Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

8. DNA Replication

Telomeres and Telomerase

Genetics

8. DNA Replication

Telomeres and Telomerase

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2:14 minutes

Problem 11b

Textbook Question

There is a problem completing the replication of linear chromosomes at their ends. What is the function of telomerase, and how does it operate to synthesize telomeres?

Verified step by step guidance

Understand the problem: Linear chromosomes face an issue during replication because DNA polymerase cannot fully replicate the ends of the lagging strand, leading to progressive shortening of chromosomes with each cell division. This is known as the 'end-replication problem.'

Learn the role of telomerase: Telomerase is an enzyme that solves the end-replication problem by adding repetitive nucleotide sequences (telomeres) to the ends of linear chromosomes, preventing their shortening and maintaining genomic stability.

Explore the structure of telomerase: Telomerase is a ribonucleoprotein complex composed of a protein component (telomerase reverse transcriptase, TERT) and an RNA component (TERC). The RNA component serves as a template for synthesizing telomeric DNA.

Understand the mechanism of telomerase action: Telomerase binds to the overhanging single-stranded DNA at the end of the chromosome. Using its RNA template, it synthesizes complementary DNA sequences through reverse transcription, extending the telomere region.

Learn the significance of telomerase activity: Telomerase is highly active in germ cells, stem cells, and certain cancer cells, ensuring their ability to divide indefinitely. In most somatic cells, telomerase activity is low or absent, leading to gradual telomere shortening and cellular aging.

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Key Concepts

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

Telomeres

Telomeres are repetitive nucleotide sequences located at the ends of linear chromosomes. They protect the chromosome from deterioration or fusion with neighboring chromosomes, which is crucial for maintaining genomic stability. Each time a cell divides, telomeres shorten, and when they become too short, the cell can no longer divide, leading to cellular aging.

Telomerase

Telomerase is an enzyme that adds nucleotide sequences to the ends of telomeres, counteracting the shortening that occurs during DNA replication. It is composed of a protein component and an RNA template that guides the addition of telomeric repeats. Telomerase is particularly active in stem cells and cancer cells, allowing them to maintain telomere length and continue dividing.

Mechanism of Telomerase Action

Telomerase operates by binding to the 3' end of a telomere and extending it using its RNA template. This process involves reverse transcription, where the RNA sequence is used to synthesize DNA. By elongating the telomeres, telomerase helps prevent the loss of essential genetic information during cell division, thus playing a critical role in cellular longevity and proliferation.

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Related Practice

Multiple Choice

Lagging strand telomeres are replicated in the same way as the rest of the chromosome

Which cell type contains the most telomerase

Telomeres are composed of what type of DNA molecule?

In the discussion, we focused on how DNA is organized at the chromosomal level. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions:

How do we know that satellite DNA consists of repetitive sequences and has been derived from regions of the centromere?

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Textbook Question

There is a problem completing the replication of linear chromosomes at their ends. Describe the problem and identify why telomeres shorten in each replication cycle.

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Textbook Question

In 1994, telomerase activity was discovered in human cancer cell lines. Although telomerase is not active in most human adult cells, all cells do contain the genes for telomerase proteins and telomerase RNA. Since inappropriate activation of telomerase may contribute to cancer, why do you think the genes coding for this enzyme have been maintained in the human genome throughout evolution? Are there any types of human body cells where telomerase activation would be advantageous or even necessary? Explain.

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Textbook Question

Telomeres are found at the ends of eukaryotic chromosomes. Why is telomerase usually active in germ-line cells but not in somatic cells?

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Textbook Question

Telomeres are found at the ends of eukaryotic chromosomes. What is the functional role of telomeres?

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