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What are coated vesicles?
These are vesicles that bud from a membrane compartment that typically has a multi-subunit protein coat which promotes the budding process and binds specific membrane proteins
What are the 3 best known coated vesicles?
COP1 function
Move materials in a ^^retrograde^^ direction fromthe ERGICandGolgistack backward towardtheER and from ==trans Golgi cisternae== “backward” ==to cis Golgi cisternae==
COP 2 function
Clathrin-coated vesicles
Move materials from the Golgi to the TGN to endosomes, lysosomes, and plant vacuoles. They also move materials from the plasma membrane to cytoplasmic compartments along the endocytic pathway and have also been implicated in trafficking from endosomes and lysosomes.
What types of proteins are transported with COP2 vesicles? How does the COP2 proteins (Sec 13, 23, 24, 31), Sar, GTP, GEF and cargo receptors interact during the formation of COP2 vesicles?
How are COP2 vesicles assembled and disassembled?
Find answer in book
G-Proteins
Discuss, in detail, how COPI vesicles are able to help maintain the appropriate distribution of proteins in the Golgi and RER: retention
Retention: resident molecules that are excluded from transport vesicles are based mostly on the physical properties of the protein
Discuss, in detail, how COPI vesicles are able to help maintain the appropriate distribution of proteins in the Golgi and RER: retrieval
Retrieval: Escaped molecules back to the compartment in which they typically reside
Exactly how are these vesicles able to recognize the proteins they are supposed to transport?
How are lysosomal enzymes targeted to the lysosome?
Lysosome formation
Look at picture:
Describe in detail the 4 steps involved in the targeting of a vesicle to a particular membrane compartment and include important molecular components
Moving
Moving is mediated by microtubules (microtubule transport) and motor proteins (motor protein transport)
Tethering
Is mediated by a collection of tethering proteins which can form a molecule bridge between 2 membranes. G-protein (Rab-GTP) is an on/off switch. There is a loose connection with the tether and target.
Docking
Has key proteins that make this possible (v-snares are for vesicles, t-snares are used for target proteins)
Fusing
The target and membrane compartment merge and form a connection. As the vesicle and site below fuses, there’s an opening between them; therefore, what was in the vesicle can get into the protein now.
How is the specificity of the process maintained?
Maintained through ^^exocytosis^^ where secretory vesicles go to the top of the membrane, and then are excreted
v-SNARE (synaptobrevin)
Involved in docking and fusion
Lysosome contents: Pick 2 enzymes and learn those
Discuss the contents of a lysosome
Define autophagy
Autophagy process
Phagocytosis
Carried out by a few types of cells specialized for the uptake of relatively large particles from the environment.
Phagocytic pathway
Defects in lysosomes
Tay-Sachs disease
What are the 2 basic mechanisms of endocytosis?
Bulk-phase endocytosis (pinocytosis)
Receptor-mediated endocytosis (RME aka clathrin-mediated endocytosis)
Definition: Brings about the uptake of specific extracellular macromolecules (ligands) following their binding to receptors on the external surface of the plasma membrane
Similarities between bulk-phase endocytosis and receptor-mediated endocytosis
COP2 vs clathrin similarities
Structure of clathrin-coated vesicles in RME
Clathrin-triskelion and AP2 adaptor roles
Clathrin vesicles: role of dynamin
Function of dynamin and GTP
Summary of steps: Dynamin subunits, clathrin lattice, dynamin ring, GTP hydrolysis or GTPyS
Function of dynamin and GTP: step 0
The clathrin lattice of the coated pit
Function of dynamin and GTP: step 1
Undergoes rearrangement to make an invaginated vesicle connected to the overlying plasma membrane by a stalk
Function of dynamin and GTP: step 2
Th dynamin subunits concentration the region undergoes polymerization to make a ring around the stalk
Function of dynamin and GTP: step 3
Changes in the conformation of the ring, which are thought to be induced by GTP hydrolysis
Function of dynamin and GTP: step 4
Lead to fission of the coated vesicle from the plasma membrane and disassembly of the dynamin ring
Function of dynamin and GTP: step 5
If vesicle budding occurs in the presence of GTPyS, a nonhydrolyzable analog of GTP, dynamin polymerization continues beyond the formation of a simple collar, producing a narrow tubule constructed from several turns of the dynamin helix
Discuss, in general, the endocytic pathway paying attention to the roles played by early endosomes, late endosomes, and the sorting compartment (figure 8.45).
Receptors taken up by endocytosis are transported in vesicles to early endosomes which serve as a sorting station that direction different types of receptors and ligands along different paths
Pathway:
The movement of materials from the extracellular space to early endosomes where sorting occurs
Endocytosis of two types of receptor-ligand complexes:
Signaling receptors like the EGF receptor is typically transported to late endosomes along with their ligands.
Housekeeping receptors
Receptors taken up by endocytosis are transported to an early endome which serves as a sorting station that directs the different types of receptors and ligands along different pathways. Housekeeping receptors typically disassociate from their bound ligands as a result of the high H+ concentration of the early endosomes. The receptors are then concentrated into specialized tubular compartments of the early endosome which represent recycling centers. Vesicles that bud from these tubules curry receptors back o the plasma membrane for additional rounds of endocytosis.
Signal receptors
In contrast, released ligands become concentrated into a sorting compartment before being dispatched to a late endosome and ultimately to a lysosome, where final processing occurs.
Housekeeping vs signaling receptors
Taking in things into the cell that the cell wants to take in, the red ones go back to the surface again, the early endosome sorts the housekeeping ones so that they stay in the surface?; the stuff in the sorting station that didn’t get sent out go to the sorting endosomes
Compare in general terms the way proteins are transported into the RER with how they are transported into the nucleus, peroxisomes, mitochondria, and chloroplasts. Explain, in detail, how proteins enter the mitochondria. Be sure to delineate between membrane and matrix proteins.
Nucleus
Peroxisomes
Mitochondria and chloroplasts
Both import proteins that must assume an unfolded state.
Chloroplasts
How proteins enter the mitochondria
Peroxisomes
Able to import peroxisomal matrix proteins in their native, folded conformation.
Mitochondria and chloroplasts
Both import proteins that must assume an unfolded state.
Chloroplasts
How proteins enter the mitochondria