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

Tryptophan Operon and Attenuation

Genetics

12. Gene Regulation in Prokaryotes

Tryptophan Operon and Attenuation

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2:18 minutes

Problem 2i

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:
Attenuation

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Define attenuation: Attenuation is a regulatory mechanism in prokaryotes, particularly in operons like the trp operon, where transcription is prematurely terminated based on the interaction between transcription and translation processes.

Explain the mechanism: Attenuation relies on the formation of specific secondary structures in the mRNA transcript, such as stem-loop structures, which can either terminate transcription or allow it to continue.

Provide an example: In the trp operon of *E. coli*, when tryptophan levels are high, a leader peptide is translated, causing the formation of a terminator stem-loop in the mRNA. This terminator structure halts transcription before the structural genes of the operon are transcribed.

Contrast with low tryptophan levels: When tryptophan levels are low, the ribosome stalls during translation of the leader peptide due to a lack of charged tRNA^Trp. This allows the formation of an anti-terminator stem-loop, enabling transcription of the structural genes.

Summarize the importance: Attenuation provides a fine-tuned mechanism for regulating gene expression in response to metabolite levels, ensuring that resources are conserved when the end product (e.g., tryptophan) is abundant.

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Key Concepts

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

Attenuation

Attenuation is a regulatory mechanism in prokaryotic gene expression that controls transcription termination. It occurs in operons, where the formation of specific RNA structures in the leader region of mRNA can either promote or inhibit the continuation of transcription based on the presence of certain metabolites. For example, in the tryptophan operon, high levels of tryptophan lead to the formation of a hairpin structure that causes RNA polymerase to terminate transcription prematurely.

Operon

An operon is a cluster of genes under the control of a single promoter, allowing for coordinated expression of genes that often encode proteins with related functions. In prokaryotes, operons enable efficient regulation of gene expression in response to environmental changes. The classic example is the lac operon, which is involved in lactose metabolism and is activated in the presence of lactose while being repressed in its absence.

Transcriptional Regulation

Transcriptional regulation refers to the mechanisms that control the rate and timing of gene transcription, ensuring that genes are expressed at the right levels and times. This regulation can involve various factors, including transcription factors, enhancers, silencers, and regulatory RNAs. In the context of operons, transcriptional regulation allows cells to respond quickly to changes in their environment, such as nutrient availability.

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Multiple Choice

Attenuation uses what molecule to regulate the trp operon?

What is the name of the sequence responsible for regulating the trp operon through attenuation?

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Multiple Choice

If tryptophan levels are low, attenuation does what to the trp operon?

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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:

Corepressor

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Identify similarities and differences between an inducible operon and a repressible operon in terms of

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Textbook Question

Identify similarities and differences between an inducible operon and a repressible operon in terms of

The organization of structural genes of the operon.

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