Perroteau - L8 cont

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Questions and Answers

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?

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?

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?

Creation of nuclear pores in the envelope. Signup and view all the answers

What happens to associated proteins during mitosis?

They detach from the membranes. Signup and view all the answers

In what way does chromatin contribute to nuclear envelope reconstruction?

By associating with lamin proteins and vesicles. Signup and view all the answers

During the fusion process of the membranes, what is primarily reduced?

The interaction distance between the two membranes. Signup and view all the answers

Which statement correctly describes the process of vesicle fusion?

It involves interactions of proteins leading to membrane distortion. Signup and view all the answers

Which aspect of nuclear envelope reconstruction ensures the formation of nuclear pores?

The sequential fusion of inner leaflets leading to pore creation. Signup and view all the answers

What is a significant outcome of protein interactions during vesicle fusion?

The start of hemifusion between internal membranes. Signup and view all the answers

What is primarily responsible for the transport of cargo proteins with nuclear localization sequences (NLS) into the nucleus?

Karyopherins Signup and view all the answers

How are nuclear pores formed in cells that do not undergo cell division?

They are created de novo. Signup and view all the answers

Which sequence would be recognized by exportins to facilitate the export of proteins from the nucleus?

Nuclear Export Localization Sequence (NES) Signup and view all the answers

What function does the nuclear pore complex (NPC) primarily serve?

It serves as a bidirectional transporter for macromolecules. Signup and view all the answers

What happens to proteins with both NLS and NES sequences in a cell?

They shuttle between the nucleus and cytoplasm. Signup and view all the answers

Which component within the nuclear pore allows the transport of specific proteins from the cytoplasm into the nucleus?

Fibers proteins outside the nuclear pore Signup and view all the answers

Why might some proteins remain in the cytosol despite having a nuclear localization sequence (NLS)?

Post-translational modifications can prevent their transport. Signup and view all the answers

In which type of cells are nuclear pores predominantly formed de novo?

Neuronal cells Signup and view all the answers

What is the primary role of importins in the context of nuclear transport?

To facilitate the entry of proteins into the nucleus Signup and view all the answers

Which of the following is true about the nuclear pore complex regarding macromolecule transport?

It selectively transports proteins and ribonucleoproteins. Signup and view all the answers

What role does phosphorylation play in the availability of the Nuclear Localization Signal (NLS)?

Phosphorylation introduces a negative charge that may change the shape, making the NLS available. Signup and view all the answers

How does the interaction between importin and NLS promote nuclear transport?

Importin carries the cargo protein through nuclear pores into the nucleus. Signup and view all the answers

What is the effect of GTP on monomeric G-proteins like RAN?

GTP binding activates the RAN monomeric G-protein. Signup and view all the answers

What triggers the detachment of the cargo from exportin in the cytoplasm?

Unique regulatory proteins that facilitate detachment mechanisms. Signup and view all the answers

What describes RAN in the context of nuclear transport?

RAN is a monomeric G-protein that is activated by GTP binding. Signup and view all the answers

Which statement best describes the relationship between the NLS and NES in protein transport?

NLS signals the import while NES signals the export of proteins. Signup and view all the answers

In which compartment is RAN-GTP highly concentrated?

In the nucleus. Signup and view all the answers

What role do RAN-GEF and RAN-GAP play in the functionality of Ran?

They facilitate nucleotide exchange and hydrolysis of GTP. Signup and view all the answers

What is the consequence of GTP hydrolysis by RAN during the transport process?

It converts RAN-GTP to RAN-GDP, regulating transport efficiency. Signup and view all the answers

Which modification can affect the presence of the NLS on a protein?

Phosphorylation that changes protein configuration. Signup and view all the answers

How does the presence of Ran-GEF affect the nucleotide state of Ran?

It facilitates the conversion of Ran-GDP into Ran-GTP. Signup and view all the answers

How does ligand-receptor interaction initiate cellular responses and modifications?

Receptor activation leads to a cascade of intracellular signals. Signup and view all the answers

In which compartment is Ran-GAP primarily found and what is its function?

In the cytoplasm; it activates hydrolysis of GTP to GDP. Signup and view all the answers

What effect does the nucleotide binding state of Ran have on the binding to importin?

Ran-GTP promotes dissociation of the cargo from importin. Signup and view all the answers

What is the primary physiological consequence of Ran being associated with GTP?

The structural conformation of Ran changes, increasing its energy state. Signup and view all the answers

What is the significance of the asymmetric distribution of Ran-GEF and Ran-GAP?

It regulates the activity of Ran by influencing the nucleotide exchange dynamics. Signup and view all the answers

Which characteristic of Ran-GEF allows it to effectively promote nucleotide exchange?

It associates with chromatin in the nucleus. Signup and view all the answers

What happens to Ran-GTP when it interacts with Ran-GAP?

It undergoes hydrolysis to become Ran-GDP. Signup and view all the answers

Why does Ran prefer to associate with GDP as opposed to GTP?

GDP results in a more stable, lower energy state for Ran. Signup and view all the answers

What key function does Ran-GTP perform in relation to exportin?

It enhances the affinity of exportin for its cargo. Signup and view all the answers

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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Description

This quiz explores the dynamic nature of nucleoporins and their interactions within cellular membranes. It discusses how transmembrane proteins facilitate the proximity of outer and inner membranes, detailing the changes that occur during these interactions. Test your understanding of the processes behind nucleocytoplasmic transport.