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1. DR. TISCHLER ?LIPID TRANSPORT
2. OBJECTIVES List the lipid components of the diet.
Describe the five steps of digestion and absorption of lipids including the important enzymes and location where each step occurs.
Describe the general structure of a lipoprotein
Name the 4 main classes of lipoproteins and
a) indicate whether each is in the exogenous or the endogenous system.
b) identify the major lipid component in each.
c) describe their lipid-transport functions.
d) list their key apoproteins and the functions of these apoproteins
3. OBJECTIVES Discuss the function of lipoprotein lipase.
Outline the steps in the processing of:
a) chylomicrons from their synthesis in the intestinal cell to the delivery of cholesterol in chylomicron remnants to the liver.
b) VLDL from its synthesis in the liver to the delivery of cholesterol to cells via the low-density-lipoprotein (LDL) receptor including the cellular uptake and processing of cholesterol via LDL.
Describe how defects in the LDL receptor are associated with familial hypercholesterolemia and atherosclerosis
4. Fat (lipid) makes up 37% of the calories in the American diet
Fat is energy rich and provides 9 kcal/gm
Dietary lipids are 90% triacylglycerols, but also include cholesterol esters, phospholipids, essential unsaturated fatty acids and fat soluble vitamins
Normally essentially all (98%) of the fat consumed is absorbed, and most is transported to adipose for storage.
5. STEP 3
Liver releases bile acids to solubilize lipid products in mixed micelles STEP 2
phospholipase A2 Lipids:
Phospholipids pancreas liver STEP 4
Lipids absorbed from micelles into epithelial cells STEP 5
Chylomicrons form and travel through lymphatics Figure 1 Five steps of lipid digestion and absorption small intestine stomach
6. Table 1. Steps of lipid digestion and absorption
7. Figure 2. Model of low density lipoprotein. Other lipoproteins have a similar structure differing in the core content of lipid and the type of apoproteins on the surface of the molecule
8. Table 2. The major classes of lipoproteins and their relative content of triacylglycerol, cholesterol and protein
9. LIVER ApoB48
helps with chylomicron non-hepatic tissues Figure 3. Exogenous pathway of lipid transport. Chylomicrons carry dietary fatty acids to tissues and remnants take cholesterol to the liver chylomicron interacts with lipoprotein lipase removing FFA Lymph system:
10. LIVER HDL scavenges cholesterol Figure 4. Endogenous pathway of lipid transport. non-hepatic tissues VLDL interacts with LPL
Produce LDL LDL into cell delivers cholesterol
11. free pool of
CE endocytosis late endosome CE?cholesterol
B100 ? a. acids NPC-1 mediated transfer Golgi
ACAT CE CE CE stored in droplets ooo clathrin-
coated pit ooo vesicle Recycling of clathrin transport vesicle- lysosome fuse forming late endosome
Ligand/receptor dissociate in sorting endosome lysosome Figure 5. Steps in the cellular uptake of cholesterol via the LDL receptor. Recycling of clathrin and receptor
12. Table 3. Summary of lipoprotein functions
13. Table 4. Summary of apoproteins and their characteristics