Question 1

Which event does not occur during DNA replication?
A) Unwinding of the parent double helix
B) Formation of short pieces that are connected by DNA ligase
C) Complementary base pairing
D) Use of a primer
E) Polymerization in the 3'-to-5' direction

Accepted Answer

DNA polymerization occurs in the 5' to 3' direction, not 3' to 5'.

Question 2

A research laboratory uses a cancer cell line that has undergone thousands of cell cycle divisions in the laboratory without any change in the length of its chromosomes.The cancer cell line is therefore likely to express
A) high levels of RNA polymerase.
B) very low levels of telomerase.
C) high levels of telomerase.
D) DNA polymerases with high fidelity.
E) high levels of ligase activity.

Accepted Answer

Telomerase is an enzyme that adds repetitive DNA sequences (known as telomeres) to the ends of chromosomes in order to prevent their deterioration and loss of genetic information during cell division. Normal body cells have limited telomerase activity, which leads to gradual telomere shortening and eventual cell death. However, cancer cells often have increased telomerase activity, which enables them to maintain their telomere length and undergo unlimited cell divisions. Therefore, it is likely that the cancer cell line in the research laboratory expresses high levels of telomerase.

Question 3

Individual cells do not survive for the entire lifetime of an organism because
A) the enzyme telomerase is readily destroyed by the environment,resulting in cell death.
B) DNA replication is subject to errors that cause cell death.
C) Okazaki fragments disrupt protein synthesis,resulting in cell death.
D) the repeating telomeric sequence of TTAGGG interferes with normal DNA replication and leads to cell death.
E) the removal of the RNA primer following DNA replication leads to a shortening of the chromosome and eventual cell death.

Accepted Answer

The removal of the RNA primer during DNA replication results in the shortening of chromosomes because the DNA polymerase cannot fill in the gap left by the primer at the end of the lagging strand. This leads to progressive shortening of telomeres, eventually causing cell death when they become too short.

Question 4

The primer used for DNA replication
A) is a short strand of RNA added to the 5'end of the template strand.
B) is needed only once on a leading strand.
C) remains on the DNA after replication.
D) ensures that there will be a free 5' end to which nucleotides can be added.
E) is added to only one of the two template strands.

Accepted Answer

The answer of The primer used for DNA replication
A) is...

Question 5

The stem cells in your intestinal walls divide frequently.Therefore,these cells are likely to
A) have high levels of telomerase.
B) have very low levels of telomerase.
C) undergo the polymerase chain reaction.
D) lack DNA polymerase.
E) lack Okazaki fragments.

Accepted Answer

Stem cells in the intestinal walls divide frequently in order to constantly regenerate the lining of the intestines. Division of cells leads to the shortening of telomeres, the protective ends of chromosomes. Therefore, in order to maintain the long-term viability of these cells, they are likely to have high levels of telomerase, which is an enzyme that adds telomeric DNA to the ends of chromosomes to counteract telomere shortening.

Question 6

Which statement about a eukaryotic DNA replication primer is true?
A) It is a short strand of RNA added to the 3'end of the leading strand.
B) It is needed only once on a lagging strand.
C) It remains on the DNA after replication.
D) It ensures that there will be a free 5' end to which nucleotides can be added.
E) It is added to only one of the two template strands.

Accepted Answer

A eukaryotic DNA replication primer is a short strand of RNA that is added to the 3' end of the leading strand. This RNA primer provides a free 3' OH group to which DNA polymerase can add nucleotides. Once the RNA primer has been used as a template for DNA synthesis, it is removed by RNase H and replaced with DNA nucleotides. The primer is only added to the leading strand and is required at the beginning of each Okazaki fragment on the lagging strand. It does not remain on the DNA after replication is complete.

Question 7

In eukaryotes,the error rate of incorrect bases following proofreading and mismatch repair is approximately one in _______ per cell cycle. A) 10 B) 10^-³ C) 10^-⁵ D) 10^-¹⁰ E) 10^-¹⁵

Accepted Answer

The error rate of DNA replication in eukaryotes after proofreading and mismatch repair is approximately one in 10^-¹⁰ per cell cycle.

Question 8

What prevents the DNA repair system from "repairing" telomeres?
A) Telomerase is bound to telomeres,and thus blocks the repair system from binding to telomeres.
B) Telomerase catalyzes reactions that interfere with the repair system.
C) DNA polymerase blocks the repair system from accessing the telomere DNA.
D) Telomeres are at the end of the chromosome,and DNA is replicated in only one direction.
E) Protective proteins bind to telomeres,and therefore the repair system does not recognize telomeres as breaks.

