Ch13b Key terms

  1. When vesicles are made in the ER, proteins, membrane proteins, cargo, and lipids are transported out. Proteins that should stay in the ER lumen sometimes escape due to getting stuck in the transport process.

  2. Vesicular tubular clusters form when vesicles leaving the ER fuse together due to interactions between v-SNAREs and t-SNAREs. They appear blobby under a microscope because they are amorphous and irregular in shape, not perfectly round like individual vesicles.

  3. Vesicles target the ER via SNARE proteins (v-SNAREs on the vesicle, t-SNAREs on the target membrane). Rabs deliver SNAREs to the appropriate location so that they can unwind and fuse.

  4. The KDEL sequence is a signal sequence on soluble ER proteins that ensures their retention within the ER lumen. It binds to the KDEL receptor, which facilitates their return from the Golgi back to the ER.

  5. Some ER proteins must be soluble to function properly, as their function or conformation may be inhibited if they were bound to a membrane. Additionally, there is a limited amount of membrane space.

  6. The KDEL receptor does not bind to KDEL proteins within the ER lumen because the ER lumen's environment does not allow for the necessary conformational change in the receptor. The receptor only binds in the more acidic environment of the Golgi.

  7. In the vesicular transport model, proteins are transported between Golgi cisternae by vesicles. In the cisternal maturation model, the Golgi cisternae themselves mature and change, moving proteins along with them.

  8. Acid hydrolases are enzymes within lysosomes that break down various macromolecules, including proteins, nucleic acids, lipids, and carbohydrates. Their activity is pH-dependent because they are only active in the acidic environment (pH 5) of the lysosome, protecting the rest of the cell from unwanted degradation.

  9. Autophagy is a process by which damaged or unnecessary cellular components, like mitochondria, are degraded. A double membrane is created around the organelle to isolate it and ensure that all of the inner components, membrane proteins, etc. will also be degraded.

  10. To bring cargo into the cell, the cargo binds to its appropriate receptor. This causes a conformational change, which allows adapter proteins to bind, followed by coat proteins. Once the vesicle pinches off, it is then able to fuse with an endosome.

  • Adapter Proteins: Proteins that link cargo receptors to coat proteins during vesicle formation.

  • Autophagy: A cellular process in which damaged or unnecessary cellular components are degraded.

  • Cis Golgi: The Golgi compartment closest to the ER, where proteins enter the Golgi apparatus.

  • Cisternal Maturation Model: A model of Golgi function in which the Golgi cisternae themselves mature and move through the Golgi stack, carrying proteins with them.

  • Clathrin: A coat protein that assembles into a lattice-like structure, driving membrane curvature and vesicle formation.

  • Coat Proteins: Proteins that bind to the membrane and drive vesicle formation.

  • Endocytosis: The process by which cells internalize molecules or particles from the extracellular environment by engulfing them in vesicles.

  • ER (Endoplasmic Reticulum): An organelle involved in protein and lipid synthesis.

  • ER Lumen: The space between the ER membranes.

  • Exocytosis: The process by which cells release molecules or particles to the extracellular environment by fusing vesicles with the plasma membrane.

  • Golgi Apparatus: An organelle involved in modifying, sorting, and packaging proteins and lipids.

  • KDEL Receptor: A receptor protein that binds to the KDEL sequence, facilitating the retrieval of ER-resident proteins from the Golgi.

  • KDEL Sequence: A signal sequence (Lys-Asp-Glu-Leu) found on soluble ER proteins that promotes their return from the Golgi to the ER.

  • Lysosome: An organelle containing acid hydrolases that degrade cellular waste and debris.

  • Mannose-6-Phosphate (M6P): A sugar modification added to lysosomal enzymes in the Golgi, targeting them for delivery to lysosomes.

  • Phagocytosis: A type of endocytosis in which cells engulf large particles, such as bacteria or cellular debris.

  • Pino Endocytosis: A type of endocytosis that brings small molecules into a cell.

  • Proteases: Enzymes that cleave proteins.

  • Signal Sequence: A short amino acid sequence that directs a protein to a specific location within the cell.

  • SNAREs (Soluble NSF Attachment Receptor Proteins): Proteins that mediate the fusion of transport vesicles with their target membranes.

  • Trans Golgi: The Golgi compartment farthest from the ER, where proteins exit the Golgi apparatus.

  • Vesicle: A small, membrane-bound sac used to transport substances within the cell.

  • Vesicular Tubular Cluster: A cluster of vesicles that transport proteins from the ER to the Golgi.

  • Vesicular Transport Model: A model of Golgi function in which proteins are transported between Golgi cisternae by vesicles.

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