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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3:15 minutes

Problem 20a

Textbook Question

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

Verified step by step guidance

Understand the role of the sigma subunit in RNA polymerase: The sigma subunit is a critical component of the RNA polymerase holoenzyme in prokaryotes. It is responsible for recognizing promoter sequences and initiating transcription. A mutation in the sigma subunit can affect the stability and function of the holoenzyme.

Analyze the given information about the mutant strain: The mutant RNA polymerase holoenzyme is stable and transcribes at wild-type levels at 37°C. This means that at this temperature, the mutation does not impair the ability of the enzyme to initiate and carry out transcription.

Compare the mutant strain to the wild-type strain at 37°C: Since the mutant holoenzyme is stable and transcribes at wild-type levels at 37°C, the mutant strain should be able to carry out transcription as efficiently as the wild-type strain at this temperature.

Consider the temperature sensitivity of the mutant holoenzyme: The problem specifies that the mutant holoenzyme becomes progressively destabilized as the temperature increases beyond 37°C, eventually ceasing transcription at 42°C. However, this temperature sensitivity does not affect its function at 37°C.

Conclude the transcription ability of the mutant strain at 37°C: Relative to the wild-type strain, the mutant strain is expected to carry out transcription normally at 37°C, as the mutation does not impair the holoenzyme's stability or transcriptional activity at this temperature.

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Key Concepts

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

RNA Polymerase Function

RNA polymerase is an essential enzyme responsible for synthesizing RNA from a DNA template during transcription. In E. coli, the holoenzyme consists of the core enzyme and a sigma factor that helps initiate transcription at specific promoters. Understanding how mutations in the sigma subunit affect the stability and function of RNA polymerase is crucial for analyzing the transcriptional capabilities of the mutant strain.

Temperature Effects on Enzyme Activity

Enzymes, including RNA polymerase, have optimal temperature ranges for activity. At temperatures above or below this range, enzyme stability and function can be compromised. In this case, the mutant E. coli strain's ability to transcribe at 37°C compared to its performance at higher temperatures is essential for understanding how temperature influences enzyme activity and overall cellular function.

Mutations and Phenotypic Expression

Mutations are changes in the DNA sequence that can lead to alterations in protein structure and function. The specific mutation in the sigma subunit of the E. coli strain affects the stability of the RNA polymerase holoenzyme, which in turn influences transcription efficiency. Analyzing how this mutation impacts the strain's growth and transcription at 37°C relative to wild-type provides insights into the relationship between genotype and phenotype.

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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?

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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 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.)

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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

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

A mutant strain of Salmonella bacteria carries a mutation of the rho protein that has full activity at 37°C but is completely inactivated when the mutant strain is grown at 40°C. Speculate about the kind of differences you would expect to see if you compared a broad spectrum of mRNAs from the mutant strain grown at 37°C and the same spectrum of mRNAs from the strain when grown at 40°C.

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Textbook Question

The DNA sequence below gives the first 12 base pairs of the transcribed region of a gene, and the template and nontemplate strands of DNA are identified. The transcription start is the thymine nucleotide at the end of the sequence given. Use the diagram to answer the list of questions. Make a copy of the diagram before you begin answering the questions, or have one group member diagram the answers for bacteria and another group member diagram the answers for eukaryotes. Nontemplate strand ___________TTGCTACGGTCA___________

Template strand ___________AACGATGCCAGT___________

Write the anticipated bacterial consensus sequence(s) in the approximate position(s) on the diagram.

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