Accepted Answer

Protective proteins bind to telomeres and form a protective cap, which prevents the DNA repair system from recognizing telomeres as breaks and initiating repair processes. This is important for maintaining telomere length and preventing fusion with neighboring chromosomes. Telomerase, on the other hand, adds new telomeric repeats to the end of chromosomes, counteracting the loss of telomeres during DNA replication.

Question 9

Which statement about Okazaki fragments is true?
A) They occur because DNA polymerase operates in only one direction along a strand of DNA.
B) They act as a primer that initiates DNA replication.
C) If they did not exist,the ends of chromosomes would get shorter with every replication.
D) It they did not exist,bases would pair with their complementary bases.
E) They reduce the mutation rate during DNA replication.

Accepted Answer

Okazaki fragments are short, newly synthesized DNA fragments that are created on the lagging strand of DNA during DNA replication. They are necessary because DNA polymerase can only add new nucleotides in the 5' to 3' direction, so as the replication fork moves, the leading strand is synthesized continuously, but the lagging strand is synthesized in short fragments that are later joined together by DNA ligase.

Question 10

The role of DNA ligase in DNA replication is to
A) add more nucleotides to the growing strand,one at a time.
B) open up the two DNA strands to expose template strands.
C) ligate base to sugar to phosphate in a nucleotide.
D) bond Okazaki fragments to one another.
E) remove incorrectly paired bases.

Accepted Answer

DNA ligase is responsible for joining Okazaki fragments that were created on the lagging strand during DNA replication. It does not add nucleotides to the growing strand or open up the DNA strands. Additionally, DNA ligase does not ligate base to sugar to phosphate in a nucleotide and does not remove incorrectly paired bases.

Question 11

What local effect would an RNA synthesis inhibitor have on DNA replication?
A) Primase would not be able to add bases to the DNA.
B) Primase would not be able to use DNA as a template.
C) Primase would be blocked from joining the holoenzyme complex.
D) Primase would not be able to provide primers for DNA polymerases.
E) There would be no effect on DNA replication.

Accepted Answer

RNA synthesis is necessary for the synthesis of primers, which are required for DNA polymerase to begin replicating the DNA strand. If RNA synthesis is inhibited, primase would not be able to produce primers, thereby halting DNA replication. Choices A, B, and C are all related to the function of primase, but choice D directly addresses the impact on DNA replication. Choice E is incorrect because inhibition of RNA synthesis would have a direct effect on DNA replication.

Question 12

Why is RNA incorporated into the DNA molecule during DNA replication?
A) DNA polymerases can only add on to an existing strand.
B) RNA primase is able to use DNA as a template.
C) RNA primase must be incorporated into the holoenzyme complex.
D) DNA polymerase first synthesizes RNA.
E) RNA serves as the template for DNA synthesis.

Accepted Answer

DNA polymerases require a primer with a free 3'-OH group to initiate DNA synthesis, and RNA primers provide this starting point.

Question 13

Fragments like those now called Okazaki fragments might have been hypothesized even before they were discovered by Reiji Okazaki because
A) DNA replicates in the 3'-to-5' direction.
B) single-stranded 5'-to-3' DNA appears behind DNA polymerase.
C) DNA nucleotides are added to the 5' end of the primer on the lagging strand.
D) RNA primase places short RNA primer sequences along the DNA molecule.
E) DNA polymerase I can connect short segments.

Accepted Answer

The observation of single-stranded DNA appearing behind DNA polymerase during replication would suggest the idea of discontinuous synthesis, and therefore the possible existence of Okazaki fragments.

Question 14

The molecules that function to replicate DNA in the cell are
A) DNA nucleoside triphosphates.
B) DNA polymerases.
C) nucleoside polymerases.
D) DNAses.
E) ribonucleases.

Accepted Answer

DNA polymerases are enzymes responsible for DNA replication. They catalyze the addition of nucleotides to a growing DNA chain, using a pre-existing strand as a template. DNA nucleoside triphosphates are the building blocks of DNA, but they are not responsible for the replication process itself. Nucleoside polymerases, DNAses, and ribonucleases are not directly involved in DNA replication.

Question 15

In what way does DNA replication differ in eukaryotes versus prokaryotes?
A) In eukaryotes,synthesis of the new DNA strand is from 3' to 5',whereas in prokaryotes it is from 5' to 3'.
B) In eukaryotes,synthesis of the new DNA strand is from 5' to 3',whereas in prokaryotes it is from 3' to 5'.
C) There are many origins of replication in each eukaryotic chromosome and only one in bacterial DNA.
D) In eukaryotes,synthesis of the new DNA strand is from 5' to 3',whereas in prokaryotes it is random.
E) Okazaki fragments are produced in eukaryotic DNA replication but not in prokaryotic DNA replication.

