Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

2. Cell Chemistry & Cell Components

Endomembrane System: Protein Secretion

Anatomy & Physiology

2. Cell Chemistry & Cell Components

Endomembrane System: Protein Secretion

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0:51 minutes

Problem 7

Textbook Question

Most of the proteins that enter the nucleus possess a nuclear localization signal (NLS), even if they are small enough to pass through the nuclear pore complex unhindered. Why would a small protein have an NLS, when it naturally diffuses across the nuclear pore complex without one?

Verified step by step guidance

Understand the function of the nuclear localization signal (NLS): The NLS is a sequence of amino acids that acts as a 'tag' directing the protein to the nucleus.

Recognize the role of the nuclear pore complex (NPC): The NPC regulates the transport of molecules between the nucleus and the cytoplasm, allowing passive diffusion of small molecules and active transport of larger ones.

Consider the efficiency of transport: Even though small proteins can diffuse passively, having an NLS ensures that they are actively and efficiently transported into the nucleus, which is crucial for timely cellular processes.

Acknowledge the specificity of transport: The NLS ensures that proteins are specifically recognized and transported to the nucleus, preventing them from diffusing to other cellular compartments where they might be non-functional or harmful.

Reflect on the regulation of nuclear import: The presence of an NLS allows the cell to regulate the import of proteins into the nucleus, which can be important for controlling gene expression and other nuclear functions.

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Key Concepts

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

Nuclear Localization Signal (NLS)

A Nuclear Localization Signal (NLS) is a specific amino acid sequence that directs proteins to the nucleus. It is recognized by nuclear transport receptors, facilitating the active transport of proteins through the nuclear pore complex. Even small proteins that can diffuse through the pore may have an NLS to ensure their proper localization and function within the nucleus.

Nuclear Pore Complex (NPC)

The Nuclear Pore Complex (NPC) is a large protein structure that spans the nuclear envelope, regulating the transport of molecules between the nucleus and the cytoplasm. It allows passive diffusion of small molecules but requires active transport mechanisms for larger proteins. The presence of an NLS is crucial for proteins that need to be selectively imported into the nucleus, ensuring they reach their destination efficiently.

Protein Function and Localization

Protein function is often closely tied to its localization within the cell. Proteins that operate in the nucleus typically perform roles in gene expression, DNA replication, or repair. Having an NLS, even for small proteins, ensures that they are correctly localized to the nucleus, where they can interact with other nuclear components and fulfill their biological roles effectively.