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

12. Gene Regulation in Prokaryotes

Lac Operon

Genetics

12. Gene Regulation in Prokaryotes

Lac Operon

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2:38 minutes

Problem 3b

Textbook Question

Answer these questions concerning promoters.
What is the common structure of a bacterial promoter with respect to consensus sequences?

Verified step by step guidance

Understand that a bacterial promoter is a DNA sequence that facilitates the binding of RNA polymerase to initiate transcription. Promoters are located upstream of the transcription start site.

Recognize that bacterial promoters typically contain two key consensus sequences: the -10 region (Pribnow box) and the -35 region. These sequences are named based on their approximate distance in base pairs upstream from the transcription start site (+1).

The -10 region consensus sequence is typically TATAAT. This sequence is important for the unwinding of DNA, as it is rich in adenine (A) and thymine (T), which are easier to separate due to having only two hydrogen bonds.

The -35 region consensus sequence is typically TTGACA. This sequence is recognized by the sigma factor of RNA polymerase, which helps the enzyme bind to the promoter.

Note that the spacing between the -10 and -35 regions is also important, usually around 16-18 base pairs. This spacing allows proper alignment of RNA polymerase for efficient transcription initiation.

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Key Concepts

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

Bacterial Promoter Structure

Bacterial promoters are specific DNA sequences located upstream of a gene that facilitate the binding of RNA polymerase for transcription initiation. They typically contain two key regions: the -10 region (Pribnow box) and the -35 region, which are recognized by sigma factors. The spacing between these regions is crucial for effective transcription initiation.

Consensus Sequences

Consensus sequences are short, recurring patterns in DNA that are recognized by proteins, such as transcription factors. In bacterial promoters, the consensus sequences at the -10 and -35 regions represent the most common nucleotides found in these positions across different genes, providing a template for RNA polymerase binding and transcription regulation.

Transcription Initiation

Transcription initiation is the process by which RNA polymerase binds to a promoter and begins synthesizing RNA from a DNA template. In bacteria, this process is highly regulated and relies on the interaction between the RNA polymerase, sigma factors, and the consensus sequences of the promoter, ensuring that genes are expressed at the right time and in the right amounts.

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Textbook Question

Transcriptional regulation of operon gene expression involves the interaction of molecules with one another and of regulatory molecules with segments of DNA. In this context, define and give an example of each of the following:

Inducer

Repressor

Operator

Why is it essential that bacterial cells be able to regulate the expression of their genes? What are the energetic and evolutionary advantages of regulated gene expression? Is the expression of all bacterial genes subject to regulated expression? Compare and contrast the difference between regulated gene expression and constitutive gene expression.

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Contrast positive versus negative control of gene expression.

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Contrast the role of the repressor in an inducible system and in a repressible system.

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The transcription of -galactosidase and permease is inducible in lac⁺ bacteria with a wild-type lac operon. Explain the mechanism by which lactose gains access to the cell to induce transcription of the genes.

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Textbook Question

For the lac genotypes shown in the following table, predict whether the structural genes (Z) are constitutive, permanently repressed, or inducible in the presence of lactose.Genotype Constitutive Repressed InducibleI⁺O⁺Z⁺ xI⁻O⁺Z⁺I⁻OᶜZ⁺I⁻OᶜZ⁺/F'O⁺I⁺OᶜZ⁺/F'O⁺IˢO⁺Z⁺IˢO⁺Z⁺/F'I⁺

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