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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1:47 minutes

Problem 1e

Textbook Question

How do we know that the trp operon is a repressible control system, in contrast to the lac operon, which is an inducible control system?

Verified step by step guidance

Understand the difference between repressible and inducible systems: A repressible system, like the trp operon, is typically active and gets turned off (repressed) when a specific molecule (corepressor) is present. An inducible system, like the lac operon, is typically inactive and gets turned on (induced) when a specific molecule (inducer) is present.

Examine the trp operon: The trp operon is involved in the synthesis of tryptophan. When tryptophan levels are high, tryptophan acts as a corepressor by binding to the trp repressor protein. This complex then binds to the operator region of the operon, preventing transcription of the genes involved in tryptophan synthesis.

Examine the lac operon: The lac operon is involved in the metabolism of lactose. When lactose is present, it is converted into allolactose, which acts as an inducer. Allolactose binds to the lac repressor protein, causing it to release from the operator region, allowing transcription of the genes involved in lactose metabolism.

Compare experimental evidence: In experiments, the trp operon is shown to be active in the absence of tryptophan and repressed in its presence, demonstrating its repressible nature. Conversely, the lac operon is inactive in the absence of lactose and becomes active when lactose is present, demonstrating its inducible nature.

Conclude based on the regulatory mechanisms: The trp operon is a repressible system because it is turned off in the presence of its end product (tryptophan), while the lac operon is an inducible system because it is turned on in the presence of its substrate (lactose). This distinction is based on the molecular interactions of the repressor proteins and their respective effectors (corepressor or inducer).

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Key Concepts

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

Operon Model

The operon model is a genetic regulatory system found in bacteria, where a group of genes is controlled by a single promoter and regulated together. This model helps explain how genes can be turned on or off in response to environmental changes, allowing bacteria to efficiently manage their metabolic processes.

Repressible vs. Inducible Operons

Repressible operons, like the trp operon, are typically turned off and can be inhibited by the presence of a specific molecule, such as tryptophan. In contrast, inducible operons, such as the lac operon, are usually off and can be activated in response to an inducer, like lactose, allowing the bacteria to adapt to different nutrient sources.

Feedback Inhibition

Feedback inhibition is a regulatory mechanism where the end product of a metabolic pathway inhibits an earlier step in the pathway. In the case of the trp operon, high levels of tryptophan signal the operon to shut down gene expression, preventing the unnecessary production of tryptophan when it is already abundant.

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Related Practice

Multiple Choice

Tryptophan regulates the trp operon by doing what?

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?

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

Corepressor

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

The presence and action of allosteric regulatory molecules.

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