Question 1

It takes about the same amount of time for eukaryotic chromosomes to be replicated in vivo as it does for E.coli.Why is this true?

Accepted Answer

A) Eukaryotes have multiple origins of replication;E.coli has one unique origin. 
B) Most chromosomes are approximately the same size. 
C) Eukaryotic replication occurs at a faster rate,enabling replication of the larger chromosomes in about the same amount of time. 
D) The replication of DNA in eukaryotes is faster due to a quicker,more accurate repair of mismatches. 
A) Eukaryotes have multiple origins of replication;E.coli has one unique origin. 
B) Most chromosomes are approximately the same size. 
C) Eukaryotic replication occurs at a faster rate,enabling replication of the larger chromosomes in about the same amount of time. 
D) The replication of DNA in eukaryotes is faster due to a quicker,more accurate repair of mismatches.

Question 2

The 3' → 5' exonuclease activity of E.coli DNA polymerase III accounts for the ________ of polymerization.

Accepted Answer

A) low error rate 
B) high speed 
C) directionality 
D) All of the above 
A) low error rate 
B) high speed 
C) directionality 
D) All of the above

Question 3

What distinguishes direct repair from other DNA repair mechanisms?

Accepted Answer

A) Direct repair does not require the breaking of any bonds in the DNA phosphodiester backbone. 
B) Direct repair proteins do not require activation by light or other chemicals. 
C) Direct repair systems activate the proofreading activity of DNA polymerase. 
D) Direct repair systems remove and replace single defective nucleotides. 
A) Direct repair does not require the breaking of any bonds in the DNA phosphodiester backbone. 
B) Direct repair proteins do not require activation by light or other chemicals. 
C) Direct repair systems activate the proofreading activity of DNA polymerase. 
D) Direct repair systems remove and replace single defective nucleotides.

Question 4

Which is not part of the replisome?

Accepted Answer

A) Helicase DnaB. 
B) The primosome. 
C) Gyrase. 
D) Single-stranded binding protein. 
A) Helicase DnaB. 
B) The primosome. 
C) Gyrase. 
D) Single-stranded binding protein.

Question 5

What is the function of single-strand binding protein (SSB)(helix stabilizing protein)?

Accepted Answer

A) It stabilizes nicks on the lagging strand during replication until DNA ligase seals the nick. 
B) It recognizes thymine dimers in DNA,which make the DNA single-stranded,and serves as a signal for the activation of repair proteins. 
C) It stabilizes many forms of RNA which are single-stranded. 
D) During replication it binds to single-stranded regions of the lagging strand and prevents it from folding back on itself into double-helical regions. 
A) It stabilizes nicks on the lagging strand during replication until DNA ligase seals the nick. 
B) It recognizes thymine dimers in DNA,which make the DNA single-stranded,and serves as a signal for the activation of repair proteins. 
C) It stabilizes many forms of RNA which are single-stranded. 
D) During replication it binds to single-stranded regions of the lagging strand and prevents it from folding back on itself into double-helical regions.

Question 6

Why does E.coli need both DNA polymerase III and DNA polymerase I?

Accepted Answer

A) DNA polymerase III lacks the 5' → 3' exonuclease activity needed to remove RNA primers. 
B) Each polymerase is specific for only one strand of DNA.DNA polymerase III acts only on the leading strand,and DNA polymerase I acts only on the lagging strand. 
C) DNA polymerase I is needed to join the Okazaki fragments. 
D) The DNA replication is bidirectional;one polymerase is used for each direction. 
E) Only DNA polymerase I has proofreading ability. 
A) DNA polymerase III lacks the 5' → 3' exonuclease activity needed to remove RNA primers. 
B) Each polymerase is specific for only one strand of DNA.DNA polymerase III acts only on the leading strand,and DNA polymerase I acts only on the lagging strand. 
C) DNA polymerase I is needed to join the Okazaki fragments. 
D) The DNA replication is bidirectional;one polymerase is used for each direction. 
E) Only DNA polymerase I has proofreading ability.

