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TOPIC 4
ENDO SYSTEM
| Term | Definition |
|---|---|
| what is the endomembrane system | • comprised of ER, Golgi, endosomes and lysosomes • does NOT included perosixomes |
| what is the endoplasmic reticulum | • proteins destined for plasma membrane, organelles and export • biosynthesis of lipids |
| explain RER | • ribosomes embedded in the ER give the rough appearance • site of protein production and modification and lipid synthesis |
| how can proteins be made by bound and free ribosomes | explain both free ribosomes... and bound ribosomes... |
| what is the single mechanism (steps 1&2) | 1. SRP recognizes & binds both signal sequence and large ribosomal subunit; translation stops momentarily 2. docking ribosome to ER membrane occurs by 2 key interactions... 1 between the SRP and SRP receptor and other between ribosome & translocon |
| single mechanism (3&4) | 3. SRP and SRP receptor each bind a molecule of GTP... triggers the restart of translation, opening of the pore, and the insertion of the signal sequence into the pore 4. GTP hydrolysis results in release of the SR |
| single mechanism (5&6) | 5. during translation, signal sequence typically removed by signal peptidase & degraded 6. the result is, protein that now a soluble protein within ER lumen; further processing occurs ( glycosylation &various modifications may occur in ER or Golgi) |
| protein w internal stop transfer sequence and terminal er seq. | steps a and b |
| what is N-glycosylation | most proteins made at RER =N-glycosylated in cotranslational manner by oligosaccharyltransferase( transmembrane protein complex of RER) • all proteins receiving N-linked oligosaccharide given same “core oligosaccharide” • oligo added by oligotransferas |
| what is drug detoxification | RH + NAD(P)H + H+ + O2 ROH + NAD(P)+ + H2O • often takes place in liver cells • hydroxylation often the first step • increases solubility and introduces a site for further modification (often conjugation) |
| what is oxidation and excretion | oxidation and conjugation Oxidation p450 in the liver, plays a major role molecule |
| what is conjugation | describe both positive and negative outcomes |
| what is carbohydrate metabolism | - glucose-6-phosphatase localizes to SER -involved in releasing glucose from glycogen storage molecule - allows glucose to leave liver |
| Calcium Storage: | - pumped into SER by ATP-dependent calcium ATPases -important for signalling (we will return to this |
| Steroid Biosynthesis: | - biosynthesis of cholesterol and steroid hormones Figure 12-2 |
| ER & lipid biosynthesis | • most lipid biosyn. enzymes exclusive to ER • means most phospholipids & cholesterol manufactured on cytosolic face of ER • require flippases (+distribution &asymmetry) • moved by endo & cytosolic exchange proteins (phospholipid transfer proteins) |
| explain Golgi | • cis face oriented towards ER, trans face away from the ER • compartments are biochemically and functionally distinct • two models of formation: 1. stationary cisternae model 2. cisternal maturation model |
| difference between anterograde and retrograde transport | • anterograde movement is movement from the ER through the Golgi towards the plasma membrane • how does this affect the overall membrane balance? • retrograde transport is the flow of vesicles from the Golgi back toward the ER |
| role for Golgi in glycosylation | • N-linked glycosylation initiated in the ER • role in protein folding • as proteins move through the Golgi, N-glycosyl group is modified • contain many glucan synthetases and glycosyl transferases |
| what are some challenges in protein trafficking + diagram | • proteins localize to ER, Golgi, endosomes, lysosomes, plasma membrane and extracellular space • proteins utilize a variety of tags for sorting • membrane lipids may also be tagged to direct trafficking of vesicles |
| explain retaining/retrieving ER proteins | • resident ER proteins are either retained or retrieved • kin recognition may allow proteins to be retained • retention tags may also keep proteins in the ER • in contrast, retrieval tags such as KDEL and KKXX may be used to return ER proteins |
| what are Golgi complex proteins | resident Golgi proteins are integral membrane proteins with one or more transmembrane regions • does membrane thickness determine which subcellular compartment of the Golgi they occupy? • membrane increases in thickness from about 5nm to 8nm |
| How does sorting lysosomal proteins work | • mannose-6-phosphate tag on lysosomal proteins • binding to mannose-6- phosphate receptor (MPR) at pH 6.4 (Golgi) • release at pH 5.5 (endosomes) |
| describe I-cell disease | • MLII on this chart is I-cell disease • lysosomal storage disease |
| what are the secretory pathways and the 4 steps | Secretory Pathways • movement of proteins from the Gogli complex to the exterior of the cell • in this slide, RER=rough endoplasmic reticulum, CV=condensing vacuole, ZG=zymogen granule, L=lumen (which in this case is the extracellular space) |
