Lecture 13: Cell bio Protein Sorting in Eukaryotic CellL

The process of directing proteins to specific organelles within a eukaryotic cell.

A short amino acid sequence in a protein that directs its import into a specific organelle.

Different ways proteins are delivered to organelles. Typically, the mechanism involves recognition of a signal sequence by an organelle.

Organelles importing proteins to perform their specific functions.

Signal sequences contain specific amino acid sequences (rich in hydrophobic, basic, or alternating hydrophobic amino acids) which aid in targeting. These features may be present at the N-terminus, C-terminus or anywhere in the protein.

Proteins enter peroxisomes in a folded state, unlike mitochondria where they must unfold.

A receptor binds to the signal sequence (SKL) on the protein and escorts it into the peroxisome. The receptor is then recycled back to the cytosol.

The SKL signal sequence is recognized by the receptor but is not cleaved off once the protein reaches the peroxisome.

Energy (ATP) is required for the receptor to return to the cytosol, allowing it to pick up new cargo.

Catalase, normally found in peroxisomes, is likely localized in the cytosol of cells lacking peroxisomes. It is a soluble protein and would be in the default location if not targeted to an organelle.

A complex channel embedded in the nuclear envelope that allows the transport of molecules between the nucleus and cytoplasm.

The process by which proteins and other molecules are transported through nuclear pores into or out of the nucleus.

Proteins enter the nucleus through nuclear pores in their fully folded state, either by passive diffusion for small proteins or active transport for larger proteins.

A specific amino acid sequence on a protein that signals its transport into the nucleus.

A protein that binds to the NLS on cargo proteins and facilitates their transport through nuclear pores.

A small GTPase protein that plays a crucial role in the directionality of nuclear transport by binding to import receptors and cargo.

Ran-GTP promotes the release of cargo from the import receptor inside the nucleus, ensuring unidirectional movement.

The process of moving proteins and other molecules out of the nucleus. This involves a similar mechanism to nuclear import but operates in reverse.

The process of transporting proteins from the cytosol into the mitochondria, where they perform specific functions.

A protein complex located in the outer membrane of mitochondria that acts as a gatekeeper for proteins entering the organelle.

A protein complex in the inner mitochondrial membrane that collaborates with the TOM complex to guide proteins into the mitochondrial matrix.

A specific type of signal sequence crucial for protein import into the mitochondria, rich in positively charged amino acids.

A protein complex in the inner mitochondrial membrane that helps insert transmembrane proteins into the inner membrane.

A protein complex embedded in the outer mitochondrial membrane responsible for inserting porins into the outer membrane.

Peroxisomes break down fatty acids and toxins, and produce hydrogen peroxide which is then broken down by catalase.

A transcription factor that regulates the immune response to infection. It is usually inactive in the cytosol, bound to IκB.

A protein that binds to NF-κB, preventing its nuclear localization signal (NLS) from being exposed and inhibiting its activation.

The process of attaching ubiquitin molecules to a protein, targeting it for degradation by proteasomes. In the case of IκB, its ubiquitination leads to its degradation, releasing NF-κB.

A process where one organism lives inside another organism, with both benefiting from the relationship. This is believed to be the origin of mitochondria and chloroplasts.

A type of helix in a protein that has both hydrophobic and hydrophilic regions. It is often involved in membrane interactions.

The process by which proteins are imported into mitochondria. It involves a specific signal sequence and a series of translocation channels in the mitochondrial membranes.