.
C. The promoter is a nontranscribed region of a gene.
D. The promoter is part of the RNA molecule itself.
The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.
A. The order of the chemical groups in the backbone of the RNA molecule
B. Base pairing between the two DNA strands
C. Base pairing between the DNA template strand and the RNA nucleotides
D. The previous base
Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.
A. Identical
B. Covalently bound
C. Complementary
D. Permanently base-paired
Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.
A. It is free to bind to another promoter and begin transcription.
B. It joins with another RNA polymerase to carry out transcription.
C. It is degraded.
D. It begins transcribing the next gene on the chromosome.
The enzyme is free to transcribe other genes in the cell.
One α-helix from σ region 2 recognizes and binds the -10 element of the promoter and uses several of its aromatic amino acids to stabilize the melted DNA. A helix-turn-helix from σ region 4 recognizes and binds the -35 element.
A. One α-helix from σ region 2 recognizes and binds the -35 element of the promoter and uses several of its aromatic amino acids to stabilize the melted DNA.
B. One α-helix from σ region 2 recognizes and binds the -10 element; a helix-turn-helix from σ region 4 recognizes and binds the -35 element.
C. One α-helix from σ region 2 recognizes and binds the -10 element; a helix-turn-helix from σ region 4 recognizes and binds the -35 element; αCTD binds to the UP-element.
The role for the α-helix from σ region 2 is more complicated than for the helix-turn-helix in σ region 4. The helix from region 2 has two functions: to recognize and bind the -10 element and also to interact with non-template bases using several of its aromatic amino acids in order to stabilize the melted DNA. The two α-helices from σ region 4 that form the helix-turn-helix motif are only needed to recognize and bind the -35 element. Recognition of the -35 element is accomplished by one of the helices inserting into the major groove to contact the edges of the bases. The other helix makes non-specific contacts with the DNA backbone to provide additional bonding strength.
A. any uncharged tRNA
B. any tRNA covalently attached to an amino acid at the 5′ end of the tRNA
C. any tRNA with a 5′-CCA-3′ sequence at the 3′ end of the tRNA
D. any tRNA covalently attached to an amino acid at the 3′ end of the tRNA
D. any tRNA covalently attached to an amino acid at the 3′ end of the tRNA
Charged tRNAs are covalently attached to the correct amino acid through an acyl linkage at the 3′ end of the tRNA, hence the name aminoacyl-tRNA. Charging is carried out by aminoacyl tRNA synthetases.
A codon is a group of three bases that can specify only one amino acid.
A. Addition and deletion mutations disrupt the primary structure of proteins.
B. An addition mutation results in an added base in the DNA sequence.
C. A deletion mutation results in the loss of a base in the DNA sequence.
D. A knock-out mutation results in a total absence of the mutated protein.
A. Both addition and deletion.
B. None.
C. Deletion.
D. Addition.
The original sequence has lost the base C.
A. One addition and two deletion mutations.
B. One addition and one deletion mutation.
C. One addition mutation.
D. One deletion mutation.
This combination results in no net change in the number of bases, so the reading frame would eventually be restored.
A. One.
B. None.
C. Two.
D. Three.
The second and third codons in the new sequence are different from the original codons.
A. An addition mutation and a deletion mutation.
B. None.
C. An addition mutation
D. A deletion mutation.
If the mutations occur within the same codon, only that codon (amino acid) will be altered
A. the initiating methionine is not an amino acid
B. its tRNA anticodon is not complementary to the AUG codon
C. a formyl group is attached to the initiating methionine
D. incorporation of the initial methionine does not require a tRNA
This modification is not present on methionine residues added during elongation.
A. complementary base pairing between mRNA and DNA
B. complementary base pairing between mRNA and tRNA
C. association of the 30S and the 50S ribosomal subunits
D. complementary base pairing between mRNA and rRNA
Transcription, not translation, is dependent on this association.
A. The large ribosomal subunit binds to the small ribosomal subunit.
B. The large ribosomal subunit binds to an mRNA sequence near the 5′ end of the transcript
C. The small ribosomal subunit binds to an mRNA sequence near the 3′ end of the transcript.
D. The small ribosomal subunit binds to an mRNA sequence near the 5′ end of the transcript
A. A Site, S Site, E Site
B. A Site, P Site, E Site
C. A Site, P Site, E Site, S Site
D. P Site, E Site, A Site
A. is attached through hydrogen bonds to the mRNA
B. is attached to the tRNA occupying the E site
C. is attached to the tRNA occupying the A site
D. is free in the cytoplasm
A. It requires GTP.
B. It is catalyzed by an enzymatic protein.
C. It is catalyzed by peptidyl transferase.
D. It uses water.
A. An operon is a region of RNA that consists of the coding regions of more than one gene.
B. An operon is a region of DNA that codes for sugar-metabolizing enzymes.
C. An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter.
D. An operon is a region of DNA that consists of a single gene regulated by more than one promoter.
This arrangement of genes is common in bacteria. For example, genes involved in lactose metabolism are clustered in the lac operon of E. coli, and genes involved in tryptophan metabolism are in the trp operon.
