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What are the classes of endocytic activities seen in animal cells, and in general how do they differ? What about any such activities in prokaryotic cells?phagocytosis: engulf particle using pseudophobia and enclosing it in vacuole, specific cell surface determines uptakepinocytosis: vesicles spontaneously and constitutively form, smaller scale than phagocytosisreceptor-mediated endocytosis: plasma membrane contains coated pits that bind extracellular molecules (ex. hormone reuptake)Outline the typical fate of a bacterium internalized by a macrophage.blue pathway: early endosome/secretory vesicle/late endosome -> golgi -> ER green pathway: early endosome -> late endosome -> lysosome (digests vesicle contents)red pathway: ER -> golgi -> secretory vesicle/late endosome -> lysosome/early endosome-> late endosome -> lysosomethere is a lot of traffic of these vesicles, theme is that they moved because they are attached to motor proteins on microtubules, part of specificity of vesicle direction is determined by the types of snares it mayhave, these snares provide adapters that link vesicles to target membraneWhat are lysosomes? What are the properties of their enzymes? List five lysosomal enzymes and indicate the classes of substrates they act upon and the reactions they would catalyze.- membrane surrounded compartments, hydrolytic enzymes within, degarde internalized mat., will not degrade each other or membranes- work in optimal pH of 5.4 acidic, and is protective in case contents leak out into cell (which has pH of 7.2) enzymes will be sluggish and not cause accidental damage - ATP is used to pump in H+ and make acidic pH● nuclease- break down nuclear membrane● protease- general protein digestion● glycosidase- breaks down bond between a sugar/alcohol or sugar/sugar● lipases- breaks down fats● phosphatases- removes a phosphate group● sulphatases- break down sulfate ester bond● phospholipases- break down phospholipidsGive an example of a lysosomal disorder by indicating the nature of the deficit and the resulting outcome.lysosome degrade matrix between cells, and cartilage, needed for development when the cells and tissues must be remodeled Hurler’s syndrome lacks a lysosomal enzyme, infant inherited 2 defective genes from parents- alpha-L-iduronidase deficiency, cannot degrade dermatan and heparan sulphate which must occur for proper developmental processes- enlarged liver, gargoyle like features, heart failure, mental retardation, short life spanGive examples of specific pathogens that block their own neutralizations in human hosts and manage to evade the host's immune responses. Describe what happens in each case.Outline the events involved in the uptake of iron and of LDL from the circulation by receptor- mediated endocytosis. You should include the details on how the ligands get internalized into cells and the proteins involved and their fates.receptor mediated endocytosis in cholesterol is a disorder that leads to elevation in cholesterol levels, involves problems with LDL receptor so that the receptor cannot aggregate at these sitesuptake of ironiron is needed for oxygen binding in hemoglobinheme is associated with ironiron is needed in many cells but is very toxic 1. iron binds to transferrin (Tf) a small protein in circulation 2. Tf with attached iron bind to TfR (receptor on plasma membrane) pH 7.23. TfR + iron + Tf are engulfed by receptor-mediated endocytosis via coated pits4. internalized into vesicles move to the early endosome pH 5.5 due to proton pump5. iron loses its affinity to Tf due to pH changes6. iron is reduced (from Fe III -> Fe II)7. Tf and TfR go into recycling endosome to be released to the plasma membrane8. reduced iron is used in cell (hemoglobin or ferritin)Describe the composition of the coat on coated vesicles and pits involved in endocytic activities: triskelion, clathrin, adaptin, receptors, ligands and the orientations of these components in the membranes.coated pit: picks up substances, neck region forms and buds off, use surface protein to trap ligands, peripheral proteins are swept into the sinks and are internalized into vesicletwo types of receptors and ligands1. housekeeping receptors: proteins on cell surface that bring substances that cells require, ex. pick up iron, receptors are saved and recycled to membrane 2. signaling receptors: hormones responses may only be needed for a certain time and may be degraded after usetryskelion: 3 legged structure each tryskelion is clathrin protein made of 3 heavy and 3 light chains, polyhedral structures in coated vesicles, leg of one interacts with leg of other to form this coat, clathrin will spontaneously form these coats, low energy state 2 molecule types: heavy chains (180,000 dalton) and light chains (25,000 dalton)big variety of triskelions in different vesiclesadaptin: anchor clathrin to membraneAp1,2,3 etc. focus on Ap2 (found in plasma membrane)other forms found in golgi (Ap1)subunits: alpha beta mu and sigmabeta subunit anchors clathrin to membranealpha subunit is shown by this ear on other side, binds accessory proteins that add to curvature of the proteinreceptor being attached to coated vesicles typically has cytoplasmic segment that will bind to adaptor protein, which holds it in placeWhat is the role of dynamin in vesicle budding? How does the presence of gamma-S-GTP affect the action of the protein?dynamin: assembled at site where membranes are buddingfor coated vesicles (different types of dynamin help when cell is dividing by splitting mitochondria) energy comes from GTPhelical structure around neck which gets thinner and eventually buds off as GTP is usedif GTP is there it is hydrolyzedif GTP gamma S (sulfur instead of phosphate) then cannot be hydrolyzed by dynamin- so it freezes the dynamin structure, continuous helices of dynamin elongatedGive is the composition of LDL particles - Be specific and detailed!LDL: monolayer of phospholipid and cholesterol molecules, core of the LDL consists of cholesterol with attached fatty acids, and 1 molecule of protein apoB100Describe the endosomal compartments and outline some of the activities associated with the sorting and intracellular digestions that take place in those compartments (give examples from LDL uptake).cholesterol is very insoluble so must be packaged in particle- low or high density lipoproteinin animal cells plasma membranein nucleus for production of steroid hormoneswhen cholesterol levels are low in cell:-


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UMD BSCI 330 - Lecture notes

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