Cell Biology Protein Import Quiz

The process of delivering proteins to the correct organelles within a eukaryotic cell.

Short amino acid sequences within a protein that act as a 'postal code' directing the protein to its target organelle.

Different ways proteins are transported to their target organelles, including unidirectional and bidirectional transport.

Characteristics of the amino acid sequences within proteins that define their target organelles.

Proteins lacking a signal sequence often get degraded, or their location depends on the context.

Nuclear pores are the gateways for protein movement between the nucleus and cytoplasm.

A specific amino acid sequence on a protein that directs it to the nucleus.

Process by which proteins enter the nucleus.

Protein that binds to NLS and helps transport proteins into the nucleus.

A protein that provides energy for nuclear transport by cycling between different forms.

Method of separation of molecules from their size, the nuclear pore selectively transports proteins and structures based on size.

Process by which proteins exit the nucleus.

Proteins enter and leave the nucleus through nuclear pores, either by size exclusion or active transport.

NFκB is a protein that helps our immune system fight infections. Normally, it's held inactive in the cytoplasm by IκB. During infections, IκB breaks down, releasing NFκB. This allows NFκB to enter the nucleus and activate genes to fight the infection.

For NFκB to activate genes, it needs to move into the nucleus. This movement is called nuclear localization.

Anything that prevents NFκB from entering the nucleus will decrease its nuclear localization. This includes factors like IκB binding, mutations in the NLS, and disruptions to the nuclear import machinery.

A short stretch of amino acids at the beginning of a protein that acts as a 'zip code' directing it to the mitochondria.

The signal sequence for mitochondrial import is an amphipathic α-helix. One side of the helix has positively charged residues, and the other side has hydrophobic residues.

Proteins destined for the mitochondria must be unfolded before they can be imported. This is done through a complex of proteins that act as a 'translocon'.

The idea that mitochondria and chloroplasts were once free-living bacteria that were engulfed by early eukaryotic cells and eventually became essential organelles.

There are several steps involved in the transition from a free-living endosymbiont to an organelle. These include: transfer of genes to the host nucleus, evolution of translocators and signal sequences, loss of essential genes from the endosymbiont, and reduction of the endosymbiont genome.

Soluble proteins are imported into peroxisomes in their folded state, unlike mitochondrial import where proteins must unfold.

Peroxisome import shares similarities with nuclear import in its use of a receptor (R) that recognizes specific signals on cargo proteins.

Peroxisome import resembles mitochondrial import in its requirement for ATP hydrolysis during translocation.

In cells lacking peroxisomes, catalase, a peroxisomal enzyme, is likely located in the cytosol or other compartments.

In normal cells, catalase appears as small dots because individual peroxisomes are scattered within the cell.

The TOM complex (Translocator of the Outer Membrane) and TIM complex (Translocator of the Inner Membrane) work together to import proteins into the mitochondrial matrix. The TOM complex receives proteins with signal sequences, guides them through the outer membrane, and then interacts with the TIM complex to thread the protein across the inner membrane into the matrix.

A specific short amino acid sequence at the N-terminus of a protein that targets it to the mitochondria. It acts like a 'zip code' directing the protein to the correct organelle for import.

Protein import into the mitochondria is an active process, meaning it requires energy. This energy is necessary to move proteins against their concentration gradient and across the mitochondrial membranes.

The mitochondrial signal sequence is typically characterized by a hydrophobic stretch of amino acids. This hydrophobic nature allows the signal sequence to interact with the TOM complex and initiate protein transport across the membrane.

Mutations in the signal sequence can hinder the transport of proteins to the mitochondria. Changing charged amino acids to acidic ones, or altering hydrophobic residues, can disrupt the signal sequence's ability to interact with the TOM complex and properly target the protein.

Peroxisomes are small organelles responsible for carrying out oxidation reactions, producing hydrogen peroxide as a byproduct. They bud off from the ER and divide by fission, receiving both membrane and matrix proteins from various sources, including the ER and cytosol.

Peroxisomes play a crucial role in various metabolic processes, including lipid metabolism, detoxification of harmful substances, and breakdown of specific molecules. They contain enzymes like catalase, which breaks down hydrogen peroxide.

Peroxisomes are characterized by electron-dense cores visible under electron microscopy. These cores are formed by the crystallization of some of their enzymes, such as catalase and urate oxidase, during the preparation process.