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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1:40 minutes

Problem 20a

Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Newly synthesized DNA contains many mismatched base pairs.

Verified step by step guidance

Step 1: Understand the problem. The presence of many mismatched base pairs in newly synthesized DNA suggests an issue with the fidelity of DNA replication. This typically points to a defect in the proofreading or mismatch repair mechanisms.

Step 2: Recall the role of DNA polymerase. DNA polymerase is responsible for synthesizing new DNA strands during replication. It also has a proofreading function, which uses its 3' to 5' exonuclease activity to remove mismatched bases and replace them with the correct ones.

Step 3: Consider the possibility of a mutation affecting DNA polymerase. A temperature-sensitive mutation in the gene encoding DNA polymerase could impair its proofreading ability at non-optimal temperatures, leading to the accumulation of mismatched base pairs.

Step 4: Explore mismatch repair systems. If the proofreading function of DNA polymerase is intact, the issue could lie in the mismatch repair system, which corrects errors missed during replication. Mutations in genes encoding mismatch repair enzymes (e.g., MutS, MutL, or MutH) could lead to the observed phenotype.

Step 5: Predict the affected enzyme or function. Based on the information provided, the mutation likely affects either the proofreading activity of DNA polymerase or the mismatch repair system. Further experimental analysis would be needed to pinpoint the exact enzyme or function involved.

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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 exact copy of the genetic material. This process involves various enzymes, including DNA polymerases, which synthesize new DNA strands by adding nucleotides complementary to the template strand. Errors during replication can lead to mismatched base pairs, which can affect the integrity of the genetic information.

DNA Repair Mechanisms

Cells have evolved several DNA repair mechanisms to correct mismatched base pairs that occur during DNA replication. One key mechanism is the mismatch repair system, which identifies and repairs incorrectly paired nucleotides. If these repair systems are compromised, as may be the case in temperature-sensitive mutants, the frequency of mismatches can increase, leading to mutations and potential cellular dysfunction.

Temperature-Sensitive Mutations

Temperature-sensitive mutations are genetic alterations that result in a protein functioning normally at one temperature but becoming inactive or dysfunctional at another. In the context of E. coli, these mutations can affect enzymes involved in DNA replication or repair, leading to increased errors such as mismatched base pairs when the organism is exposed to non-permissive temperatures. Understanding these mutations helps in predicting the specific enzyme or function that is impaired.

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Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Supercoiled strands remain after replication, which is never completed.

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Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Synthesis is very slow.

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Textbook Question

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

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Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Okazaki fragments accumulate, and DNA synthesis is never completed.

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Textbook Question

DNA supercoiling, which occurs when coiling tension is generated ahead of the replication fork, is relieved by DNA gyrase. Supercoiling may also be involved in transcription regulation. Researchers discovered that enhancers operating over a long distance (2500 bp) are dependent on DNA supercoiling, while enhancers operating over shorter distances (110 bp) are not so dependent [Liu et al. (2001). Proc. Natl. Acad. Sci. USA 98:14,883–14,888]. Using a diagram, suggest a way in which supercoiling may positively influence enhancer activity over long distances.

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Textbook Question

Raymond Rodriguez and colleagues demonstrated conclusively that DNA replication in E. coli is bidirectional. Explain why locating the origin of replication on one side of the circular chromosomes and the terminus of replication on the opposite side of the chromosome supported this conclusion.

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Textbook Question

While many commonly used antibiotics interfere with protein synthesis or cell wall formation, clorobiocin, one of several antibiotics in the aminocoumarin class, inhibits the activity of bacterial DNA gyrase. Similar drugs have been tested as treatments for human cancer. How might such drugs be effective against bacteria as well as cancer?

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Textbook Question

Joel Huberman and Arthur Riggs used pulse–chase labeling to examine the replication of DNA in mammalian cells. Briefly describe the Huberman–Riggs experiment, and identify how the results exclude a unidirectional model of DNA replication.

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Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation. Newly synthesized DNA contains many mismatched base pairs.

Key Concepts

DNA Replication

DNA Repair Mechanisms

Temperature-Sensitive Mutations

Watch next

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Newly synthesized DNA contains many mismatched base pairs.