A. DNA polymerase
B. DNA ligase
C. RNA polymerase
D. A nucleotide
RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.
A. In allosteric regulation, a gene is turned on by an activator protein.
B. In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity.
C. In allosteric regulation, a gene is turned off by a repressor protein.
D. In allosteric regulation, genes are expressed constitutively.
Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators.
A. No glucose, high lactose
B. No glucose, no lactose
C. High glucose, no lactose
D. High glucose, high lactose
When glucose is absent and lactose levels are high, the lac structural genes are expressed the most efficiently. Without glucose, cAMP is produced and CAP can stimulate transcription of the structural genes. In the presence of lactose, the repressor does not bind to the operator and therefore does not block transcription.
A. There is no change—the lacI gene is constitutively expressed.
B. The lacI gene turns off.
C. The lacI gene increases its rate of transcription.
D. The lacI gene turns on.
The lacI gene is expressed regardless of the presence of lactose. Only the structural genes of the lac operon are affected by the presence or absence of lactose.
A. This gene encodes the repressor of the lac operon.
B. This gene encodes an enzyme, galactoside permease, which transports lactose into the cell.
C. This gene encodes an enzyme, b-galactosidase, which cleaves lactose into glucose and galactose.
D. This gene encodes an enzyme, b-galactosidase, that cleaves lactose into two glucose molecules.
The lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. When lactose is present in the cell, the cell expresses lacZ and metabolizes lactose.
A. b-galactosidase
B. Galactoside permease
C. Adenylyl cyclase
D. ATP synthase
Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.
The process by which lactose binds to the lac repressor and inactivates it by causing it to change shape is known as allosteric regulation. However, the process by which glucose causes cAMP levels in the cell to drop, thereby preventing CAP from stimulating expression of the lac structural genes, is known as catabolite repression.
A. A mutation in the operator sequence
B. A mutation in the lac-Z gene
C. A mutation in the lac-Y gene
D. A super repressor mutation
Such a mutation could prevent binding of the repressor, allowing expression under all conditions.
A. It ensures that a cell dedicates resources to the production of enzymes involved in lactose metabolism only when lactose is available in the environment.
B. It ensures that a cell produces enzymes involved in lactose metabolism in a constitutive manner.
C. It prevents other sugars from being metabolized until all available lactose has been used.
D. It ensures that bacterial cells produce lactose only when no other food sources are available.
The cell expends energy to produce the proteins necessary for lactose metabolism only when lactose is present.
A. True
B. False
When the repressor binds to the operator, RNA polymerase cannot transcribe the structural genes.
A. Constitutive expression means that the genes in the araBAD operon are expressed in the absence of arabinose.
B. Constitutive expression means that the genes in the araBAD operon are expressed in the presence of arabinose.
C. Constitutive expression means that the genes in the araBAD operon are expressed in the presence or absence of arabinose.
D. None of the above.
A. only when an activator binds
B. when an activator and repressor bind
C. only if the expression of the gene is regulated by a repressor
D. in the absence of activator and repressor binding
In the absence of activator and repressor binding, RNA polymerase will sometimes weakly bind the promoter and spontaneously transition into an open complex in which the DNA at the start site of transcription is unwound. This will initiate a low level of constitutive transcription producing the basal level of transcription.
A. TFIID/TBP → TFIIA → TF11B → TFIIF/RNA Pol II → TFIIE → TFIIH
B. TFIIA → TF11B → TFIID/TBP → TFIIF/RNA Pol II → TFIIE → TFIIH
C. TFIIA → TF11B → TFIID/TBP → TFIIE → TFIIH ( TFIIF/RNA Pol II
D. TFIID/TBP → TFIIA → TF11B → TFIIE → TFIIH → TFIIF/RNA Pol II
During RNA processing a(n) _____ is added to the 5′ end of the RNA.
A. 3′ untranslated region
B. a long string of adenine nucleotides
C. 5′ untranslated region
D. coding segment
E. modified guanine nucleotide
The 5′ cap consists of a modified guanine nucleotide.
A. 3′ untranslated region
B. a long string of adenine nucleotides
C. 5′ untranslated region
D. coding segment
E. modified guanine nucleotide
A poly-A tail is added to the 3′ end of the RNA.
A. snRNPs and other proteins
B. polymerases and ligases
C. introns and exons
D. the RNA transcript and protein
E. snRNPs and snurps
These are the component of spliceosomes.
A. caps
B. exons
C. snRNPs
D. tails
E. introns
A. cytoplasm
B. lysosome
C. nucleus
D. mitochondrion
E. nucleoplasm
Ribosomes, the sites of translation, are found in the cytoplasm.
