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

10. Cell Signaling

Introduction to Cell Signaling

General Biology

10. Cell Signaling

Introduction to Cell Signaling

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Multiple Choice

Why doesn't a skin cell produce crystallin protein, which is abundant in lens cells of the eye?

Skin cells do not have ribosomes to synthesize crystallin protein.

The crystallin gene is not expressed in skin cells due to differences in gene regulation.

Skin cells lack the DNA sequence for the crystallin gene.

Crystallin protein is toxic to skin cells, so it is actively degraded.

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Verified step by step guidance

Understand the problem: The question is asking why skin cells do not produce crystallin protein, which is abundant in lens cells of the eye. The options provided suggest different reasons, and we need to evaluate them based on biological principles.

Step 1: Recall the concept of gene expression. All cells in an organism contain the same DNA, but different cell types express different sets of genes. This is due to gene regulation, which determines which genes are turned on or off in a specific cell type.

Step 2: Evaluate the first option: 'Skin cells do not have ribosomes to synthesize crystallin protein.' This is incorrect because all cells, including skin cells, have ribosomes to synthesize proteins. Ribosomes are essential for protein synthesis in all cell types.

Step 3: Evaluate the second option: 'The crystallin gene is not expressed in skin cells due to differences in gene regulation.' This is correct because gene regulation ensures that only the genes necessary for a specific cell type's function are expressed. In skin cells, the crystallin gene is not activated, so the protein is not produced.

Step 4: Evaluate the remaining options: 'Skin cells lack the DNA sequence for the crystallin gene' is incorrect because all cells in the body have the same DNA. 'Crystallin protein is toxic to skin cells, so it is actively degraded' is also incorrect because there is no evidence that crystallin protein is toxic to skin cells. The correct answer is based on gene regulation.