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Questions and Answers
What defines hemifusion in the context of membrane interactions?
What defines hemifusion in the context of membrane interactions?
- Fusion of only the inner leaflets of the membranes. (correct)
- Fusion of both outer leaflets of the membranes.
- Partial fusion before complete membrane merging.
- Fusion of transmembrane proteins only.
Which role do transmembrane proteins play during the reconstruction of the nuclear envelope?
Which role do transmembrane proteins play during the reconstruction of the nuclear envelope?
- They remain in vesicles and assist in forming the nucleus. (correct)
- They facilitate chromatin formation.
- They fuse immediately with the outer leaflets.
- They are detached and recycled.
What initiates the fusion process between two membranes?
What initiates the fusion process between two membranes?
- Chemical signals released by the cell.
- Proximity of the membranes due to slight deformation.
- Interactions among transmembrane and associated proteins. (correct)
- Lipids interacting only.
What is the final outcome of the vesicle fusion during nuclear envelope reconstruction?
What is the final outcome of the vesicle fusion during nuclear envelope reconstruction?
What happens to associated proteins during mitosis?
What happens to associated proteins during mitosis?
In what way does chromatin contribute to nuclear envelope reconstruction?
In what way does chromatin contribute to nuclear envelope reconstruction?
During the fusion process of the membranes, what is primarily reduced?
During the fusion process of the membranes, what is primarily reduced?
Which statement correctly describes the process of vesicle fusion?
Which statement correctly describes the process of vesicle fusion?
Which aspect of nuclear envelope reconstruction ensures the formation of nuclear pores?
Which aspect of nuclear envelope reconstruction ensures the formation of nuclear pores?
What is a significant outcome of protein interactions during vesicle fusion?
What is a significant outcome of protein interactions during vesicle fusion?
What is primarily responsible for the transport of cargo proteins with nuclear localization sequences (NLS) into the nucleus?
What is primarily responsible for the transport of cargo proteins with nuclear localization sequences (NLS) into the nucleus?
How are nuclear pores formed in cells that do not undergo cell division?
How are nuclear pores formed in cells that do not undergo cell division?
Which sequence would be recognized by exportins to facilitate the export of proteins from the nucleus?
Which sequence would be recognized by exportins to facilitate the export of proteins from the nucleus?
What function does the nuclear pore complex (NPC) primarily serve?
What function does the nuclear pore complex (NPC) primarily serve?
What happens to proteins with both NLS and NES sequences in a cell?
What happens to proteins with both NLS and NES sequences in a cell?
Which component within the nuclear pore allows the transport of specific proteins from the cytoplasm into the nucleus?
Which component within the nuclear pore allows the transport of specific proteins from the cytoplasm into the nucleus?
Why might some proteins remain in the cytosol despite having a nuclear localization sequence (NLS)?
Why might some proteins remain in the cytosol despite having a nuclear localization sequence (NLS)?
In which type of cells are nuclear pores predominantly formed de novo?
In which type of cells are nuclear pores predominantly formed de novo?
What is the primary role of importins in the context of nuclear transport?
What is the primary role of importins in the context of nuclear transport?
Which of the following is true about the nuclear pore complex regarding macromolecule transport?
Which of the following is true about the nuclear pore complex regarding macromolecule transport?
What role does phosphorylation play in the availability of the Nuclear Localization Signal (NLS)?
What role does phosphorylation play in the availability of the Nuclear Localization Signal (NLS)?
How does the interaction between importin and NLS promote nuclear transport?
How does the interaction between importin and NLS promote nuclear transport?
What is the effect of GTP on monomeric G-proteins like RAN?
What is the effect of GTP on monomeric G-proteins like RAN?
What triggers the detachment of the cargo from exportin in the cytoplasm?
What triggers the detachment of the cargo from exportin in the cytoplasm?
What describes RAN in the context of nuclear transport?
What describes RAN in the context of nuclear transport?
Which statement best describes the relationship between the NLS and NES in protein transport?
Which statement best describes the relationship between the NLS and NES in protein transport?
