Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

16. Regulation of Expression

Prokaryotic Gene Regulation via Operons

General Biology

16. Regulation of Expression

Prokaryotic Gene Regulation via Operons

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3:43 minutes

Problem 7

Textbook Question

Explain why it makes sense for the lexA regulatory gene of the SOS regulon to be expressed constitutively.

Verified step by step guidance

Understand the context: The SOS regulon is a group of genes in bacteria that are activated in response to DNA damage. The lexA gene encodes the LexA protein, which acts as a repressor for the SOS genes under normal conditions.

Recognize the role of LexA: LexA binds to the operator regions of SOS genes, preventing their transcription. This repression ensures that the SOS response is not activated unnecessarily, which could be wasteful or harmful to the cell.

Consider the need for constant regulation: Since DNA damage can occur at any time, the cell must always have a mechanism in place to repress the SOS genes when there is no damage. This requires a steady supply of LexA protein, which is achieved through constitutive expression of the lexA gene.

Understand the balance: Constitutive expression of lexA ensures that the cell maintains a baseline level of LexA protein. When DNA damage occurs, the RecA protein becomes activated and facilitates the self-cleavage of LexA, lifting the repression and allowing the SOS genes to be expressed.

Conclude the reasoning: Constitutive expression of lexA is essential because it ensures the cell is always prepared to regulate the SOS response efficiently, maintaining a balance between repression and activation depending on the presence or absence of DNA damage.

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Key Concepts

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

SOS Response

The SOS response is a cellular mechanism in bacteria, particularly in Escherichia coli, that is activated in response to DNA damage. This response involves the expression of a set of genes that help repair damaged DNA and ensure cell survival. The SOS regulon includes various genes, including those regulated by the lexA protein, which plays a crucial role in controlling this response.

lexA Gene

The lexA gene encodes a repressor protein that inhibits the expression of SOS response genes under normal conditions. When DNA damage occurs, the lexA protein is cleaved, leading to the derepression of these genes. This mechanism ensures that the cell can quickly respond to and repair DNA damage, which is vital for maintaining genomic integrity.

Constitutive Expression

Constitutive expression refers to the continuous production of a gene product, regardless of environmental conditions. In the case of the lexA gene, its constitutive expression ensures that the repressor is always available to regulate the SOS response. This allows for a rapid response to DNA damage, as the system is primed to activate repair mechanisms immediately when needed.

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Related Practice

Textbook Question

A regulon is a set of genes controlled bya. one type of regulator of transcription.b. two or more different alternative sigma proteins.c. many different types of promoters.d. glucose.

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Textbook Question

A regulon is a set of genes controlled by

a. One type of regulator of transcription

b. Two or more different alternative sigma proteins

c. Many different types of promoters

d. Glucose

742

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Textbook Question

What would occur if the repressor of an inducible operon were mutated so it could not bind the operator?

a. Irreversible binding of the repressor to the promoter

b. Reduced transcription of the operon's genes

c. Buildup of a substrate for the pathway controlled by the operon

d. Continuous transcription of the operon's genes

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Textbook Question

Explain why it makes sense for the lexA regulatory gene of the SOS regulon to be expressed constitutively.

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Textbook Question

The diagram shown here is a model of the gene regulatory circuit for light production by V. fischeri cells. The lux operon contains genes for luminescence (luxCDABE) and a gene, luxI, that encodes an enzyme that catalyzes the production of an inducer. This inducer easily moves back and forth across the plasma membrane and acts as a signaling molecule. The lux operon is never completely turned off. The luxR gene codes for the activator LuxR. The inducer can bind to LuxR, and when it does, the LuxR–inducer complex can bind to a regulatory site to activate transcription of the lux operon and inhibit transcription of luxR. Explain how this gene regulatory circuit accounts for bacteria emitting light only when they reach a high cell density.

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Textbook Question

The diagram shown here is a model of the gene regulatory circuit for light production by V. fischeri cells. The lux operon contains genes for luminescence (luxCDABE) and a gene, luxI, that encodes an enzyme that catalyzes the production of an inducer. This inducer easily moves back and forth across the plasma membrane and acts as a signaling molecule. The lux operon is never completely turned off. The luxR gene codes for the activator LuxR. The inducer can bind to LuxR, and when it does, the LuxR–inducer complex can bind to a regulatory site to activate transcription of the lux operon and inhibit transcription of luxR.

Explain how this gene regulatory circuit accounts for bacteria emitting light only when they reach a high cell density.

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Textbook Question

LuxR is allosterically regulated by the inducer molecule secreted by V. fischeri. What does it mean that LuxR is allosterically regulated?

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Textbook Question

LuxR is allosterically regulated by the inducer molecule secreted by V. fischeri.

What does it mean that LuxR is allosterically regulated?

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