Cell Biology 18- Organelle 2nd Sung Youn Lee, PhD. StudentVeterinary collage, Room 32002 450 3719, 016 293 6059leevet@paran.com

Membrane lipidsThe synthesis of membrane phospholipids, cholesterol, and ceramide occurs within the ER, usually SER.The synthesis of phospholipids occurs on the cytoplasmic leaflet of ER membrane.Flippases ; newly synthesized phospholipids can be moved to the luminal leaflet of the ER.ER--> target organelleBud-fusion ; Golgi, lysosome, plasma membraneProtein (water soluble exchage protein) ; mitochondria and peroxisome

phosphatydylcholine

flippase

Golgi apparatusFunction ; posttranslational modification and sorting of protein and lipids synthesized within ER.Glycosylation (O-linked)InsulinCGN, cis-, medial-, trans-, TGNDistribution of cis-Glogi network; KEDL(ER retention signal) ; return it to ERDistribution of trans-Glogi network; Sort into different transport vescles destined for the lysosomes, plasma membranes, or secretion

Targeting of acid hydrolases to the lysosomeThe lysosomes contain acid hydroase protease, nuclease, glycosidase, lipase, phospholipase, sulfase, and phosphataseAcid hydrolases are active at pH 5.0, but inactive at neutral pH of the cytoplasm.Acidic pH of the inner lysosome is maintained by an ATP-dependent proton pump in the lysosomal membrane. V-class ATPase

V-typeATPase

= lysosome ?

Types of ATPaseP-classNa+ K+ ; Na+3(out), K+2(in), animal tissueCa2+ ; maintain low Ca2+ in cytosol, myocyte (sarcoplasmic reticulum)V-classH+ ; lysosome(endosome) & vacule highly acidic (pH 5.0-5.5)ABC (ATP binding cassette)MDR ATPase ; multidrug resistance ATPaseCystic fibrosis transmembrane regulator

Material for destructionPhagocytosis macrophage and neutrophilReceptor mediated endocytosis clathrin-coated pitAutophagy first wrapped with ER derived membrane and then fused with lysosomeKFERQ selectively taken by lysosomes

Proteolytic pathwayIn addition to lysosomal destruction. The cytoplasm has several proteolytic enzymes.Proteins have Met, Ser, Thr, Ala, Val. Cys, Pro, or Gly as their NH2-terminal amino acids are stabilized against proteolysis.Others modified by binding of ubiquitin, linked to lysine at the NH2-termini --> to identify the substrate of ATP-dependent protease

Protein and lipid destined for plasma membraneGolgi retention signal ; membrane spanning -helical segment of transmembrane proteins.Constitutive secretion or exocytosisno signal ; default pathwayRegulatory exocytosisRequire a chemical signal (Ca2+)Targeting for plasma membraneGPI ; TGN --> plasma membraneCytoplasm --> plasma membrane --> sort by endocytosis

InternalizeExocytosis adds new membrane to the plasma membrane.Endocytosis-exocytotic cycle must be under tight control.A macrophage ingests 3% of its plasma membrane per minute.EndocytosisPinocytosis cell drinking, 0.1~0.2umPhagocytosis cell eating 1.0um

Clathrin-coated pit

Rapidly return to the plasma membrane

Receptor mediated endocytosis #2 examplesFirst Cholesterol Cholesterol does not circulate in its free form, but as a component of 20nm spherical LDL particleLDL receptor in their plasma membrane, causes its uptake by receptor mediated endocytosis.Hypercholesterolema ; LDL receptors are not produced or defect the binding site

Receptor mediated endocytosis #2 examplesSecond-transferrin Serum glycoprotein involved in transport of iron from liver and intestine to other tissueApotransferrin+Fe2+ --> ferrotransferrinAll cells contain ferrotransferrin receptors.

Receptor recycleTranscytosisReceptor recycle

Selective and Non-selective vesicle transportSelective ; Clathrin-coated vesicle, TGN --> late endosomeNon-selective, constitutive ; coatmer coat, ER-->Golgi, between Golgi, Golgi --> Plasma membrane

proteinproteinenergy

Protein ; composed of seven COPsMonomeric G protein

Vesicle docking and fusionVesiclePlasma membrane synapsinSpectrin VAMPt-SNAREssynaptotagmin(syntaxin & SNAP25)Complex SNAP + NSF + ATP + Ca2+

VesiclePlasma membranesynapsinSpectrinVAMPt-SNAREssynaptotagmin(syntaxin & SNAP25)ComplexSNAP + NSF + ATP + Ca2+

Thank you for your attention ~