In which compartment is RAN-GTP highly concentrated?
In which compartment is RAN-GTP highly concentrated?
What role do RAN-GEF and RAN-GAP play in the functionality of Ran?
What role do RAN-GEF and RAN-GAP play in the functionality of Ran?
What is the consequence of GTP hydrolysis by RAN during the transport process?
What is the consequence of GTP hydrolysis by RAN during the transport process?
Which modification can affect the presence of the NLS on a protein?
Which modification can affect the presence of the NLS on a protein?
How does the presence of Ran-GEF affect the nucleotide state of Ran?
How does the presence of Ran-GEF affect the nucleotide state of Ran?
How does ligand-receptor interaction initiate cellular responses and modifications?
How does ligand-receptor interaction initiate cellular responses and modifications?
In which compartment is Ran-GAP primarily found and what is its function?
In which compartment is Ran-GAP primarily found and what is its function?
What effect does the nucleotide binding state of Ran have on the binding to importin?
What effect does the nucleotide binding state of Ran have on the binding to importin?
What is the primary physiological consequence of Ran being associated with GTP?
What is the primary physiological consequence of Ran being associated with GTP?
What is the significance of the asymmetric distribution of Ran-GEF and Ran-GAP?
What is the significance of the asymmetric distribution of Ran-GEF and Ran-GAP?
Which characteristic of Ran-GEF allows it to effectively promote nucleotide exchange?
Which characteristic of Ran-GEF allows it to effectively promote nucleotide exchange?
What happens to Ran-GTP when it interacts with Ran-GAP?
What happens to Ran-GTP when it interacts with Ran-GAP?
Why does Ran prefer to associate with GDP as opposed to GTP?
Why does Ran prefer to associate with GDP as opposed to GTP?
What key function does Ran-GTP perform in relation to exportin?
What key function does Ran-GTP perform in relation to exportin?
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Study Notes
Nuclear Pore Complex (NPC) Dynamics
- NPC facilitates protein and ribonucleoprotein transport between cytoplasm and nucleus, functioning as a selective, bidirectional transporter.
- Transmembrane proteins interact, allowing two membranes to come closer for fusion, leading to the formation of the nuclear envelope and nuclear pores.
- Hemifusion initiates with fusion of the inner leaflets of membranes before resulting in the full fusion, establishing a passage.
Protein Transport Mechanisms
- Import involves transporting proteins with nuclear localization sequences (NLS) from the cytoplasm to the nucleus.
- Karyopherins, notably importins, are responsible for transporting proteins through NPC by recognizing NLS.
- Proteins can have dual functionality, containing both NLS for import and nuclear export sequences (NES) for export through exportins.
Export and Regulation
- Export from the nucleus to the cytoplasm requires NES and involves exportin proteins.
- Proteins may shuttle between the nucleus and cytoplasm, influenced by their NLS or NES based on functional needs.
- The availability of NLS can be regulated through protein-protein interactions or post-translational modifications such as phosphorylation, impacting protein localization.
Role of Monomeric G-Proteins in Transport
- RAN, a monomeric G-protein, regulates transportation across NPC by switching between GTP-bound (active) and GDP-bound (inactive) states.
- High concentration of RAN-GTP is found in the nucleus, whereas RAN-GDP predominates in the cytoplasm due to GTPase activity.
- Interaction with guanosine exchange factor (Ran-GEF) in the nucleus promotes nucleotide exchange from GDP to GTP.
Mechanism of Cargo Detachment
- GTP hydrolysis regulated by Ran-GAP promotes cargo release from importins and exportins during transport.
- The different concentrations of Ran-GAP (higher in cytoplasm) and Ran-GEF (higher in nucleus) drive the regulation of import/export processes.
Summary of Import/Export Process
- Import: Proteins with NLS bind to importins in the cytoplasm, transport to nucleus, detach in nucleus due to RAN-GTP.
- Export: Proteins with NES bind exportins in the nucleus, convert to GDP-bound RAN in cytoplasm causing detachment.
- GTPase activity of RAN critically controls the cycle of protein transport across the nuclear envelope.
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