Chapter 18 Mastering Bio Q’s & Answers

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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(n) ______ is a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway
Operon
The ________ is/are arranged sequentially after the promoter.
Genes of an operon
A(n) _______ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.
Promoter
A(n) _______ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes
Regulatory Gene
Regulatory proteins bind to the _________ to control expression of the operon.
Operator
A(n) __________ is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.
Repressor
A(n) _____ is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on
Inducer
rank the events of transcription initiation that occur before the elongation phase begins:
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
F, C, B, D, E, A
What is the process called that converts the genetic information stored in DNA to an RNA copy?
A. Replication
B. Transcription
C. Translocation
D. Translation
B. Transcription
DNA is transcribed to give an RNA copy.
DNA does not store the information to synthesize which of the following?
A. Organelles
B. DNA
C. Messenger RNA
D. Proteins
A. Organelles
Synthesis of organelles is not directly coded in the DNA.
Transcription begins at a promoter. What is a promoter?
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
C. A site in DNA that recruits the RNA Polymerase
This is the site where the RNA polymerase must bind to initiate transcription.
Which of the following statements best describes the promoter of a protein-coding gene?
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.
C. The promoter is a nontranscribed region of a gene.
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.
What determines which base is to be added to an RNA strand during transcription?
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
C. Base pairing between the DNA template strand and the RNA nucleotides
Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?
A. Identical
B. Covalently bound
C. Complementary
D. Permanently base-paired
C. Complementary
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.
What happens to RNA polymerase II after it has completed transcription of a gene?
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.
A. It is free to bind to another promoter and begin transcription.
The enzyme is free to transcribe other genes in the cell.
Which of the following best characterizes the interactions between σ factor and a typical gene promoter in E. coli?
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.
A
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.
To what does an “aminoacyl-tRNA” refer?
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.

True or false? A codon is a group of three bases that can specify more than one amino acid.
False
A codon is a group of three bases that can specify only one amino acid.
Which of the following statements about mutations is false?
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.
D. A knock-out mutation refers to the loss of a protein’s function but not necessarily to its complete absence.
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?
A. Both addition and deletion.
B. None.
C. Deletion.
D. Addition.
C. Deletion
The original sequence has lost the base C.
Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)?
A. One addition and two deletion mutations.
B. One addition and one deletion mutation.
C. One addition mutation.
D. One deletion mutation.
B.
This combination results in no net change in the number of bases, so the reading frame would eventually be restored.
If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein?
A. One.
B. None.
C. Two.
D. Three.
C.
The second and third codons in the new sequence are different from the original codons.
If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?
A. An addition mutation and a deletion mutation.
B. None.
C. An addition mutation
D. A deletion mutation.
A.
If the mutations occur within the same codon, only that codon (amino acid) will be altered
Name the two amino acids (using three letter abbreviations) that do not have codon degeneracy.
Met, Trp
In prokaryotes, the methionine that initiates the formation of a polypeptide chain differs from subsequently added methionines in that _______.
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
C
This modification is not present on methionine residues added during elongation.
Translation is directly dependent on all of the following associations except _______.
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
A
Transcription, not translation, is dependent on this association.
Which of the following best describes the first step in the formation of the translation initiation complex?
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
D
Once elongation is underway, tRNAs involved in the process occupy a series of sites on the complexed ribosome. The occupation of sites occurs in the following order.
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
B
When a peptide bond is formed between two amino acids, one is attached to the tRNA occupying the P site and the other _______.
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
C
Which of the following statements concerning peptide bond formation is correct?
A. It requires GTP.
B. It is catalyzed by an enzymatic protein.
C. It is catalyzed by peptidyl transferase.
D. It uses water.
C
Which of the following statements best defines the term operon?
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.
C
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?
A. DNA polymerase
B. DNA ligase
C. RNA polymerase
D. A nucleotide
C
RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.
What is allosteric regulation?
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.
B
Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators.
Under which conditions are the lac structural genes expressed most efficiently?
A. No glucose, high lactose
B. No glucose, no lactose
C. High glucose, no lactose
D. High glucose, high lactose
A
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.
What happens to the expression of the lacI gene if lactose is not available in the cell?
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.
A
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.
What is the function of the lacZ gene?
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.
C
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?
A. b-galactosidase
B. Galactoside permease
C. Adenylyl cyclase
D. ATP synthase
C
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.
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. 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
A
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?
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.
A
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.
A. True
B. False
A
When the repressor binds to the operator, RNA polymerase cannot transcribe the structural genes.
In a genetic screen, researchers isolated mutants of E. coli that constitutively expressed the genes from the araBAD operon. Describe what constitutive expression means in terms of the araBAD operon.
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.
C
In prokaryotes, when can basal level (constitutive) expression of a gene occur?
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
D
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.
Which of the following describes the correct stepwise assembly (in vitro) of the eukaryotic RNA polymerase II preinitiation complex?
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
A

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

E
The 5′ cap consists of a modified guanine nucleotide.
During RNA processing a(n) _____ is added to the 3′ 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
B
A poly-A tail is added to the 3′ end of the RNA.
Spliceosomes are composed of _____.
A. snRNPs and other proteins
B. polymerases and ligases
C. introns and exons
D. the RNA transcript and protein
E. snRNPs and snurps
A
These are the component of spliceosomes.
The RNA segments joined to one another by spliceosomes are _____.
A. caps
B. exons
C. snRNPs
D. tails
E. introns
B
Translation occurs in the _____.
A. cytoplasm
B. lysosome
C. nucleus
D. mitochondrion
E. nucleoplasm
A
Ribosomes, the sites of translation, are found in the cytoplasm.

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