Ch. 15 - DNA and the Gene: Synthesis and Repair

Freeman - Biological Science 7th Edition

Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook

Freeman 7th Edition

Ch. 15 - DNA and the Gene: Synthesis and Repair

Problem 4

Chapter 15, Problem 4

Telomerase synthesizes DNA in the _____ direction.

Verified step by step guidance

Understand the role of telomerase: Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of chromosomes, known as telomeres, to prevent them from shortening during cell division.

Recognize the direction of DNA synthesis: DNA synthesis typically occurs in the 5' to 3' direction. This means that new nucleotides are added to the 3' end of the growing DNA strand.

Identify the template used by telomerase: Telomerase uses an RNA template that is part of the enzyme itself to extend the 3' end of the DNA strand.

Consider the mechanism of telomerase action: Telomerase binds to the 3' end of the telomere and uses its RNA component to synthesize DNA in the 5' to 3' direction, extending the telomere.

Review the importance of telomerase: By extending telomeres, telomerase plays a crucial role in cellular aging and cancer, as it allows cells to divide without losing important DNA sequences.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Telomerase Function

Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of chromosomes, known as telomeres. This process helps prevent the loss of important DNA sequences during cell division, thereby maintaining chromosome integrity and stability. Telomerase is particularly active in stem cells and cancer cells, where it supports continuous cell division.

DNA Synthesis Direction

DNA synthesis occurs in the 5' to 3' direction, meaning that new nucleotides are added to the 3' end of the growing DNA strand. This directionality is due to the enzymatic mechanism of DNA polymerases, which require a free 3' hydroxyl group to add new nucleotides. Telomerase, like other DNA polymerases, follows this 5' to 3' synthesis rule.

Telomere Structure

Telomeres are repetitive nucleotide sequences at the ends of linear chromosomes, protecting them from degradation and fusion with neighboring chromosomes. In humans, the sequence is typically TTAGGG, repeated thousands of times. Telomeres shorten with each cell division, and telomerase helps counteract this shortening in certain cell types, contributing to cellular longevity.

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Telomeres

Related Practice

Textbook Question

Which of the following is not a property of DNA polymerase?

a. It adds dNTPs only in the 5'→3' direction.

b. It requires a primer to begin synthesis.

c. It opens the two strands of DNA at the replication fork.

d. Its exonuclease activity is involved in proofreading.

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Textbook Question

What is the function of primase?

a. Synthesis of the repetitive, short double-stranded DNA sequences required by DNA polymerase.

b. Synthesis of a short RNA strand that is complementary to single-stranded DNA.

c. Closing the gap at the 3′ end of DNA after excision repair.

d. Removing primers and synthesizing a short section of DNA to replace them.

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Textbook Question

How are Okazaki fragments synthesized?

a. By using the leading-strand template, and synthesizing 5'→3'

b. By using the leading-strand template, and synthesizing 3'→5'

c. By using the lagging-strand template, and synthesizing 5'→3'

d. By using the lagging-strand template, and synthesizing 3'→5'.

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Textbook Question

Researchers design experiments so that only one thing is different between the treatments that are being compared. In the Hershey–Chase experiment, what was this single difference?

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Textbook Question

Analyze the following statements about DNA synthesis. Select True or False for each statement.

T/FAn RNA polymerase is essential for DNA synthesis.

T/FOkazaki fragments would be unnecessary if DNA polymerase could synthesize DNA in both the 3'→5' and 5'→3' directions.

T/FDNA ligase is used more frequently on the lagging strand than on the leading strand.

T/FToposiomerase is required to separate the two strands of DNA at the replication fork.

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Textbook Question

How does telomerase prevent linear chromosomes from shortening during replication?

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