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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1:47 minutes

Problem 2

Textbook Question

In the lac operon, the repressor inhibits transcription when
a. The repressor is bound to the inducer.
b. The repressor is not bound to the inducer.
c. The repressor is bound to glucose.
d. The repressor is not bound to the operator.

Verified step by step guidance

Understand the role of the lac operon: It is a set of genes involved in lactose metabolism in E. coli, regulated by the presence or absence of lactose.

Identify the components of the lac operon: The operon includes the promoter, operator, and structural genes (lacZ, lacY, and lacA). The repressor protein is encoded by the lacI gene.

Recognize the function of the repressor: The repressor binds to the operator region to block RNA polymerase from transcribing the structural genes when lactose is absent.

Determine the effect of the inducer: The inducer (allolactose, a derivative of lactose) binds to the repressor, causing a conformational change that prevents the repressor from binding to the operator.

Analyze the given options: The repressor inhibits transcription when it is bound to the operator, which occurs when the inducer is not present. Therefore, the correct condition is when the repressor is not bound to the inducer.

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Key Concepts

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

Lac Operon

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It includes structural genes, a promoter, an operator, and a repressor. The operon is a classic example of gene regulation, where the presence or absence of lactose influences the transcription of these genes.

Repressor Protein

The repressor protein in the lac operon binds to the operator region to inhibit transcription. When lactose is absent, the repressor binds to the operator, preventing RNA polymerase from transcribing the genes. When lactose is present, it binds to the repressor, causing a conformational change that releases the operator, allowing transcription.

Inducer

An inducer is a molecule that initiates gene expression. In the lac operon, allolactose acts as an inducer by binding to the repressor protein, altering its shape, and preventing it from binding to the operator. This allows RNA polymerase to access the promoter and transcribe the genes necessary for lactose metabolism.