| what is constitutive secretion | unregulated and continuous secretion • thought to be default pathway (no tag, no retention in endomembrane system) • may not b simple, as short amino acids tags may be implicated in constitutive secretion • glycosylation may play a role in secretion |
| what is regulated secretion | • secretory vesicles accumulate in the cell, but only fuse with the plasma membrane in response to a specific signal • vesicles bud from TGN and undergo maturation • maturation involves concentrating the proteins, and sometimes also modifying the |
| difference between constitutive and secretory | CONSTITUTIVE: default pathway unless signalled to do otherwise SECRETORY: signals upon receiving a signal another look at secretion Figure 13-65a Molecular Biology of the Cell (© Garland Science 2008) |
| mast cells | A & B |
| difference between exocytosis and endocytosis | exocytosis and endocytosis Fig. 12-8 exocytosis transporting materials across the PM, OUT of the cell endocytosis transporting materials across the PM, INTO of the cell |
| polarized secretion/ calcium | • calcium: elevated intracellular calcium often associated w exocytosis • calcium =second messenger • polarized secretion: exocytosis limited to specific region plasma membrane • requires localized recognition sites on subdomains of plasma membrane |
| how do vesicles move | • not fully understood • evidence that vesicles move along microtubule tracks • vesicular trafficking stopped in presence of colchicine (which is a microtubule assembly inhibitor) |
| what're microtubules and the cytoskeleton | • cytoskeleton is a network of proteins within a eukaryotic cell • polymeric proteins • in this slide, nucleus is blue, actin filaments are red and microtubules are green |
| vesicle attached to microtubule | • this image uses transmission electron microscopy to visualize a vesicle associated with a microtubule |
| what are motor proteins | • utilize ATP hydrolysis to move along microtubules • dyneins move towards minus end • kinesins move towards plus end |
| endocytosis in detail | • may be important for bringing materials into a cell (membrane transport) or play a role in defense (phagocytosis) • exocytosis and endocytosis must balance out. Why? • where do the vesicles end up? |
| phagocytosis | • ingestion of large particles (can be more than 0.5 μm in diameter) • in animals, mainly carried out by neutrophils, macrophages (components of the immune system) |
| receptor-mediated endocytosis | • also called clathrin- dependent endocytosis • requires receptors on the outer surface of the PM • general mechanism shown on this slide |
| RMEndo | • can take up specific molecules • > than 25 different receptors identified • single clathrin-coated pit holds abt 1000 receptors • despite fact that ultimate cell fate of all endocytosed molecules may be different, all enter same endosomal compart. |
| LDL receptor-mediated endocytosis | • LDL = low density lipoprotein • chol.largely manufactured liver, transported in lipoproteins which holds 1500 cholesteryl molecules (immature) also 800 phospholipids and one protein • released when pH drops, hydrolyzed to cholesterol in lysosomes |
| receptor-mediated encodytosis | • not all ligands dissociate in early endosomes • receptor-ligand complexes may b sorted --> different transport vesicles • altern fates include 1) carried lysosome 4 degradation 2) carried 2 TGN, sorted by Golgi w variety of desti. 3) transcytosis |
| receptor-independent encodytosis | • pinocytosis or “cell sipping” non-specific • vesicles generally about 100nm in diameter • generally start with clathrin-coated pits or caveolae • caveosomes form from lipid rafts |
| receptor-independent encodytosis | • proteins enter cell by caveosomes avoid endosomes & lysosomes • ex. of pinocytosis rates: macrophages ingest 3% of their plasma membrane / min; fibroblasts 1% / min • cell volume & SA remain constant, ∴endocytic and exocytic pathways are equivalent |
| what are coat proteins | diagram |
| clathrin | • first coat protein identified • triskelion – 3 large and 3 small polypeptides clathrin polymerizes into a “soccer ball” shape |
| Clathrin coat assembly simplified | Coat assembly is Initiated by ARFs (GTPase) Adaptin binds to target receptor And begins coat assembly Clathrin assembly is tightly Associated Dynamin (GTPase) mediates Membrane pinching off Coat disassembly – Hsp70 family protein (ATPase) |
| dynamin | DYNAMIN – PI(4,5)P2 binding domain and GTPase domain •GTP hydrolysis is required for pinching off Dynamin |
| What are G proteins a form of molecular switch | GAPs = GTPase-accelerating protein RGSs = regulators of G protein signaling GDIs = guanine nucleotide dissociation inhibitors GEFs = guanine nucleotide-exchange factors |
| COPI and COPII coat formation | • for COPI and clathrin at Golgi: initiated by ARF protein • for COPII: utilizes Sar1 for initiation • release may be caused by self-hydrolysis of GTP to GDP |
| how do snares mediate membrane fusion | diagram 4 steps |
| explain crystal structure of a SNARE complex | • this SNARE complex in neurons results in neurotransmitter vesicle fusion and release of neurotransmitter into the synaptic cleft |
Created by:
mackenzieecarroll
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