Cell Biology Chapter 15

What enables cells to create barriers that confine molecules to specific compartments?

Membrane-enclosed organelles.

Name examples of membrane-enclosed organelles in eukaryotic cells.

Nucleus, ER, Golgi apparatus, lysosomes, endosomes, peroxisomes, mitochondria, chloroplasts (in plants)

What is the endomembrane system?

A group of organelles including the ER, Golgi apparatus, lysosomes, endosomes, and peroxisomes.

Where are most organelle proteins made?

In the cytosol.

How are proteins sorted to specific organelles?

By sorting signals in their amino acid sequences.

How are nuclear proteins transported into the nucleus?

Through nuclear pores using nuclear localization signals.

Do proteins enter mitochondria and chloroplasts folded or unfolded?

Unfolded during transport.

What does the ER synthesize?

Most cellular lipids and many proteins.

What targets ribosomes to the ER?

Signal-recognition particles (SRPs).

How do water-soluble and transmembrane proteins differ in ER transport?

Water-soluble proteins enter the ER lumen fully; transmembrane proteins remain anchored in the membrane.

What happens to proteins inside the ER lumen?

They fold, assemble, form disulfide bonds, and receive oligosaccharides.

What is the role of chaperone proteins in the ER?

They help misfolded proteins refold and prevent aggregation.

What happens if misfolded proteins accumulate in the ER?

The unfolded protein response is triggered.

How are proteins transported between organelles?

By vesicular transport.

What helps shape budding vesicles?

Coat proteins like clathrin.

What must vesicles shed before fusing with a target membrane?

Their protein coat.

What proteins mediate vesicle docking and fusion?

Rab proteins, tethering proteins, and SNAREs.

What happens in the Golgi apparatus?

Proteins are modified, sorted, and dispatched to destinations.

What is constitutive exocytosis?

Continuous delivery of proteins and lipids to the plasma membrane.

What is regulated exocytosis?

Controlled release of stored molecules upon receiving a signal.

What is endocytosis?

Uptake of fluid, molecules, or particles by vesicle formation from the plasma membrane.

What happens to endocytosed material?

Delivered to endosomes, then lysosomes for degradation, while membrane components are recycled.

Autophagy

Process where a cell digests its own organelles or proteins to recycle components.

Clathrin

Protein that forms a coated lattice around budding vesicles.

Coated vesicle

Vesicle covered with proteins that help shape it and select cargo.

Endocytosis

Uptake of external substances by vesicle formation from the plasma membrane.

Endomembrane system

A connected system of organelles involved in synthesis, transport, and degradation.

Endoplasmic reticulum (ER)

The organelle where lipid and protein synthesis occurs.

Endosome

Membrane compartment that sorts endocytosed materials.

Exocytosis

Process of vesicles fusing with the plasma membrane to release contents outside the cell.

Golgi apparatus

Organelle that modifies, sorts, and packages proteins and lipids.

Lysosome

Organelle containing digestive enzymes to degrade materials.

Membrane-enclosed organelle

An organelle bounded by a lipid bilayer.

Nuclear envelope

Double membrane enclosing the nucleus.

Nuclear pore

Large complex allowing passage of molecules between nucleus and cytosol.

Peroxisome

Organelle involved in oxidative reactions and lipid metabolism.

Phagocytic cell

A cell that engulfs and digests large particles or cells.

Phagocytosis

Ingestion of large particles by cells.

Pinocytosis

Ingestion of fluid and small molecules by cells.

Rab protein

Small GTP-binding proteins that regulate vesicle targeting.

Receptor-mediated endocytosis

Selective uptake of molecules bound to cell-surface receptors.

Rough endoplasmic reticulum

ER studded with ribosomes for protein synthesis.

Secretion

Release of cellular products to the cell exterior.

Secretory vesicle

Vesicle storing substances to be released via regulated exocytosis.

Signal sequence

Short amino acid sequence directing proteins to a specific organelle.

SNARE

Proteins facilitating vesicle docking and membrane fusion.

Tethering protein

Protein that helps attach a vesicle to its target membrane before fusion.

Transport vesicle

Small vesicles move molecules between organelles or to the plasma membrane.

Unfolded protein response

Cellular response to an accumulation of misfolded proteins in the ER.

Vesicular transport

Movement of materials in vesicles between organelles or to/from the cell surface.