Question 1

A new DNA strand elongates only in the 5' to 3' direction because

Accepted Answer

DNA polymerase can only add nucleotides to the free 3' end because it requires a free 3' hydroxyl group to form a phosphodiester bond between the new nucleotide and the previous one. This allows for the new strand to elongate in the 5' to 3' direction only, as nucleotides are added to the 3' end of the growing strand.

Question 2

In a linear eukaryotic chromatin sample, which of the following strands is looped into domains by scaffolding?

Accepted Answer

The 30-nm chromatin fiber is looped into domains by a proteinaceous scaffold. This folded structure is also known as the chromatin loop domain or loop domain. It is the next level of organization above the 10-nm chromatin fiber and is visible using electron microscopy. The other options do not involve looping into domains with scaffolding.

Question 3

Use the following list of choices for the following questions:
I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase
-Which of the enzymes separates the DNA strands during replication?

Accepted Answer

Helicase is responsible for unwinding the double-stranded DNA during replication, separating the two strands and creating a replication fork.

Question 4

Which of the following help(s)to hold the DNA strands apart while they are being replicated?

Accepted Answer

Single-strand binding proteins help to keep the DNA strands apart while they are being replicated. Primase is responsible for making RNA primers that DNA polymerase can add nucleotides to; ligase seals any gaps that may exist between Okazaki fragments during replication; DNA polymerase adds nucleotides to the growing DNA strand; and exonuclease helps to remove nucleotides from the DNA strand.

Question 5

The leading and the lagging strands differ in that

Accepted Answer

The leading strand is synthesized continuously in the 5' to 3' direction, which is the same as the movement of the replication fork, whereas the lagging strand is synthesized in the opposite direction and in short fragments called Okazaki fragments. This difference is due to the antiparallel nature of DNA strands.

Question 6

Which of the following would you expect of a eukaryote lacking telomerase?

Accepted Answer

Eukaryotes lacking telomerase would experience a reduction in chromosome length over time as the telomeres shorten. This would ultimately affect gametes as they would have progressively shorter chromosomes.

Question 7

Which of the following statements describes the eukaryotic chromosome?

Accepted Answer

The eukaryotic chromosome consists of a single linear molecule of double-stranded DNA plus proteins. This DNA is packed into chromatin, which is further organized into loops and domains.

Answer: B and C
 The nucleosome is the most basic functional subunit of the eukaryotic chromosome, consisting of DNA wrapped around a core of histone proteins. The number of genes on each chromosome is different in different cell types of an organism, with some genes being expressed in certain cells but not others.

Question 8

Studies of nucleosomes have shown that histones (except H1)exist in each nucleosome as two kinds of tetramers: one of 2 H2A molecules and 2 H2B molecules, and the other as 2 H3 and 2 H4 molecules. Which of the following is supported by this data?

Accepted Answer

The data suggests that the two types of histone tetramers associate to form an octamer, which is consistent with the known structure of a nucleosome where an octamer of histones is wrapped with DNA.

Question 9

Which of the following sets of materials are required by both eukaryotes and prokaryotes for replication?

Accepted Answer

Both eukaryotes and prokaryotes require double-stranded DNA, four kinds of dNTPs, primers, and origins for replication. The other answer choices include materials that are not necessarily required for replication by both types of cells.

Question 10

If a cell were unable to produce histone proteins, which of the following would be a likely effect?

Accepted Answer

Histone proteins play a key role in the packing of DNA into the nucleus. Without histones, the DNA would not be able to condense or pack tightly, preventing it from fitting inside the nucleus.

Question 11

To repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

Accepted Answer

The correct order for repairing a thymine dimer by nucleotide excision repair involves: 1) endonuclease to cut out the damaged DNA, 2) DNA polymerase I to synthesize new DNA to replace the removed section, and 3) DNA ligase to seal the new DNA into the existing strand.

Question 12

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that

Accepted Answer

The only difference between ATP and the nucleoside triphosphates used during DNA synthesis is the type of sugar molecule they contain. ATP contains the sugar ribose, while the nucleoside triphosphates used during DNA synthesis contain the sugar deoxyribose.

Question 13

What is the function of DNA polymerase III?

Accepted Answer

DNA polymerase III is the main polymerase responsible for adding nucleotides to the 3' end of a growing DNA strand during replication.

Answer: A, E are incorrect as DNA helicase is responsible for unwinding the DNA helix, and DNA ligase joins the newly synthesized DNA fragments together. B and D are also incorrect as DNA polymerase III does not seal or degrade damaged DNA molecules.

Question 14

Use the following list of choices for the following questions:
I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase
-Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?

Accepted Answer

DNA polymerase I removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments.

Question 15

Use the following list of choices for the following questions:
I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase
-Which of the enzymes covalently connects segments of DNA?

Accepted Answer

Ligase is the enzyme responsible for covalently connecting segments of DNA, particularly during the process of DNA replication and repair, by joining Okazaki fragments on the lagging strand.

Question 16

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells are impaired in what way?

Accepted Answer

Xeroderma pigmentosum is caused by impaired nucleotide excision repair, specifically the inability to repair thymine dimers caused by UV radiation. This results in a high risk of skin cancer and sun sensitivity.

Question 17

What is the function of topoisomerase?

Accepted Answer

Topoisomerase is responsible for relieving the strain on the DNA ahead of the replication fork. It breaks the DNA strands, rotates them, and then rejoins them to prevent supercoiling of the DNA during replication.

Answer: D 
 The unwinding of the double helix is performed by helicase. Topoisomerase is not directly involved in this process but works to relieve the stress on the double helix created by the unwinding process.

Therefore, the correct answer is A.

Question 18

Which of the following statements is true of histones?

Accepted Answer

Histone H1 is located outside the nucleosome core particle and is involved in the higher-order structure of chromatin by facilitating the packing of nucleosomes into a more compact structure.

Question 19

Use the following list of choices for the following questions:
I. helicase
II. DNA polymerase III
III. ligase
IV. DNA polymerase I
V. primase
-Which of the enzymes synthesizes short segments of RNA?

Accepted Answer

Primase is the enzyme that synthesizes short segments of RNA called primers.

Question 20

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

Accepted Answer

DNA ligase joins the Okazaki fragments together, which are the short DNA fragments formed on the lagging strand during DNA replication.

Answer: A, B, D, E are incorrect 
 None of these options describe the role of DNA ligase in the elongation of the lagging strand. DNA ligase does not synthesize RNA nucleotides to make a primer, it does not catalyze the lengthening of telomeres, it does not unwind the parental double helix, and it does not stabilize the unwound parental DNA.

Quiz 16: The Molecular Basis of Inheritance