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Molecular Biology Of The Cell, Sixth Edition Bruce Alberts Test Bank
Chapter 5: Dna Replication, Repair, And Recombination
ANSWERS ARE BELOW
1 Which Of The Following Is Correct Regarding The Mutation Rate Of Genomic Dna In
Different Organisms?
A. Human Cells Have A Much Higher Mutation Rate Compared To Bacteria When The
Rate Is Normalized To A Single Round Of Replication Over The Same Length Of
Dna.
B. Mutation Rates Limit The Number Of Essential Genes In An Organism’s Genome.
C. Mutations In The Somatic Cells Cannot Be Lethal.
D. Even If The Mutation Rate Was 10 Times Higher Than Its Current Value, Germ-Cell
Stability In Humans Would Not Have Been Affected.
E. All Of The Above.
2 The Mutation Rate In Bacteria Is About 3 Nucleotide Changes Per 10 Billion Nucleotides
Per Cell Generation. Under Laboratory Conditions, Bacteria Such As Escherichia Coli Can
Divide And Double In Number About Every 40 Minutes. If A Single Escherichia Coli Cell Is
Allowed To Exponentially Divide For 10 Hours In This Manner, How Many Mutations Would
You Expect To Observe On Average In The Genome (4.5 Million Nucleotide Pairs) Of Each Of
The Resulting Bacteria Compared To The Original Cell? Assume All Mutations Are Neutral;
That Is, They Do Not Affect The Cell-Division Time.
A. Less Than 0.001
B. About 0.02
C. One Or Two
D. About 10
E. About 100
3 On Average, Errors Occur In Dna Synthesis Only Once In Every Ten Billion
Nucleotides Incorporated. Which Of The Following Does Not Contribute To This High Fidelity
Of Dna Synthesis?
A. Complementary Base-Pairing Between The Nucleotides
B. “Tightening” Of The Dna Polymerase Enzyme Around Its Active Site To Ensure
Correct Pairing Before Monomer Incorporation
C. Exonucleolytic Proofreading By The 3′-To-5′ Exonuclease Activity Of The
Enzyme To Correct Mispairing Even After Monomer Incorporation
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D. A Strand-Directed Mismatch Repair System That Detects And Resolves Mismatches
Soon After Dna Replication
E. All Of The Above Mechanisms Do Contribute To The Fidelity.
4 The Nuclear Dna Polymerases In Human Cells …
A. Polymerize About 1000 Nucleotides Per Second During Dna Replication In Vivo.
B. Are Incapable Of 3′-To-5′ Exonuclease Activity.
C. Are Capable Of 3′-To-5′ Dna Polymerase Activity.
D. Have A Single Active Site That Is Used For Both Polymerization And Editing.
E. Are Unable To Initiate Polymerization De Novo (I.E. In The Absence Of A Primer).
5 What Is The Main Source Of The Free Energy For The Mechanical Work Performed By
Dna Helicases During Dna Replication In Our Cells?
A. The Hydrogen-Bonding Energy In The Dna Double Helix
B. Thermal Energy In The Nucleus
C. Atp Hydrolysis By The Helicase
D. The Energy Of Ssb Binding To Single-Stranded Dna
E. Atp Hydrolysis By Dna Topoisomerases
6 During Dna Replication In The Cell, Dna Primase Makes Short Primers That Are
Then Extended By The Replicative Dna Polymerases. These Primers …
A. Are Made Up Of Dna.
B. Generally Have A Higher Number Of Mutations Compared To Their Neighboring Dna.
C. Are Made More Frequently In The Leading Strand Than The Lagging Strand.
D. Are Joined To The Neighboring Dna By Dna Ligase.
E. Provide A 3′-Phosphate Group For The Dna Polymerases To Extend.
7 Dna Ligases Are Used In Both Dna Replication And Repair To Seal Breaks In The Dna.
But Dna Damage Can Result In Single- Or Double-Strand Breaks That Are Not Normal Ligase
Substrates. These Need To Be Processed First Before A Ligase Can Act On Them. One Of The
Enzymes That Is Recruited To Some Of Such Breaks Is Called Pnk. It Has Two Separate
Activities On The Dna, Both Of Which Can Help Provide A Canonical Ligase Substrate. Which
Of The Following Activities Would You Expect Pnk To Have In This Context?
