BE230_Lecture_10 - BE230 Lecture 12 ENDOCYTOSIS Bulk phase...

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Unformatted text preview: BE230 Lecture 12 ENDOCYTOSIS Bulk phase endocytosis Non specific uptake of extracellular fluids Receptor-mediated endocytosis Uptake of specific extracellular macromolecules that bind to receptors on external surface of plasma membrane 50% surface membrane can be internalised in 30minutes! The endocytic pathway Involves early endosomes (nearer plasma membrane) and late endosomes (nearer nucleus) Acidic due to H + ATPase proton pump in membrane Materials get sorted in early endosomes i.e receptors sent back to plasma membrane Materials within sent to late endosomes Directed to lysosome Receptor-mediated endocytosis Cells have receptors for uptake hormones Growth factors Enzymes Plasma proteins Receptors collect in speed areas of plasma membrane called coated pits LDLs and cholesterol metabolism Best understood example of receptor mediated endocytosis LDL cholesterol 1500 cholesteryl ester molecules Single layer of phospholipids, free cholesterol Single molecule of apolipoprotein B-100 Binds specifically to LDL receptors on surfaces of cells Composition & Density of Human Lipoproteins Chylomicron VLDL IDL LDL HDL Density (g/ml) <0.95 0.95-1.006 1.006- 1.019 1.019- 1.063 1.063 1.210 Diam (nm) 75-1200 30-80 25-35 18-25 5-12 Protein (%) 1-2 10 18 25 33 TG (%) 83 50 31 10 8 C & CE (%) 8 22 29 46 30 PL (%) 7 18 22 22 29 Apo Chylo: AI, AII, B48, CI, CII, CIII VLDL:B100, CI,CII,CIII, E IDL:B100, CI,CII,CIII, E LDL: B100 HDL:AI,AII, CI, CII, CIII, D, E Apoproteins Generalised Structure Spherical 10-1000nm diameter neutral lipid core of TG and or CE Around core is layer of protein, PL, C oriented with polar portions exposed to surface of lipoprotein 9 apoproteins several enzymes cholesteryl ester transfer ptotein LDL particle LPs made in Endoplasmic Reticulum of Liver & Intestine Cholesterol + acyl Co A------->Cholesteryl ester storage form of cholesterol ENZYME: acyl-Co: cholesterol acyltransferase (ACAT) LOCATED on cytosolic surface of liver ER apoproteins synthesised on ribosomes Chylomicrons Produced by intestinal cells secreted into lymphatic capillaries enter bloodstream at large subclavian vein bypass liver VLDL & HDL Produced in liver cell CMs & VLDLs transport C & TG to other tissues Triglyceride-rich particles degraded by lipoprotein lipase extracellular enzyme that is most active within capillaries of adipose tissue, heart muscle, skeletal muscle, lactating mammary gland LPL activated by CII (CMs, VLDL) supplies heart and adipose tissue with fatty acids derived from these LPs used for energy or stored...
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BE230_Lecture_10 - BE230 Lecture 12 ENDOCYTOSIS Bulk phase...

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