All flashcards
Flashcard 1: What pH change in early endosomes promotes ligand–receptor dissociation?
Answer: Acidification due to V-type H+-ATPase activity. Proton pumping by V-ATPase lowers endosomal pH, inducing conformational changes that separate ligands from receptors for proper sorting.
Flashcard 2: What is the early endosome’s main role in endocytosis?
Answer: Primary sorting station for internalized cargo and receptors. Early endosomes receive and sort endocytosed materials, directing receptors for recycling and ligands for degradation based on pH-dependent dissociation.
Flashcard 3: What is the function of adaptin (AP) complexes in clathrin-mediated endocytosis?
Answer: Link cargo receptors to clathrin by binding sorting motifs in cytosolic tails. Adaptins recognize specific motifs on receptor tails, bridging them to clathrin to ensure selective cargo incorporation into forming vesicles.
Flashcard 4: What is the naming distinction between v-SNAREs and t-SNAREs?
Answer: v-SNAREs are on vesicles; t-SNAREs are on target membranes. This classification distinguishes vesicle-associated SNAREs (v) from target membrane SNAREs (t), ensuring directional and specific fusion.
Flashcard 5: Which GTPase mediates scission of clathrin-coated vesicles from the plasma membrane?
Answer: Dynamin. Dynamin assembles into a collar at the vesicle neck, and its GTP hydrolysis constricts and severs the membrane to release the vesicle.
Flashcard 6: Which coat protein is classically associated with receptor-mediated endocytosis at the plasma membrane?
Answer: Clathrin. Clathrin forms a polyhedral lattice around pits, driving membrane curvature and vesicle formation for selective cargo uptake.
Flashcard 7: What is receptor-mediated endocytosis?
Answer: Selective uptake of ligands via receptors concentrated in coated pits. It facilitates efficient, specific internalization of essential molecules by clustering ligand-bound receptors in pits that form coated vesicles.
Flashcard 8: Which motor protein generally moves vesicles toward the microtubule minus end (centrosome)?
Answer: Dynein. Dyneins harness ATP to move cargo along microtubules toward minus ends, supporting retrograde transport to central cellular regions.
Flashcard 9: What is constitutive exocytosis?
Answer: Continuous, unregulated secretion and membrane delivery to the cell surface. It maintains steady-state secretion of proteins and lipids, supporting cell growth and membrane turnover without external stimuli.
Flashcard 10: What is regulated exocytosis?
Answer: Signal-triggered vesicle fusion, often Ca2+-dependent (e.g., neurotransmitters). It allows rapid, controlled release of stored contents in response to signals, crucial for processes like synaptic transmission.
Flashcard 11: What is the fate of most receptors after ligand release in early endosomes?
Answer: Recycling back to the plasma membrane. Receptor recycling conserves cellular resources by returning unbound receptors to the surface for further ligand binding and uptake.
Flashcard 12: What is a lysosome?
Answer: Acidic organelle containing hydrolytic enzymes for macromolecule degradation. Lysosomes maintain an acidic environment optimal for enzyme activity, breaking down internalized materials into reusable components.
Flashcard 13: What is phagocytosis?
Answer: Engulfment of large particles into phagosomes, typically by immune cells. This mechanism enables specialized cells to ingest large particles like pathogens by extending pseudopods and forming phagosomes for degradation.
Flashcard 14: What is pinocytosis?
Answer: Nonselective endocytosis of extracellular fluid and dissolved solutes. It allows cells to non-specifically sample and uptake surrounding fluid and solutes through small vesicle formation for nutrient acquisition.
Flashcard 15: What is exocytosis?
Answer: Secretion by vesicle fusion with the plasma membrane. This mechanism releases cellular contents extracellularly or incorporates membrane proteins by merging vesicle membranes with the plasma membrane.
Flashcard 16: What is endocytosis?
Answer: Uptake of extracellular material via membrane invagination and vesicles. This process enables cells to internalize molecules and particles that cannot diffuse across the plasma membrane by forming intracellular vesicles.
Flashcard 17: What is the typical fate of cargo destined for degradation after endocytosis?
Answer: Trafficking to late endosomes and then lysosomes. Cargo marked for breakdown progresses through endosomal maturation to lysosomes, ensuring degradation and nutrient recycling.
Flashcard 18: What post-translational tag commonly targets membrane proteins for lysosomal degradation?
Answer: Ubiquitination. Ubiquitin tags signal sorting into multivesicular bodies via ESCRT complexes, directing proteins to lysosomes for proteolysis.
Flashcard 19: Which coat protein is associated with ER-to-Golgi anterograde transport?
Answer: COPII. COPII coats assemble on ER membranes to form vesicles that transport newly synthesized proteins forward to the Golgi apparatus.
Flashcard 20: Which coat protein is associated with Golgi-to-ER retrograde transport?
Answer: COPI. COPI coats facilitate vesicle formation for retrieving escaped ER proteins and recycling components back from the Golgi.
Flashcard 21: What is the function of SNARE proteins in vesicular trafficking?
Answer: Mediate specific vesicle docking and membrane fusion. SNAREs form trans-complexes that zipper membranes together, providing energy and specificity for fusion events in trafficking pathways.
Flashcard 22: What is the role of Rab GTPases in vesicular trafficking?
Answer: Provide targeting specificity by recruiting tethering and docking factors. Rabs cycle between GTP- and GDP-bound states to recruit effectors that guide vesicles to correct destinations and promote docking.
Flashcard 23: Which cytoskeletal track is most associated with long-range vesicle transport in cells?
Answer: Microtubules. Microtubules provide polarized tracks for efficient, directed transport of vesicles over long distances within the cell.
Flashcard 24: Which motor protein generally moves vesicles toward the microtubule plus end (cell periphery)?
Answer: Kinesin. Kinesins use ATP hydrolysis to walk along microtubules toward plus ends, facilitating anterograde transport to peripheral sites.