Term
| What is the nuclear envelope? |
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Definition
| - boundary between the cytosol and nucleus |
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Term
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Definition
| - "doorways" in the nuclear envelope |
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Term
| What are the two main functions of the nucleus? |
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Definition
1. compartmentalization of cellular genome and activities
2. coordination of cellular activities |
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Term
| What is included in the nuclear envelope? |
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Definition
1. nuclear membrane
2. nuclear lamina
3. nuclear pores |
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Term
| What is included in the nuclear content? |
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Definition
1. chromatin
2. nucleoplasm
3. nuclear matrix
4. nucleolus |
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Term
| What are the three domains of the nucleus? |
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Definition
1. outer membrane
2. inner membrane
3. intermembrane space |
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Term
| What occurs at the outer membrane? |
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Definition
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Term
| What is the outer membrane continuous with? |
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Definition
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Term
| What important structures does the inner membrane contain? |
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Definition
| - integral membrane proteins that connect the nuclear lamina |
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Term
| What is the intermembrane space continuous with? |
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Definition
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Term
| What are the functions of the nuclear envelope? |
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Definition
1. separates nuclear content from cytoplasm
2. acts as a selective barrier
3. binds nuclear lamina |
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Term
| Explain how the nuclear envelope acts as a selective barrier? |
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Definition
| - allows regulated passage of molecules between the nucleus and cytosol |
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Term
| Describe the structure of the nuclear lamina |
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Definition
| - thin meshwork of long filament-like proteins |
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Term
| Where is the nuclear lamina located? |
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Definition
| - bound to the inner surface of the nuclear envelope |
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Term
| What are the functions of the nuclear lamina? |
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Definition
1. support structure for nuclear envelope
2. scaffold for chromatin and nuclear matrix attachment |
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Term
| What are nuclear pore complexes (NPCs)? |
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Definition
- protein structures that fill nuclear pores
- made up of nucleoporins (NUPs) |
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Term
| Describe the structure of a nuclear pore complex. |
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Definition
- octagonal symmetry organized around a large channel
- central scaffold anchors complex to nuclear envelope |
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Term
| What is the inner surface of the NPC channel lined with? |
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Definition
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Term
| What do the FG domains form? |
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Definition
| - form a hydrophobic "mesh" that limits diffusion of large macromolecules (>30nm diameter) |
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Term
| What are the main structures involved in nuclear receptor-cargo protein recognition and import? |
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Definition
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Term
| What are the 2 major functions of nuclear pore complexes? |
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Definition
1. passive diffusion of small molecules
2. to regulate movement of larger molecules |
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Term
| What is a nuclear localization signal (NLS)? |
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Definition
| - specific stretch of AA's that are recognized by nuclear receptor proteins |
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Term
| Why is a nuclear localization signal needed? |
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Definition
| - serves as a zip code to mediate targeting of protein from cytosol to nucleus |
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Term
| What is the difference between a classic NLS and a bipartite NLS? |
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Definition
- classic: consist of a short stretch of basic AA
- bipartite: composed of two short basic AA sequences with a spacer sequence in between |
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Term
| What are other proteins that are necessary for nucleoplasmic transport? |
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Definition
- transport proteins aka karyoferins
- small GTP-binding proteins (ex. Ran) |
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Term
| Outline step 1 of nuclear import. |
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Definition
1. nascent NLS-containing cargo proteins are recognized by importin alpha and beta
2. importin alpha recognizes and binds to the basic residues in the NLS |
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Term
| Outline step 2 in nuclear import. |
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Definition
1. cargo protein-importin complex moves through the cytosol towards nucleus
2. at surface of nucleus, importin beta binds to a cytoplasmic filament at the NPC |
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Term
| Outline step 3 in nuclear import. |
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Definition
1. complex is translocated through aqueous central channel of NPC
2. interacts with FG domains of the NUPS in the central channel
3. interaction dissolves the domain network and allows translocation |
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Term
| Outline step 4 in nuclear transport. |
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Definition
1. complex associates with nuclear basket on inner surface of NPC
2. binds to active Ran-GTP (via importin beta) and results in release from NPC and disassembly into nucleoplasm |
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Term
| Outline the first part of step 5 of nuclear import. |
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Definition
1. Ran-GTP and importin beta moves back to cytosol due to low cytosolic [Ran-GTP]
2. in the cytosol, GTP is hydrolyzed (via GAP1) to GDP
3. Ran-GDP is released from importin beta
4. Ran-GDP moves back into the nucleus due to low nuclear [Ran-GDP] gradient
4. GDP converted back to Ran-GTP by RCC1 |
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Term
| Outline the second part of step 5 in nuclear import. |
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Definition
1. importin alpha binds to exportin
2. complex binds Ran-GTP
3. full complex is transported into cytosol due to [Ran-GTP] gradient
4. in the cytosol, GAP1 hydrolyzes GTP to GDP
5. Ran-GDP is released from export in, causes release of importin alpha
6. Ran-GDP moves back into nucleus and is converted to GTP by RCC1
7. exportin also moves back into nucleus |
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Term
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Definition
| - some proteins lack an NLS so they bind to a protein that DOES contain an NLS and piggybacks into the nucleus |
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Term
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Definition
- highly organized
- fluid-filled interior of the nucleus
- consists of >30 specialized regions with specific functions |
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Term
| What is the nuclear matrix? |
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Definition
- insoluble fibrillar-like protein network
- distributed throughout the nucleoplasm |
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Term
| What are the functions of the nuclear matrix? |
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Definition
1. structure - maintain overall 3D structure of nucleus
2. scaffold - organizing nuclear subdomains |
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Term
| What are nuclear speckles? |
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Definition
| - subdomains where mRNA splicing factors are concentrated |
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Term
| The size and number of nucleoli depend on what? |
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Definition
| - metabolic activity of the cell |
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Term
| What is the main function of the nucleolus? |
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Definition
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