Question 7

Meselson and Stahl's experiments involved growing E.coli on a medium containing 15N (heavy nitrogen)which increased the density of the bacterial DNA.Cells were then grown on a medium containing only 14N.DNA samples were obtained for analysis after one,two and three rounds of replication (generations)and centrifuged on a density gradient.The double-helical DNA forms bands in the gradient depending on its density.How many bands did Meselson and Stahl see after two generation of cells were grown on the 14N medium?

Accepted Answer

A) One with DNA containing both 15N and 14N. 
B) Two,one with DNA containing only 15N and one with DNA containing only 14N. 
C) Two,one with DNA containing both 15N and 14N and one with DNA containing only 14N. 
D) Three,one with DNA containing only 15N,one with DNA containing both 15N and 14N and one with DNA containing only 14N. 
A) One with DNA containing both 15N and 14N. 
B) Two,one with DNA containing only 15N and one with DNA containing only 14N. 
C) Two,one with DNA containing both 15N and 14N and one with DNA containing only 14N. 
D) Three,one with DNA containing only 15N,one with DNA containing both 15N and 14N and one with DNA containing only 14N.

Question 8

During the elongation stage

Accepted Answer

A) replication proteins assemble at the DNA replication site. 
B) DNA is replicated semiconservatively. 
C) the protein machine disassembles. 
D) replication ends. 
A) replication proteins assemble at the DNA replication site. 
B) DNA is replicated semiconservatively. 
C) the protein machine disassembles. 
D) replication ends.

Question 9

A short primer is added to the DNA polymerase reaction mix for Sanger DNA sequencing that has a 5' free hydroxyl to which new nucleotides can be added.

Accepted Answer

A) True 
 B)False

Question 10

DNA is the only cell macromolecule that can be repaired.

Accepted Answer

A) True 
 B)False

Question 11

The protein machine that carries out DNA replication is called ________.

Accepted Answer

A) DNA polymerase 
B) the replication fork 
C) the Klenow fragment 
D) the replisome 
A) DNA polymerase 
B) the replication fork 
C) the Klenow fragment 
D) the replisome

Question 12

What is a Klenow fragment?

Accepted Answer

A) A fragment of DNA polymerase I that lacks 5' → 3' exonuclease activity. 
B) A topoisomerase responsible for unwinding DNA at the replication fork. 
C) A portion of the replisome responsible for RNA primer synthesis. 
D) Short stretches of DNA formed during polymerization of the lagging strand. 
A) A fragment of DNA polymerase I that lacks 5' → 3' exonuclease activity. 
B) A topoisomerase responsible for unwinding DNA at the replication fork. 
C) A portion of the replisome responsible for RNA primer synthesis. 
D) Short stretches of DNA formed during polymerization of the lagging strand.

Question 13

The sequence of proteins used in bacterial recombination is:

Accepted Answer

A) RuvC → RuvB → RecA → RecBCD 
B) RecBCD → RecA → RuvAB → RuvC 
C) RecA → RecBCD → RuvAB → RuvC 
D) RuvAB → RuvC → RecBCD → RecA 
A) RuvC → RuvB → RecA → RecBCD 
B) RecBCD → RecA → RuvAB → RuvC 
C) RecA → RecBCD → RuvAB → RuvC 
D) RuvAB → RuvC → RecBCD → RecA

Question 14

In the Sanger method for DNA sequencing,the gels are read from bottom to top,since the smallest fragments travel farthest in the sequencing gel.

Accepted Answer

A) True 
 B)False

Question 15

How are the BRCA proteins and their genes implicated in breast cancer?

Accepted Answer

A) The BRCA proteins damage DNA by generating double-stranded breaks which can lead to cancer. 
B) Cells become more susceptible to damage if the genes for these proteins are damaged. 
C) BRCA proteins inhibit excision repair mechanisms. 
D) BRCA proteins initiate recombination between non-homologous DNA sequences. 
A) The BRCA proteins damage DNA by generating double-stranded breaks which can lead to cancer. 
B) Cells become more susceptible to damage if the genes for these proteins are damaged. 
C) BRCA proteins inhibit excision repair mechanisms. 
D) BRCA proteins initiate recombination between non-homologous DNA sequences.

