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

10. Transcription

Transcription in Prokaryotes

Genetics

10. Transcription

Transcription in Prokaryotes

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3:17 minutes

Problem 20d

Textbook Question

Wild-type E. coli grows best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at What term best characterizes the type of mutation exhibited by the mutant bacterial strain? (Hint: The term was used in Chapter 4 to describe the Himalayan allele of the mammalian C gene.)

Verified step by step guidance

Step 1: Begin by understanding the problem. The question describes a mutation in the sigma subunit of RNA polymerase in E. coli. This mutation affects the stability of the holoenzyme at higher temperatures, leading to its denaturation and cessation of transcription at 42°C. The goal is to characterize the type of mutation based on its temperature-dependent behavior.

Step 2: Recall the concept of temperature-sensitive mutations. These mutations result in proteins that function normally at a permissive temperature (e.g., 37°C) but lose functionality at a restrictive temperature (e.g., 42°C). This is a key clue to identifying the mutation type.

Step 3: Relate this to the hint provided in the problem. The hint references the Himalayan allele of the mammalian C gene, which is a classic example of a temperature-sensitive mutation. In Himalayan rabbits, the C gene is functional at cooler temperatures (e.g., extremities of the body) but nonfunctional at warmer temperatures (e.g., the body core).

Step 4: Apply this concept to the mutant E. coli strain. The mutant RNA polymerase holoenzyme is stable and functional at 37°C (permissive temperature) but becomes destabilized and nonfunctional at 42°C (restrictive temperature). This temperature-dependent behavior aligns with the definition of a temperature-sensitive mutation.

Step 5: Conclude that the term best characterizing the mutation in the mutant bacterial strain is 'temperature-sensitive mutation,' as it describes the loss of function at higher, restrictive temperatures while maintaining normal function at lower, permissive temperatures.

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Key Concepts

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

Temperature Sensitivity

Temperature sensitivity refers to the dependence of an organism's biological processes on temperature. In the context of E. coli, this concept highlights how the stability and functionality of proteins, such as RNA polymerase, can be affected by temperature changes. A temperature-sensitive mutation may result in a protein that functions normally at lower temperatures but becomes unstable or inactive at higher temperatures.

Sigma Factor and RNA Polymerase

The sigma factor is a protein that associates with RNA polymerase to facilitate the initiation of transcription in bacteria. It helps the RNA polymerase holoenzyme recognize specific promoter regions on DNA. Mutations in the sigma factor can lead to changes in the stability and activity of the RNA polymerase, impacting the transcription process, especially under varying environmental conditions like temperature.

Conditional Mutation

A conditional mutation is a genetic alteration that results in a phenotype that is only expressed under certain environmental conditions, such as temperature. In this case, the E. coli strain exhibits normal transcription at 37°C but fails to do so at 42°C due to the destabilization of the RNA polymerase holoenzyme. This type of mutation is crucial for understanding how organisms adapt to different environments and can be linked to specific alleles, such as the Himalayan allele mentioned in the question.

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Related Practice

Textbook Question

The segment of the bacterial TrpA gene involved in intrinsic termination of transcription is the following:

3'-TGGGTCGGGGCGGATTACTGCCCCGAAAAAAAACTTG-5'

5'-ACCCAGCCCCGCCTAATGACGGGGCTTTTTTTTGAAC-3'

Label the template and coding DNA strands.

431

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Textbook Question

The segment of the bacterial TrpA gene involved in intrinsic termination of transcription is the following:

3'-TGGGTCGGGGCGGATTACTGCCCCGAAAAAAAACTTG-5'

5'-ACCCAGCCCCGCCTAATGACGGGGCTTTTTTTTGAAC-3' Draw the mRNA structure that forms during transcription of this segment of the TrpA gene.

467

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Textbook Question

The segment of the bacterial TrpA gene involved in intrinsic termination of transcription is the following:

3'-TGGGTCGGGGCGGATTACTGCCCCGAAAAAAAACTTG-5'

5'-ACCCAGCCCCGCCTAATGACGGGGCTTTTTTTTGAAC-3'

Explain how a sequence of this type leads to intrinsic termination of transcription.

466

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Textbook Question

Describe the structure of RNA polymerase in bacteria. What is the core enzyme? What is the role of the σ subunit?

781

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Textbook Question

Wild-type E. coli grows best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at 42°C

Wild-type E. coli grow best at 37°C but can grow efficiently up to 42°C. An E. coli strain has a mutation of the sigma subunit that results in an RNA polymerase holoenzyme that is stable and transcribes at wild-type levels at 37°C. The mutant holoenzyme is progressively destabilized as the temperature is raised, and it completely denatures and ceases to carry out transcription at 42°C. Relative to wild-type growth, characterize the ability of the mutant strain to carry out transcription at 37°C

428

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Textbook Question

Write a paragraph describing the abbreviated chemical reactions that summarize RNA polymerase-directed transcription.

481

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