Intracellular Organization and Protein Sorting

According to the data for a typical liver cell (hepatocyte), which intracellular compartment occupies approximately 22 percent of the total cell volume?

In a pancreatic exocrine cell, which is specialized for secretion, the rough ER membrane constitutes what percentage of the total cell membrane?

What are the three distinct families of intracellular compartments in eukaryotic cells, based on their topological relationships and origins?

What is the primary characteristic of the central scaffolding component of the nucleolus?

What is the term for the transport mechanism where proteins move between the cytosol and the nucleus through nuclear pore complexes?

An ER signal sequence, which directs a protein to the ER, typically contains a linear sequence of about how many predominantly hydrophobic amino acids?

What happens to the signal-recognition particle (SRP) and SRP receptor after they deliver an SRP–ribosome complex to an unoccupied protein translocator in the ER membrane?

What is the function of the lateral gate, or seam, in the Sec61 protein translocator?

How are tail-anchored proteins, which have a single transmembrane helix very close to their C-terminus, inserted into the ER membrane?

What is the role of the ER resident protein BiP in post-translational translocation into the ER?

The ER-resident chaperones calnexin and calreticulin are lectins that play a key role in protein folding. What specific feature do they recognize on incompletely folded proteins?

What is the primary trigger for initiating the Unfolded Protein Response (UPR) in a cell?

The IRE1 pathway, a limb of the Unfolded Protein Response, involves a unique molecular event to produce an active transcription regulatory protein. What is this event?

Where in the cell does the synthesis of phospholipids, such as phosphatidylcholine, occur?

What is the function of the enzyme scramblase in the ER membrane?

Zellweger syndrome is a human disease caused by mutations that impair peroxisomal protein import, leading to 'empty' peroxisomes. What is the metabolic consequence of this defect?

What are the names of the multisubunit protein translocator complexes located in the outer and inner mitochondrial membranes, respectively?

Protein import into the mitochondrial matrix space requires energy from multiple sources. Which of the following is NOT a source of energy for this process?

How are beta-barrel proteins, such as porins, inserted into the outer mitochondrial membrane?

What is the estimated mass of a nuclear pore complex (NPC) in a vertebrate cell?

Proteins below what approximate molecular mass can diffuse freely through the nuclear pore complex (NPC) without active transport?

How does the monomeric GTPase Ran confer directionality on the process of nuclear import?

What is the key difference in cargo binding between nuclear import receptors and nuclear export receptors in the Ran-GTPase cycle?

During mitosis in animal cells, what is the initial event that triggers the disassembly of the nuclear lamina and the breakup of the nuclear envelope?

What is the key physical property of molecules within a biomolecular condensate that allows it to behave as a liquid and remain distinct from the surrounding cytosol?

How many nuclear pore complexes (NPCs) does a typical mammalian cell contain in its nuclear envelope?

According to the signal hypothesis, what was the initial observation that led to the discovery of signal sequences for ER import?

What happens to the synthesis of a protein when a signal-recognition particle (SRP) binds to an emerging ER signal sequence on the ribosome?

The structure of the SRP's signal sequence-binding site is a large hydrophobic pocket that allows it to bind many different signal sequences. This pocket is notably enriched in which amino acid?

How does the Sec61 translocator, a water-filled channel, prevent the leakage of small ions like calcium out of the ER when it is not actively translocating a protein?

For a single-pass transmembrane protein being inserted into the ER, what determines whether the N-terminal or C-terminal domain is translocated into the lumen?

What is the function of protein disulfide isomerase (PDI) in the ER lumen?

What lipid molecule serves as the anchor for the precursor oligosaccharide in the ER membrane before it is transferred to a protein?

In the quality control process for exporting misfolded ER proteins to the cytosol for degradation, what serves as a 'timer' that measures how long a protein has been in the ER?

What type of enzyme is responsible for transferring the preformed precursor oligosaccharide to the asparagine side chain of a protein in the ER?

In the glyoxylate cycle, which occurs in the peroxisomes of germinating seeds, what are fatty acids ultimately converted into?

What is the primary difference in the import mechanism between peroxisomes and the ER/mitochondria?

What is the typical structure of a signal sequence for import into the mitochondrial matrix?

In chloroplasts, a protein destined for the thylakoid lumen must cross three membranes. How is this accomplished?

Which statement correctly describes the topological relationship between the nuclear interior and the cytosol?

A typical Nuclear Pore Complex (NPC) is composed of a set of approximately how many different proteins, or nucleoporins?

What is the function of the phenylalanine-glycine (FG) repeats found in the unstructured domains of channel nucleoporins?

What happens to a nuclear import receptor after it releases its cargo in the nucleus?

The outer nuclear membrane is continuous with which other organelle?

When a cell synthesizes a protein with no sorting signal, where is its final destination?

What is the primary function of the smooth ER in a testosterone-secreting Leydig cell in the human testis?

What is the estimated size of the small, closed vesicles called microsomes that are formed when the ER is disrupted by homogenization?

The machinery for inserting proteins into the ER membrane is evolutionarily conserved. The components that mediate protein import into the eukaryotic ER are homologous to proteins that mediate what process in archaea?

What is the key difference between a signal sequence and a signal patch?

What would be the most likely consequence of deleting the KDEL retrieval sequence from a soluble ER resident protein like BiP?