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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2:38 minutes

Problem 10

Textbook Question

DNA polymerase III is the main DNA-synthesizing enzyme in bacteria. Describe how it carries out its role of elongating a strand of DNA.

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DNA polymerase III begins its role by binding to the primer, which is a short RNA sequence synthesized by primase. This primer provides a free 3'-OH group necessary for DNA polymerase III to initiate DNA synthesis.

The enzyme elongates the DNA strand by adding nucleotides complementary to the template strand. It follows the base-pairing rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

DNA polymerase III synthesizes the new strand in the 5' to 3' direction, meaning it adds nucleotides to the 3'-OH end of the growing strand. This directionality is crucial for proper DNA replication.

The enzyme has high processivity, meaning it can add thousands of nucleotides without dissociating from the DNA template. This is facilitated by the sliding clamp protein, which holds DNA polymerase III tightly to the DNA strand.

DNA polymerase III also has proofreading activity through its 3' to 5' exonuclease function. If an incorrect nucleotide is incorporated, the enzyme can remove it and replace it with the correct one, ensuring high fidelity during DNA replication.

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Key Concepts

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

DNA Replication

DNA replication is the biological process by which a cell duplicates its DNA, ensuring that each daughter cell receives an identical copy. This process involves unwinding the double helix and synthesizing new strands complementary to the original templates. DNA polymerase III plays a crucial role in this process by adding nucleotides to the growing DNA strand.

DNA Polymerase III Function

DNA polymerase III is a multi-subunit enzyme responsible for synthesizing new DNA strands during replication. It adds nucleotides in a 5' to 3' direction, using the existing template strand as a guide. This enzyme also has proofreading capabilities, allowing it to correct errors during DNA synthesis, which is vital for maintaining genetic fidelity.

Leading and Lagging Strands

During DNA replication, the two strands of the double helix are replicated differently. The leading strand is synthesized continuously in the direction of the replication fork, while the lagging strand is synthesized in short segments called Okazaki fragments, which are later joined together. DNA polymerase III is involved in synthesizing both strands, but its activity differs based on the strand being replicated.

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Textbook Question

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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Textbook Question

Kornberg showed that nucleotides are added to the 3' end of each growing DNA strand. In what way does an exposed 3'-OH group participate in strand elongation?

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Textbook Question

What was the significance of the polA1 mutation?

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Textbook Question

Explain how RNA participates in DNA replication.

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Textbook Question

Summarize and compare the properties of DNA polymerase I, II, and III.