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

5. Cell Components

Endomembrane System: Protein Secretion

General Biology

5. Cell Components

Endomembrane System: Protein Secretion

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3:01 minutes

Problem 2

Textbook Question

Which of the following results provided evidence of a discrete nuclear localization signal somewhere on the nucleoplasmin protein?
a. The nucleoplasmin protein was small and easily slipped through the nuclear pore complex.
b. After cleavage of the nucleoplasmin protein, only the tail segments appeared in the nucleus.
c. Removing the tail from the nucleoplasmin protein allowed the core segment to enter the nucleus.
d. The SRP bound only to the tail of the nucleoplasmin protein, not the core segment.

Verified step by step guidance

Understand the concept of a nuclear localization signal (NLS): A nuclear localization signal is a sequence of amino acids that 'tags' a protein for import into the cell nucleus by nuclear transport. Proteins with an NLS can be recognized by nuclear transport receptors and transported through the nuclear pore complex.

Analyze the options provided: Each option describes a different experimental observation related to the nucleoplasmin protein. The goal is to identify which observation suggests the presence of a discrete NLS on the protein.

Consider option b: 'After cleavage of the nucleoplasmin protein, only the tail segments appeared in the nucleus.' This suggests that the tail segments contain the NLS, as they are the only parts of the protein that enter the nucleus after cleavage.

Evaluate the significance of option b: The fact that only the tail segments appear in the nucleus after cleavage indicates that these segments have the necessary signal for nuclear entry, providing evidence of a discrete NLS located on the tail.

Conclude the analysis: Based on the evidence provided by option b, the presence of a discrete nuclear localization signal on the nucleoplasmin protein is supported by the observation that the tail segments, which contain the NLS, are able to enter the nucleus.

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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 sequence of amino acids that 'tags' a protein for import into the cell nucleus by nuclear transport. Proteins with an NLS are recognized by nuclear transport receptors, which facilitate their passage through the nuclear pore complex. Understanding NLS is crucial for identifying how proteins are selectively transported into the nucleus.

Nucleoplasmin Protein Structure

Nucleoplasmin is a pentameric protein involved in chromatin assembly and is known for its role in nuclear transport. It consists of distinct segments, typically a core and a tail, each potentially having different functions or signals. The structure of nucleoplasmin is essential for understanding how its segments contribute to its localization and function within the cell.

Nuclear Pore Complex (NPC)

The Nuclear Pore Complex (NPC) is a large protein complex that spans the nuclear envelope, acting as a gateway for the transport of molecules between the nucleus and the cytoplasm. It allows the passage of small molecules by passive diffusion, while larger molecules require active transport facilitated by signals like the NLS. Understanding NPC function is key to comprehending how proteins like nucleoplasmin are transported into the nucleus.

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Related Practice

Multiple Choice

Consider a protein that is made in the rough endoplasmic reticulum. You observe that when the synthesis of the protein is completed, the protein is located in the ER membrane. Where else in the cell might this protein be found?

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Multiple Choice

A protein that ultimately functions in the plasma membrane of a cell is most likely to have been synthesized __________.

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Textbook Question

Which structure is part of the endomembrane system?

a. Mitochondrion

b. Golgi apparatus

c. Chloroplast

d. Centrosome

Which structure is not part of the endomembrane system?

a. Nuclear envelope

b. Chloroplast

c. Golgi apparatus

d. Plasma membrane

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Textbook Question

Molecular zip codes direct molecules to particular destinations in the cell. How are these signals read?

a. They bind to receptor proteins.

b. They enter transport vesicles.

c. They bind to motor proteins.

d. They are glycosylated by enzymes.

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Textbook Question

Cells that line your intestines are known to possess a large number of membrane proteins that transport small molecules and ions across the plasma membrane. Which of the following cell structures would you expect to be required for this characteristic of the cells?

a. The endoplasmic reticulum

b. Peroxisomes

c. Lysosomes

d. The cell wall

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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?

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Textbook Question

In which cell would you find the most smooth ER?

a. Pancreatic cell that secretes digestive enzymes

b. Ovarian cell that produces estrogen (a steroid hormone)

c. Muscle cell in the thigh of a long-distance runner

d. White blood cell that engulfs bacteria

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