Protein Sorting at the Cytoplasm Quiz

12 Questions

What is the function of nuclear pore complexes (NPCs) in the nuclear envelope?

Facilitate the translocation of proteins into and out of the nucleus

What type of proteins are directed into the nucleus?

Proteins with a nuclear localization sequence (NLS)

What is the role of import receptors (importins) in protein translocation?

Contain multiple low-affinity binding sites for the FG repeats found in the unstructured domains of nucleoporins

What characterizes proteins with a nuclear export sequence (NES)?

They leave the nucleus

Which complex locally dissolves the gel-like mesh and can diffuse into and within the NPC pore?

Importin–cargo complex

What promotes cargo dissociation for importins in the nucleus?

Ran-GTP

What triggers GTP hydrolysis for Ran-GDP?

GTPase-activating protein (GAP)

What do exportins promote in the nucleus?

Cargo binding

Which subunit of importin binds the nuclear localization signal (NLS)?

α subunit

What prevents mitochondrial proteins from folding in the cytoplasm?

Hsp-70 chaperones

Which systems move polypeptide chains through the two membranes of the mitochondria?

TIM and TOM

What do exportins bind to guide their cargo to the cytosol?

Export signal and NPC proteins

Study Notes

Nuclear Pore Complexes (NPCs)

Function to transport molecules between the nucleus and cytoplasm.

Protein Transport

Proteins with a nuclear localization signal (NLS) are directed into the nucleus.
Import receptors (importins) bind to these proteins and mediate their transport into the nucleus.

Importin Function

Import receptors (importins) bind to proteins with a nuclear localization signal (NLS) and facilitate their transport into the nucleus.

Nuclear Export Sequence (NES)

Characterized by proteins that are exported from the nucleus to the cytoplasm.
Proteins with a NES are recognized by exportins, which facilitate their export from the nucleus.

Translocation through NPC

The FG-Nup complex locally dissolves the gel-like mesh and can diffuse into and within the NPC pore.

Importin-Cargo Dissociation

Ran-GTP promotes cargo dissociation for importins in the nucleus.

Ran-GTP Hydrolysis

Triggered by the binding of Ran-GTP to importin, causing a conformational change that triggers GTP hydrolysis.

Exportin Function

Exportins bind to proteins with a NES and promote their export from the nucleus to the cytosol.

Importin Subunit

The α subunit of importin binds the nuclear localization signal (NLS) of proteins.

Mitochondrial Protein Folding

Chaperone proteins prevent mitochondrial proteins from folding in the cytoplasm, ensuring proper targeting to the mitochondria.

Mitochondrial Protein Transport

The TIM23 and TOM complexes move polypeptide chains through the two membranes of the mitochondria.

Exportin-Cargo Binding

Exportins bind to proteins with a NES, guiding their cargo to the cytosol.