Questions and Answers
Which molecules do not normally cross the nuclear membrane?
DNA
The nuclear envelope is continuous with the Golgi apparatus.
False
Large proteins containing a nuclear localization signal (NLS) bind to the nuclear pore and enter the nucleus without any expenditure of energy.
False
What type of transport occurs when a small protein (molecular weight = 25,000 daltons) is injected into a cell and observed in the nucleus a short time later?
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In experiments to test whether a protein can enter the nucleus, why would proteins be labeled with fluorescent molecules?
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What conclusion can be drawn if one fusion protein is found in the nucleus and the other in the cytoplasm?
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Study Notes
Transport into the Nucleus
- DNA remains within the nucleus; it does not cross the nuclear membrane, which isolates processes involving genetic material.
- The nuclear envelope is not continuous with the Golgi apparatus; it is instead continuous with the endoplasmic reticulum, playing a key role in cellular logistics.
- Large proteins with a nuclear localization signal (NLS) do not enter the nucleus autonomously. Importins, a type of cytoplasmic protein, facilitate their transport via an energy-dependent active transport mechanism through nuclear pores.
- Small proteins, such as those weighing 25,000 daltons or less, can undergo passive transport. These proteins can diffuse through nuclear pores without needing energy.
- Fluorescent labeling of proteins provides visual confirmation of their location within a cell, facilitating experimentation to determine nuclear entry capabilities.
- In experiments involving nucleoplasmin, only one of the two fusion proteins created (one injected into the cell) contained a nuclear localization signal. This indicates that NLS presence is critical for proteins to be successfully transported to the nucleus.
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Description
Test your knowledge about nuclear transport processes with this set of flashcards. Learn important facts about what molecules cross the nuclear membrane and the structure of the nuclear envelope. Perfect for students studying cell biology and genetics.
