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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0:41 minutes

Problem 5

Textbook Question

Predict the results of the experiment by Taylor, Woods, and Hughes if replication were
(a) conservative and
(b) dispersive.

Verified step by step guidance

Understand the experimental setup: Taylor, Woods, and Hughes used root-tip cells of Vicia faba (broad bean) to study DNA replication. They incorporated radioactive thymidine (³H-thymidine) into DNA during replication and used autoradiography to visualize the distribution of the labeled DNA.

Review the conservative replication model: In conservative replication, the original DNA molecule remains intact, and a completely new DNA molecule is synthesized. This means that after replication, one DNA molecule will consist entirely of the original strands, and the other will consist entirely of newly synthesized strands.

Predict the results for conservative replication: In the first round of replication, only one of the two DNA molecules would be radioactive (newly synthesized strands). In the second round, half of the DNA molecules would be radioactive, and the other half would remain unlabeled, as the original DNA molecule is conserved and does not incorporate radioactive thymidine.

Review the dispersive replication model: In dispersive replication, the original DNA strands are fragmented, and new DNA is synthesized in a patchwork manner. Each resulting DNA molecule contains interspersed segments of old and new DNA.

Predict the results for dispersive replication: After the first round of replication, both DNA molecules would show a uniform distribution of radioactivity, as old and new DNA are mixed within each strand. In subsequent rounds, the radioactivity would become increasingly diluted as more unlabeled thymidine is incorporated into the DNA.

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Key Concepts

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

DNA Replication Models

DNA replication can occur through different models: conservative, semi-conservative, and dispersive. In the conservative model, the original DNA molecule remains intact, and an entirely new copy is made. In the dispersive model, the original DNA is broken into pieces, and new DNA is interspersed with the old, resulting in hybrid molecules. Understanding these models is crucial for predicting experimental outcomes.

Semi-Conservative Replication

The semi-conservative model of DNA replication, proposed by Watson and Crick, suggests that each new DNA molecule consists of one original strand and one newly synthesized strand. This model was confirmed by the Meselson-Stahl experiment, which demonstrated that DNA replication conserves half of the parental DNA in each daughter molecule. This concept is essential for understanding how genetic information is accurately passed on during cell division.

Experimental Predictions

In the context of the Taylor, Woods, and Hughes experiment, predictions about the outcomes of conservative and dispersive replication can be made based on the structure of the resulting DNA. For conservative replication, one would expect to see distinct bands of original and new DNA, while dispersive replication would yield a more uniform distribution of DNA density. These predictions help in interpreting experimental results and understanding the nature of DNA replication.

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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?

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

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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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Compare conservative, semiconservative, and dispersive modes of DNA replication.

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Describe the role of ¹⁵N in the Meselson–Stahl experiment.

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What are the requirements for in vitro synthesis of DNA under the direction of DNA polymerase I?

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Textbook Question

In Kornberg's initial experiments, it was rumored that he grew E. coli in Anheuser-Busch beer vats. (Kornberg was working at Washington University in St. Louis.) Why do you think this might have been helpful to the experiment?

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Textbook Question

How did Kornberg assess the fidelity of DNA polymerase I in copying a DNA template?

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Textbook Question

Which characteristics of DNA polymerase I raised doubts that its in vivo function is the synthesis of DNA leading to complete replication?

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