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

Overview of DNA Replication

Genetics

8. DNA Replication

Overview of DNA Replication

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2:19 minutes

Problem 1e

Textbook Question

In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?
What observations reveal that a 'telomere problem' exists during eukaryotic DNA replication, and how did we learn of the solution to this problem?

Verified step by step guidance

Understand the 'telomere problem': During eukaryotic DNA replication, the lagging strand synthesis cannot fully replicate the ends of linear chromosomes due to the requirement for a primer and the inability of DNA polymerase to synthesize DNA in the 3' to 5' direction. This results in progressive shortening of telomeres with each cell division.

Recognize the observations that revealed the problem: Scientists observed that telomeres, the repetitive DNA sequences at the ends of chromosomes, become shorter in cells that divide repeatedly. This shortening was linked to cellular aging and eventual senescence.

Learn about the discovery of telomerase: Researchers identified an enzyme called telomerase, which adds repetitive nucleotide sequences to the ends of telomeres, counteracting the shortening. Telomerase contains an RNA template that guides the addition of telomeric repeats.

Understand the mechanism of telomerase: Telomerase extends the 3' overhang of the telomere, allowing the lagging strand synthesis machinery to complete replication of the chromosome ends. This prevents the loss of genetic information during replication.

Explore experimental evidence: Experiments with telomerase-deficient cells showed accelerated telomere shortening and premature cellular aging, while cells with active telomerase maintained telomere length and extended their replicative lifespan. This confirmed the role of telomerase in solving the 'telomere problem'.

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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 eukaryotic chromosomes, protecting them from degradation and preventing the loss of essential genetic information during DNA replication. As cells divide, telomeres shorten, which can lead to cellular aging and limit the number of times a cell can divide, a phenomenon known as the Hayflick limit.

DNA Replication

DNA replication is the biological process by which a cell duplicates its DNA before cell division. This process involves unwinding the double helix and synthesizing new strands using existing strands as templates. However, the mechanism of replication cannot fully replicate the ends of linear chromosomes, leading to the 'telomere problem' where important genetic information could be lost.

Telomerase

Telomerase is an enzyme that adds repetitive nucleotide sequences to the ends of telomeres, counteracting their shortening during DNA replication. It is particularly active in stem cells and cancer cells, allowing them to maintain telomere length and continue dividing. The discovery of telomerase provided insights into how cells can overcome the limitations imposed by telomere shortening.

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Related Practice

Multiple Choice

DNA replication synthesizes DNA in which direction?

What would happen to DNA replication in DNA polymerase lost its 3' to 5' exonuclease activity?

Which of the following proteins is responsible for synthesizing RNA primers?

The short DNA fragments created during lagging strand replication are called what?

In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

How do we know that DNA synthesis is discontinuous on one of the two template strands?

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Textbook Question

How do we know that in vivo DNA synthesis occurs in the 5' to 3' direction?

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Textbook Question

How was it demonstrated that DNA synthesis occurs under the direction of DNA polymerase III and not polymerase I?

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Textbook Question

Write a short essay that distinguishes between the terms replication and synthesis, as applied to DNA. Which of the two is most closely allied with the field of biochemistry?

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