A. 5′ Kinase (Phosphorylation Of A Free 5′-Oh Group) And 3′ Kinase
B. 5′ Phosphatase (Dephosphorylation To Create A Free 5′-Oh Group) And 3′ Phosphatase
C. 3′ Kinase And 3′ Phosphatase
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D. 5′ Phosphatase And 3′ Kinase
E. 5′ Kinase And 3′ Phosphatase
8 Fill In The Gap In The Following Paragraph Using What You Know About The
Activities Of The Proteins Involved In Dna Replication.
“Mitochondrial Dna Replication Requires A Set Of Proteins Similar
To Those Used For The Replication Of The Nuclear Genome.
However, Mitochondria Lack A Dedicated Dna ... And Use The
Mitochondrial Rna Polymerase Instead.”
9 During Dna Replication, The Single-Strand Dna-Binding (Ssb) Proteins …
A. Are Generally Found More On The Leading Strand Than The Lagging Strand.
B. Bind Cooperatively To Single-Stranded Dna And Cover The Bases To Prevent
Base-Pairing.
C. Prevent The Folding Of The Single-Stranded Dna.
D. Bind Cooperatively To Short Hairpin Helices That Readily Form In The Single-
Stranded Dna.
E. All Of The Above.
10 This Protein Is Present At Every Replication Fork And Prevents Dna Polymerase From
Dissociating, But Does Not Impede The Rapid Movement Of The Enzyme. Which Of The
Following Is True Regarding This Protein?
A. It Self-Assembles Onto Dna At The Replication Fork.
B. It Is Assembled On Dna As Soon As Dna Polymerase Runs Into A Double-Strand
Region Of Dna.
C. Its Assembly Normally Follows The Synthesis Of A New Primer By The Dna Primase.
D. It Disassembles From Dna As Soon As Dna Polymerase Runs Into A Double-
Strand Region.
E. All Of The Above.
11 At The Replication Fork, The Template For The Lagging Strand Is Thought To Loop
Around. This Looping Would Allow The Lagging-Strand Polymerase To Move Along With The
Rest Of The Replication Fork Instead Of In The Opposite Direction. The Single-Strand Part Of
The Loop Is Bound By The Single-Strand Dna-Binding (Ssb) Proteins. As Each Okazaki
Fragment Is Synthesized Toward Completion, How Does The Size Of The Loop Change? What
About The Size Of The Ssb-Bound Part Of The Loop?
A. Increases; Increases.
Molecular Biology Of The Cell, Sixth Edition Bruce Alberts Test Bank
Chapter 5: Dna Replication, Repair, And Recombination
ANSWERS ARE BELOW
1 Which Of The Following Is Correct Regarding The Mutation Rate Of Genomic Dna In
Different Organisms?
A. Human Cells Have A Much Higher Mutation Rate Compared To Bacteria When The
Rate Is Normalized To A Single Round Of Replication Over The Same Length Of
Dna.
B. Mutation Rates Limit The Number Of Essential Genes In An Organism’s Genome.
C. Mutations In The Somatic Cells Cannot Be Lethal.
D. Even If The Mutation Rate Was 10 Times Higher Than Its Current Value, Germ-Cell
Stability In Humans Would Not Have Been Affected.
E. All Of The Above.
2 The Mutation Rate In Bacteria Is About 3 Nucleotide Changes Per 10 Billion Nucleotides
Per Cell Generation. Under Laboratory Conditions, Bacteria Such As Escherichia Coli Can
Divide And Double In Number About Every 40 Minutes. If A Single Escherichia Coli Cell Is
Allowed To Exponentially Divide For 10 Hours In This Manner, How Many Mutations Would
You Expect To Observe On Average In The Genome (4.5 Million Nucleotide Pairs) Of Each Of
The Resulting Bacteria Compared To The Original Cell? Assume All Mutations Are Neutral;
That Is, They Do Not Affect The Cell-Division Time.
A. Less Than 0.001
B. About 0.02
C. One Or Two
D. About 10
E. About 100
3 On Average, Errors Occur In Dna Synthesis Only Once In Every Ten Billion
Nucleotides Incorporated. Which Of The Following Does Not Contribute To This High Fidelity
Of Dna Synthesis?
