lect 9: organelles Flashcards
what are the learning objectives of this lecture?
-know the functions of the RER
-described the structure and function of the golgi complex
-distinguish the functions of the different types of vesicle transport
what is the first step in vesicular transport?
movement from ER to golgi complex
-specialized site of transport vesicle formation on RER which is the area of no ribosomes
-transport vesicles fuse en route to golgi complex which is called the endoplasmic reticulum golgi intermediate compartment (ERGIC)
what is the structure of the golgi complex?
-stack of flattened cisternae
-regional differences in membrane composition across golgi stack
distinct functional compartments
-cis face=faces ER
-trans face=opposite side of stack
what are the functions of the golgi complex? what are the functionally distinct compartments?
“processing plant” modifies, stores, secretes molecules that it receives from the ER
Cis golgi network (CGN)
-protein sorting station back to ER ( if something accidently enters vesicle)
-next golgi station (where everything enters)
trans golgi complex (TGN)
-proteins packaged into vesicles (to go to plasma membrane or other intercellular destinations)
what is another major function of the golgi complex?
protein modification
-glycoprotein/glycolipid CHO assembly (complex polysaccharides)
-like RER, CHO sequences determined by glycosyltransferases
-RER-single core oligosaccharide
-golgi- diverse oligosaccharides
what are the models of the transport through the golgi complex?
vesicular transport model
-cargo shuttles from CGN to TGN in vesicles
cisternal maturation model
-each cistern “matures” as it moves from cis to trans face
current model (mix of both)
-like cisternal maturation but with vesicle retrograde transport
-golgi cisternae serve as primary anterograde (forward) carriers
what are types of vesicle transport?
coated vesicles
protein coats have two functions
1. causes membrane to curve and form budding vesicle
2. selects components to be carried by vesicle
what are coat proteins?
what is the graph of the formation of a coated vesicle?
what are COPII coated vesicles?
transporting cargo from ER to golgi
ER exit sites (EREs)
-specialized domains where COPII-coated vesicles bud
ER export signals
-cytosolic tails of transported proteins
proteins transported by COPII-coated vesicles
-glycosyltransferases to golgi
-vesicle docking proteins
-cargo selecting proteins
what is the structure of transport vesicles?
two layers
1. outer scaffold (outer most proteins, like clathrin, COPII)
2. inner layer
-adaptor (or adapter-like) proteins, which associated outer scaffold with vesicle itself
what are the structures of outer scaffolds of transport vesicles examples?
outer scaffold structures differ
clathrin
3-legged complexes that overlap extensively
COPII
-lattice does not overlap
-vertex formed by 4 edges
COPI
-coatamer
-7 proteins
what is the maintenance of unique membrane composition?
mechanisms
1. retention of resident molecule excluded from transport vesicles (if you dont want to leave, shouldnt put it by vesicle formation region of the ER)
2. retrieval of “escaped” molecules back to their normal enviro
-resident ER proteins have retrieval signal (amino acid sequence, C-terminal)
-protein retrieval signal recognized by specific receptors
-protein captured and transferred back to ER in COPI-coated vesicles
what are COPI-coated vesicles?
transporting escaped proteins back to the ER
lys-asp-glu-leu (arrangement found in C terminus)
-K=lysine
-D=aspatic acid
-E=glutamic acid
-L=leucine
-recognize KDEL to send back to ER via COPI
-purple=dont want
what is a recap graph?
what is the sorting of proteins at TGN of lysosomal enzymes?
-storage/transport via clathrin-coated vesicles
proteins tagged in cis-golgi
-phosphorylated mannose residues (allowa MRPS to recognize specific vesicles)
recognized/captured by mannose-6-phosphate receptors (MRPs) which recognized phosphorylated mannose
what do clathrin-coated vesicles contain?
outer lattice-clathrin
inner shell composed of GGA adaptor proteins that interact with clathrin, MPR and G-protein
G-protein=Arf1-GTP
-initiates membrane curvature
-recruits adaptors
-MRP recognizes which causes complex with ArfI (needs energy)
-induces curvature and recruits adaptors (associate with clathrin on outside)
what is the sorting of proteins at the TGN of non-lysosomal enzymes?
-not completely understood
proposed models
-released via regulated secretion (digestion enzymes, hormones): large aggregates (stored in secretory granules)
-plasma membrane proteins: constitutive secretion OR one of two TGN membrane carrier system (cell polarization determines?)
what is the two major models for intra-golgi trafficking?
what is the sorting of proteins at the TGN for targeting vesicles to a particular compartment?
- movement of vesicle toward specific target compartment
-microtubular, and motor proteins - tethering vesicles to target compartment
-mediated by diverse collection of “tethering” proteins - docking vesicles to target compartment
-close contact of membrane via interaction integral proteins - fusion
what is Rabs in targeting vesicles to a particular compartment?
-Rabs is a small G-proteins
-GTP bound
-cycles between inactive and active states
-associates with membrane via lipid anchor
-> 60 human Rab genes
-different Rabs associated with different compartments
what are snares?
SNAREs
-family of integral proteins
-localized to specific subcellular compartments
-bring vesicle and target compartment in close contact
-v-SNAREs
-t-SNAREs
what is the example of targeting vesicles to a particular compartment in neurons?
what is exocytosis?