Question 16

On average about twenty errors are made during each replication of the human genome.

Accepted Answer

A) True 
 B)False

Question 17

Why is DNA damage in skin cells from exposure to excessive UV light not completely reversed by photoreactivation?

Accepted Answer

A) DNA photolyase in humans is activated only under conditions of heat shock. 
B) Humans lack a photoreactivation repair mechanism. 
C) The presence of histones greatly slows photoreactivation,thus humans depends primarily on other forms of DNA repair. 
D) Photoreactivation is specific for the removal of thymine dimers.Thymine dimers do not form in human DNA. 
A) DNA photolyase in humans is activated only under conditions of heat shock. 
B) Humans lack a photoreactivation repair mechanism. 
C) The presence of histones greatly slows photoreactivation,thus humans depends primarily on other forms of DNA repair. 
D) Photoreactivation is specific for the removal of thymine dimers.Thymine dimers do not form in human DNA.

Question 18

In packaging the eukaryotic DNA into nucleosomes,it is thought that the requirement for ________ and their synthesis is a cause of the slower rate of movement of the replication fork.

Accepted Answer

A) Okazaki fragments 
B) larger DNA molecules 
C) increase number of accessory proteins 
D) histone proteins 
E) lagging strands 
A) Okazaki fragments 
B) larger DNA molecules 
C) increase number of accessory proteins 
D) histone proteins 
E) lagging strands

Question 19

The processivity of E.coli DNA polymerase III holoenzyme accounts for all of the following except

Accepted Answer

A) the relatively small number of enzymes needed to replicate the entire chromosome. 
B) the directionality of polymerization. 
C) the rapid rate of polymerization. 
D) the ability of a single holoenzyme to add many nucleotides to a growing DNA chain. 
A) the relatively small number of enzymes needed to replicate the entire chromosome. 
B) the directionality of polymerization. 
C) the rapid rate of polymerization. 
D) the ability of a single holoenzyme to add many nucleotides to a growing DNA chain.

Question 20

The chromosome of the fruit fly (D.melanogaster)is about twice as large as the E.coli chromosome.

Accepted Answer

A) True 
 B)False

Exam 20: DNA Replication, repair, and Recombination

It takes about the same amount of time for eukaryotic chromosomes to be replicated in vivo as it does for E.coli.Why is this true?

The 3' → 5' exonuclease activity of E.coli DNA polymerase III accounts for the ________ of polymerization.

What distinguishes direct repair from other DNA repair mechanisms?

Which is not part of the replisome?

What is the function of single-strand binding protein (SSB)(helix stabilizing protein)?

Why does E.coli need both DNA polymerase III and DNA polymerase I?

During the elongation stage

A short primer is added to the DNA polymerase reaction mix for Sanger DNA sequencing that has a 5' free hydroxyl to which new nucleotides can be added.

DNA is the only cell macromolecule that can be repaired.

The protein machine that carries out DNA replication is called ________.

What is a Klenow fragment?

The sequence of proteins used in bacterial recombination is:

In the Sanger method for DNA sequencing,the gels are read from bottom to top,since the smallest fragments travel farthest in the sequencing gel.

How are the BRCA proteins and their genes implicated in breast cancer?

On average about twenty errors are made during each replication of the human genome.

Why is DNA damage in skin cells from exposure to excessive UV light not completely reversed by photoreactivation?

In packaging the eukaryotic DNA into nucleosomes,it is thought that the requirement for ________ and their synthesis is a cause of the slower rate of movement of the replication fork.

The processivity of E.coli DNA polymerase III holoenzyme accounts for all of the following except

The chromosome of the fruit fly (D.melanogaster)is about twice as large as the E.coli chromosome.

Introduction to Biochemistry

Water

Amino Acids and the Primary Structures of Proteins

Proteins: Three-Dimensional Structure and Function

Properties of Enzymes

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Atp Synthesis

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

Transcription and RNA Processing

Protein Synthesis

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