A. Complementary Base-Pairing Between The Nucleotides
B. “Tightening” Of The Dna Polymerase Enzyme Around Its Active Site To Ensure
Correct Pairing Before Monomer Incorporation
C. Exonucleolytic Proofreading By The 3′-To-5′ Exonuclease Activity Of The
Enzyme To Correct Mispairing Even After Monomer Incorporation
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D. A Strand-Directed Mismatch Repair System That Detects And Resolves Mismatches
Soon After Dna Replication
E. All Of The Above Mechanisms Do Contribute To The Fidelity.
4 The Nuclear Dna Polymerases In Human Cells …
A. Polymerize About 1000 Nucleotides Per Second During Dna Replication In Vivo.
B. Are Incapable Of 3′-To-5′ Exonuclease Activity.
C. Are Capable Of 3′-To-5′ Dna Polymerase Activity.
D. Have A Single Active Site That Is Used For Both Polymerization And Editing.
E. Are Unable To Initiate Polymerization De Novo (I.E. In The Absence Of A Primer).
5 What Is The Main Source Of The Free Energy For The Mechanical Work Performed By
Dna Helicases During Dna Replication In Our Cells?
A. The Hydrogen-Bonding Energy In The Dna Double Helix
B. Thermal Energy In The Nucleus
C. Atp Hydrolysis By The Helicase
D. The Energy Of Ssb Binding To Single-Stranded Dna
E. Atp Hydrolysis By Dna Topoisomerases
6 During Dna Replication In The Cell, Dna Primase Makes Short Primers That Are
Then Extended By The Replicative Dna Polymerases. These Primers …
A. Are Made Up Of Dna.
B. Generally Have A Higher Number Of Mutations Compared To Their Neighboring Dna.
C. Are Made More Frequently In The Leading Strand Than The Lagging Strand.
D. Are Joined To The Neighboring Dna By Dna Ligase.
E. Provide A 3′-Phosphate Group For The Dna Polymerases To Extend.
7 Dna Ligases Are Used In Both Dna Replication And Repair To Seal Breaks In The Dna.
But Dna Damage Can Result In Single- Or Double-Strand Breaks That Are Not Normal Ligase
Substrates. These Need To Be Processed First Before A Ligase Can Act On Them. One Of The
Enzymes That Is Recruited To Some Of Such Breaks Is Called Pnk. It Has Two Separate
Activities On The Dna, Both Of Which Can Help Provide A Canonical Ligase Substrate. Which
Of The Following Activities Would You Expect Pnk To Have In This Context?
A. 5′ Kinase (Phosphorylation Of A Free 5′-Oh Group) And 3′ Kinase
B. 5′ Phosphatase (Dephosphorylation To Create A Free 5′-Oh Group) And 3′ Phosphatase
C. 3′ Kinase And 3′ Phosphatase
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D. 5′ Phosphatase And 3′ Kinase
E. 5′ Kinase And 3′ Phosphatase
8 Fill In The Gap In The Following Paragraph Using What You Know About The
Activities Of The Proteins Involved In Dna Replication.
“Mitochondrial Dna Replication Requires A Set Of Proteins Similar
To Those Used For The Replication Of The Nuclear Genome.
However, Mitochondria Lack A Dedicated Dna ... And Use The
Mitochondrial Rna Polymerase Instead.”
9 During Dna Replication, The Single-Strand Dna-Binding (Ssb) Proteins …
A. Are Generally Found More On The Leading Strand Than The Lagging Strand.
B. Bind Cooperatively To Single-Stranded Dna And Cover The Bases To Prevent
Base-Pairing.
C. Prevent The Folding Of The Single-Stranded Dna.
D. Bind Cooperatively To Short Hairpin Helices That Readily Form In The Single-
Stranded Dna.
E. All Of The Above.
10 This Protein Is Present At Every Replication Fork And Prevents Dna Polymerase From
Dissociating, But Does Not Impede The Rapid Movement Of The Enzyme. Which Of The
Following Is True Regarding This Protein?
A. It Self-Assembles Onto Dna At The Replication Fork.
B. It Is Assembled On Dna As Soon As Dna Polymerase Runs Into A Double-Strand
Region Of Dna.
C. Its Assembly Normally Follows The Synthesis Of A New Primer By The Dna Primase.
D. It Disassembles From Dna As Soon As Dna Polymerase Runs Into A Double-
Strand Region.
E. All Of The Above.
11 At The Replication Fork, The Template For The Lagging Strand Is Thought To Loop
Around. This Looping Would Allow The Lagging-Strand Polymerase To Move Along With The
Rest Of The Replication Fork Instead Of In The Opposite Direction. The Single-Strand Part Of
The Loop Is Bound By The Single-Strand Dna-Binding (Ssb) Proteins. As Each Okazaki
Fragment Is Synthesized Toward Completion, How Does The Size Of The Loop Change? What
About The Size Of The Ssb-Bound Part Of The Loop?
A. Increases; Increases.
