Question 1

Which statement about Okazaki fragments is true?

Accepted Answer

Okazaki fragments are short, discontinuous pieces of DNA that are synthesized on the lagging strand during DNA replication. They are necessary because DNA synthesis can only proceed in the 5' to 3' direction, which causes problems for the replication of the lagging strand, which is oriented 3' to 5' with respect to the replication fork. Therefore, DNA must be synthesized in short, Okazaki fragments that are later joined together by DNA ligase to form a continuous strand.

Question 2

An individual inherits two defective copies of the MLH1 gene, a protein involved in mismatch repair of DNA during its replication.What do you predict will be the consequences of deficient mismatch repair upon DNA replication?

Accepted Answer

Deficient mismatch repair will result in a higher frequency of mutations becoming fixed in the newly synthesized strand because the replication complex will no longer recognize and correct mismatches. This can lead to accumulation of mutations and eventually result in genetic diseases such as cancer.

Question 3

The enzyme that restores the phosphodiester linkage between adjacent fragments in the lagging strand during DNA replication is

Accepted Answer

The enzyme that restores the phosphodiester linkage between adjacent fragments in the lagging strand during DNA replication is DNA ligase. It joins the Okazaki fragments together by forming a phosphodiester bond between the adjacent nucleotides.

Question 4

Which DNA repair system or mechanism acts as the second line of defense against mutational error that occurs as the result of DNA replication?

Accepted Answer

Mismatch repair is the DNA repair system or mechanism that acts as the second line of defense against mutational errors that occur as a result of DNA replication. This system recognizes and repairs mismatched base pairs that were not corrected by proofreading during DNA replication. Excision repair is another type of DNA repair mechanism that repairs DNA damage caused by environmental factors such as UV radiation, while proofreading is a process that occurs during DNA replication to correct errors made by DNA polymerase. Telomerase is an enzyme that adds repetitive DNA sequences to the ends of chromosomes to prevent degradation, and ligation is the process of linking two DNA strands together.

Question 5

What joins Okazaki fragments together?

Accepted Answer

Okazaki fragments are short, discontinuous sequences of DNA that are generated during DNA replication on the lagging strand. These fragments are joined together by DNA ligase, which forms a phosphodiester bond between the 3' hydroxyl group of one fragment and the 5' phosphate group of the adjacent fragment, creating a continuous strand of DNA. DNA polymerase and helicase are involved in the replication process, but they do not directly join Okazaki fragments together. The leading and lagging strands refer to the two strands of DNA being replicated and do not play a direct role in joining Okazaki fragments together.

Question 6

Refer to the figure.  Which letter refers to an Okazaki fragment?

Accepted Answer

The arrow pointing to the fragment labeled "B" indicates an Okazaki fragment. Okazaki fragments are short, discontinuous segments of the lagging strand during DNA replication.

Question 7

Refer to the figure.  Which letter best indicates the lagging strand?

Accepted Answer

The answer of Refer to the figure.  Which letter...

Question 8

Refer to the figure.  Which structure illustrates a replication fork?

Accepted Answer

The answer of Refer to the figure.  Which structure...

Question 9

In organisms that contain circular DNA,

Accepted Answer

In circular DNA, such as in prokaryotes, replication is bidirectional, meaning the replication complex moves in both directions around the circle from a single origin of replication.

Question 10

The enzyme DNA ligase is required continuously during DNA replication in order for

Accepted Answer

DNA ligase is required to join the Okazaki fragments that are formed during the synthesis of the lagging strand in DNA replication. The fragments of the leading strand are synthesized continuously and do not require joining by DNA ligase. The parental strands are already joined together, so DNA ligase is not required for that either. Conversion of nucleoside triphosphates and the stability of the replication fork are not directly related to DNA ligase activity.

Question 11

During eukaryotic DNA synthesis, after repair the error rate is on the order of one wrong nucleotide per

Accepted Answer

The answer of During eukaryotic DNA synthesis, after repair the...

Question 12

Refer to the figure.  Which letter represents the leading strand?

Accepted Answer

The answer of Refer to the figure.  Which letter...

Question 13

In DNA replication, a sliding DNA clamp

Accepted Answer

A sliding DNA clamp increases the processivity of DNA polymerase, enabling it to catalyze the addition of many nucleotides to a growing DNA strand without dissociating from the template strand. Thus, it increases the number of nucleotides that can be polymerized at one time.

Question 14

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

Accepted Answer

Protective proteins such as shelterin bind to telomeres and form a protective cap, preventing the DNA repair system from recognizing the telomeres as breaks and from initiating the repair process. Telomerase, which adds telomere repeat sequences to the ends of chromosomes, is not directly involved in blocking the DNA repair system from accessing telomeres. DNA polymerase is responsible for replicating DNA rather than repairing it. The direction of DNA replication does not prevent the DNA repair system from repairing telomeres.

Question 15

Without DNA repair, the error rate of DNA polymerase is about one for every 100,000 bases replicated.If an organism has a haploid genome of 2 billion base pairs, how many mutations are likely to occur each time a diploid cell replicates its DNA?

Accepted Answer

Given the error rate of one in every 100,000 bases and a haploid genome size of 2 billion base pairs, each replication of the haploid genome would likely result in 20,000 errors (2,000,000,000 / 100,000 = 20,000). Since a diploid cell contains two sets of the genome, the number of mutations would double to 40,000 for each replication of a diploid cell's DNA.

Question 16

The telomeres at the ends of linear chromosomes allow

Accepted Answer

Telomeres at the ends of linear chromosomes protect the genetic information from being lost during each round of cell division. They also prevent the DNA repair machinery from mistaking the chromosome ends for broken pieces of DNA that need to be repaired. Telomeres shorten with each round of replication due to incomplete replication of the lagging strand. Telomerase is an enzyme that adds a short RNA primer to the end of the telomere, which can be extended by DNA polymerase to fill in the gap. Telomerase then adds additional repeats of the telomere sequence to the end of the chromosome, thereby protecting the genetic information and allowing normal cells to divide continuously.

Question 17

The enzyme that unwinds the DNA prior to replication is called

Accepted Answer

Helicase is the enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between the complementary base pairs. This process allows for the replication machinery to access the single strands of DNA for copying.

Question 18

Which of the following provides the correct order of events in the synthesis of the lagging strand?

Accepted Answer

The correct order for the synthesis of the lagging strand involves primase adding an RNA primer, DNA polymerase III extending the new DNA segment from the primer, DNA polymerase I removing the RNA primer and replacing it with DNA, and finally DNA ligase sealing the gaps between the newly synthesized Okazaki fragments.

Question 19

In a population of cells on the inner surface of the intestine, the cells frequently divide.Therefore, these cells are likely to

Accepted Answer

Cells that frequently divide require high levels of telomerase to maintain the length of their telomeres, which can shorten with each cell division.

Question 20

Which statement about telomerase is true?

Accepted Answer

Telomerase is an enzyme that can add telomeres to the ends of chromosomes, which become shorter with each round of DNA replication. This prevents the ends of the chromosomes from being eroded and protects the genetic information.

Quiz 13: Dna and Its Role in Heredity