Question 1

Phage X174 replication occurs by a

Accepted Answer

Phage X174 replication occurs through a rolling circle mechanism, which is a process where a single-stranded DNA virus generates a double-stranded form that serves as a template for producing multiple copies of the genome.

Question 2

A hallmark feature of rolling circle replication is

Accepted Answer

In rolling circle replication, one strand of the DNA is nicked and the 5' end is displaced, forming a 5' phosphate tail, while the 3' end serves as a primer for continuous DNA synthesis.

Question 3

Chromatin assembly factor 1 (CAF-1) is thought to aid replication by

Accepted Answer

CAF-1 is known for its role in bringing histones to the replication fork, which is essential for the assembly of newly synthesized DNA into chromatin.

Question 4

Two competing models to explain how nucleosomes are assembled behind replication forks differ by

Accepted Answer

The two models differ in whether histones H3 and H4 are transferred as dimers or tetramers to the daughter strands during nucleosome assembly.

Question 5

At the ends of chromosomes in eukaryotes, a problem occurs upon repeated DNA replication of the __________ strand. __________ is responsible for providing a solution to this problem.

Accepted Answer

The problem occurs on the lagging strand because standard DNA polymerases cannot replicate the very ends of chromosomes. Telomerase extends the telomeres, allowing complete replication without loss of important DNA sequences.

Question 6

Telomerase directly elongates

Accepted Answer

The answer of Telomerase directly elongates
...

Question 7

Telomerase is a ribonucleoprotein complex. The RNA component of the complex

Accepted Answer

The RNA component of telomerase serves as a template for the synthesis of telomere repeats, guiding the addition of specific nucleotide sequences to the ends of chromosomes.

Question 8

Telomerase is usually active in all of the following cell types except for:

Accepted Answer

Telomerase is an enzyme that adds DNA sequence repeats ("TTAGGG" in all vertebrates) to the 3' end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. This enzyme is typically active in single-celled eukaryotes, human germ-line cells (which give rise to gametes), and cancer cells, as these cells need to divide repeatedly or maintain their telomeres for longevity or uncontrolled growth. In contrast, most somatic cells, like human fibroblast cells, do not exhibit high levels of telomerase activity, leading to telomere shortening and eventual cell aging or apoptosis with successive cell divisions.

Question 9

The Hayflick limit is at least partly enforced by

Accepted Answer

The Hayflick limit, which is the number of times a normal human cell population will divide before cell division stops, is at least partly enforced by telomere shortening. Each time a cell divides, the telomeres at the ends of chromosomes get shorter, and when they become too short, the cell can no longer divide.

Question 10

Which of the following is not a function of telomeres?

Accepted Answer

Telomeres serve several key roles, including the protection of chromosome ends from degradation and the prevention of chromosome ends from being recognized as double-strand breaks. They act as a cellular clock by shortening with each cell division, which contributes to aging and cell death once they reach a critically short length. Shelterin is a protein complex that binds to telomeres, protecting them and regulating their maintenance. However, Cdc6 is involved in the initiation of DNA replication and is not directly related to the function of telomeres.

Question 11

TRF1/TRF2 and POT1 form a complex called ______________ that __________________.

Accepted Answer

Shelterin is a protein complex that specifically binds to and protects telomeres, the ends of chromosomes, from being recognized as DNA damage and thus prevents inappropriate repair mechanisms from being activated.

Question 12

Describe and give the results of the classic experiment that showed that DNA replication is semiconservative. What are the names of the scientists who carried out this experiment?

Accepted Answer

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Question 13

Describe electron microscopic evidence that DNA replication in E. coli is bidirectional.

Accepted Answer

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Question 14

Draw a diagram showing the addition of a new dNTP to the daughter strand during DNA replication. The diagram should be detailed enough to illustrate what is meant by the statement "DNA synthesis occurs from 5′ to 3′ ".

Accepted Answer

The answer of Draw a diagram showing the addition of...

Question 15

List the eukaryotic replicative DNA polymerases and their roles.

Accepted Answer

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Question 16

Why do you suppose eukaryotic cells "switch" from DNA polymerase alpha, which binds to primase and initiates DNA synthesis, to DNA polymerase delta/epsilon for elongation?

Accepted Answer

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Question 17

Of the three DNA polymerase in E. coli, which is essential for DNA replication?

Accepted Answer

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Question 18

Draw a bidirectional eukaryotic origin of replication. Label the 5′ and 3′ ends of each strand of the double helix. Label the lagging and leading strands at each replication fork. In which direction are new strands synthesized?

Accepted Answer

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Question 19

Outline the steps of nuclear chromosome replication in eukaryotes, starting from origin firing and ending with telomere replication.

Accepted Answer

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Question 20

Why are origins of replication often AT-rich?

Accepted Answer

The answer of Why are origins of replication often AT-rich?...

Quiz 6: DNA Replication and Telomere Maintenance