Chapter 15: Intracellular Components and Protein Transport

Vocabulary practice flashcards covering eukaryotic organelles, protein sorting mechanisms, vesicular transport, and endocytic/secretory pathways based on Chapter 15.

Membrane-Enclosed Organelles

Organelles in a eukaryotic cell that are surrounded by a lipid bilayer, contain a unique set of molecules, and carry out specialized functions or metabolic processes.

Cytosol

The intracellular compartment enclosed by the plasma membrane that contains metabolic pathways, protein synthesis machinery, and the cytoskeleton.

Nucleus

Organelle that contains the main genome, serves as the site for DNA and RNA synthesis, and communicates with the cytosol via nuclear pores in the nuclear envelope.

Endoplasmic Reticulum (ER)

A system of interconnected membranous sacs and tubes that serves as the major site of synthesis of new membranes, most lipids, and proteins destined for organelles or the plasma membrane.

Rough ER

Region of the endoplasmic reticulum with ribosomes attached to its cytosolic surface that synthesize proteins into the ER lumen.

Smooth ER

Region of the endoplasmic reticulum lacking ribosomes; functions in steroid hormone synthesis in endocrine cells of the adrenal gland, alcohol detoxification in the liver, and calcium sequestration for muscle contraction.

Golgi Apparatus

An organelle typically located near the nucleus that receives proteins and lipids from the ER to modify, sort, and package them for secretion or delivery to other organelles.

Lysosomes

Small membranous sacs containing digestive hydrolytic enzymes that degrade worn-out or damaged organelles and macromolecules taken into the cell.

Endosomes

Membrane-enclosed compartments that sort ingested endocytosed material and recycle selected molecules back to the plasma membrane.

Peroxisomes

Small membrane-enclosed organelles containing enzymes that break down lipids, carry out the oxidative breakdown of toxic molecules, and produce hydrogen peroxide.

Endomembrane System

An interconnected network of membrane-enclosed organelles in a eukaryotic cell, comprising the ER, Golgi apparatus, lysosomes, peroxisomes, and endosomes.

Sorting Signal

An amino acid sequence that directs a protein to a specific organelle; proteins that lack a sorting signal remain in the cytosol.

Protein Translocators

Membrane-bound protein complexes that transport unfolded proteins across the membranes of organelles such as mitochondria and chloroplasts.

Nuclear Lamina

A meshwork of protein filaments lining the inner nuclear membrane that provides structural support and acts as an anchorage site for chromosomes.

Nuclear Pores

Selective gate channels perforating the nuclear envelope that permit free diffusion of small molecules and actively transport specific macromolecules.

Nuclear Localization Signal

A sorting signal sequence on proteins recognized by cytosolic nuclear import receptors that allows macromolecules to pass through nuclear pores.

Ran

A GTPase that guides nuclear transport via GTP hydrolysis; exists predominantly as Ran-GTP in the nucleus and Ran-GDP in the cytosol.

Zellweger Syndrome

A severe disease caused by mutations affecting peroxisomal protein import, resulting in brain, liver, and kidney issues, with affected individuals surviving only around $6\,\text{months}$.

ER Signal Sequence

A peptide sequence of $8+$ hydrophobic amino acids that directs a nascent protein and its translating ribosome to the endoplasmic reticulum.

Signal-Recognition Particle (SRP)

A cytosolic complex that binds to both the ribosome and the emerging ER signal sequence, guiding them to the SRP receptor on the ER membrane.

Stop-Transfer Sequence

An amino acid sequence that halts translocation across the ER membrane, anchoring the protein within the lipid bilayer as a transmembrane protein.

Coated Vesicles

Small membrane-enclosed transport sacs that have a distinctive layer of proteins on their cytosolic surface, which shapes the membrane into a bud and captures cargo before shedding.

Clathrin

A coat protein that forms the outer cage of transport vesicles budding from the Golgi apparatus or the plasma membrane.

Dynamin

A GTP-binding protein that forms a constricting ring around the neck of deeply coated pits to pinch off the vesicle.

Adaptins

Proteins that secure the clathrin coat to the vesicle membrane and capture specific cargo receptors displaying transport signals.

Rab Proteins

A family of small GTP-binding proteins on vesicle and organelle surfaces that serve as molecular markers to ensure vesicles dock with the correct target membrane.

Tethering Protein

A filamentous transmembrane protein on a target membrane that binds Rab proteins to dock incoming transport vesicles.

SNAREs

A family of membrane proteins responsible for catalyzing the selective fusion of transport vesicles with their target membrane inside the cell.

Exocytosis

The pathway by which molecules packaged in membrane-enclosed vesicles fuse with the plasma membrane to secrete their contents to the cell exterior.

Unfolded Protein Response (UPR)

A cellular program triggered by an accumulation of misfolded proteins in the ER that induces the expansion of the ER and increases the production of protein-folding machinery.

Cisternae

The flattened, membrane-enclosed sacs of the Golgi apparatus through which proteins migrate and mature from the cis to the trans face.

Constitutive Exocytosis Pathway

A continuous pathway that supplies the plasma membrane with newly synthesized lipids and proteins, operating in all eukaryotic cells without a specific regulatory trigger.

Endocytosis

The process by which cells ingest extracellular materials via invaginations of the plasma membrane that pinch off into intracellular membrane-enclosed vesicles.

Pinocytosis

A form of endocytosis that involves the ingestion of fluid and small molecules via small pinocytic vesicles; also known as cellular drinking.

Phagocytosis

A specialized endocytic process involving the engulfment of large particles, such as microorganisms or cellular debris, into large vesicles called phagosomes.

Pseudopods

Sheetlike extensions of the plasma membrane produced by phagocytic cells via cytoskeletal rearrangement to engulf large target particles or bacteria.

Receptor-Mediated Endocytosis

A selective uptake mechanism in which specific macromolecules bind cell surface receptors and are internalized in clathrin-coated vesicles.

Transcytosis

The transport of endocytosed material and receptors across a cell to a completely different domain of the plasma membrane.

Autophagy

A catabolic pathway by which a cell degrades its own obsolete or damaged organelles and molecules by enclosing them in autophagosomes for fusion with lysosomes.