Accepted Answer

Eukaryotic chromosomes have multiple origins of replication to efficiently replicate their larger genomes, while prokaryotic DNA typically has a single origin of replication.

Question 16

In DNA replication,the processive nature of DNA polymerase
A) increases the number of nucleotides that can be polymerized per enzymatic cycle.
B) holds open the two strands of the DNA molecule for access to the bonds.
C) allows it to jump from one DNA strand to another.
D) temporarily holds the nucleotides together until phosphodiester bonds can form.
E) unwinds the double helix to allow the DNA polymerase to bind.

Accepted Answer

The processive nature of DNA polymerase means that it can add multiple nucleotides in a row without falling off the template strand. This increases the speed of replication and the number of nucleotides that can be added per enzymatic cycle.

Question 17

A deoxyribonucleotide is a
A) deoxyribose plus a nitrogenous base.
B) sugar and a phosphate.
C) nitrogenous base bonded at the 5' end to a sugar-phosphate backbone.
D) ribose plus a nitrogenous base.
E) deoxyribose plus a nitrogenous base and a phosphate group.

Accepted Answer

A deoxyribonucleotide is made up of three components: a deoxyribose sugar, a nitrogenous base, and a phosphate group. Therefore, the best choice is E which includes all three components. A is incorrect because it only includes a sugar and a nitrogenous base, while B only includes a sugar and a phosphate group. C is describing the general structure of a DNA molecule, not a deoxyribonucleotide specifically. D is incorrect because it includes ribose sugar instead of deoxyribose sugar.

Question 18

The enzyme DNA ligase is required continuously during DNA replication because
A) fragments of the leading strand must be joined together.
B) fragments of the lagging strand must be joined together.
C) the parental strands must be joined back together.
D) 3'-deoxynucleoside triphosphates must be converted to 5'-deoxynucleoside triphosphates.
E) the complex of proteins that work together at the replication fork must be prevented from falling apart.

Accepted Answer

DNA ligase is responsible for joining together the fragments of the lagging strand during DNA replication, as it is synthesized in short pieces known as Okazaki fragments. The fragments of the leading strand do not require ligation, as they are synthesized continuously in the same direction as DNA unwinding. Therefore, B is the correct answer.

Question 19

DNA polymerase lengthens a polynucleotide strand by
A) building short DNA fragments and linking them together.
B) adding lost DNA sequences to the 3' end.
C) linking purines with pyrimidines.
D) threading the existing DNA through a replication complex.
E) covalently linking new nucleotides to a previously existing strand.

Accepted Answer

DNA polymerase lengthens a polynucleotide strand by covalently linking new nucleotides to a previously existing strand. This is achieved by base pairing between complementary nucleotides and formation of phosphodiester bonds between the 3' hydroxyl group of the existing nucleotide and the 5' phosphate group of the incoming nucleotide. This process continues until the entire length of the strand is replicated. Choices A, B, C, and D do not accurately describe the mechanism of DNA polymerase during replication.

Question 20

In eukaryotes,Okazaki fragments are about _______ base pairs long.
A) 5-10
B) 100-200
C) 500-1,000
D) 1,000-2,000
E) 10,000-20,000

Accepted Answer

Okazaki fragments in eukaryotes are about 100-200 base pairs long. This is shorter than the Okazaki fragments in prokaryotes which can be up to 1000 base pairs long.

Quiz 9: DNA and Its Role in Heredity

Which event does not occur during DNA replication?

A research laboratory uses a cancer cell line that has undergone thousands of cell cycle divisions in the laboratory without any change in the length of its chromosomes.The cancer cell line is therefore likely to express

Individual cells do not survive for the entire lifetime of an organism because

The primer used for DNA replication

The stem cells in your intestinal walls divide frequently.Therefore,these cells are likely to

Which statement about a eukaryotic DNA replication primer is true?

In eukaryotes,the error rate of incorrect bases following proofreading and mismatch repair is approximately one in _______ per cell cycle.

What prevents the DNA repair system from "repairing" telomeres?

Which statement about Okazaki fragments is true?

The role of DNA ligase in DNA replication is to

What local effect would an RNA synthesis inhibitor have on DNA replication?

Why is RNA incorporated into the DNA molecule during DNA replication?

Fragments like those now called Okazaki fragments might have been hypothesized even before they were discovered by Reiji Okazaki because

The molecules that function to replicate DNA in the cell are

In what way does DNA replication differ in eukaryotes versus prokaryotes?

In DNA replication,the processive nature of DNA polymerase

A deoxyribonucleotide is a

The enzyme DNA ligase is required continuously during DNA replication because

DNA polymerase lengthens a polynucleotide strand by

In eukaryotes,Okazaki fragments are about _______ base pairs long.