Digestion and Transport of Dietary Lipids

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Lecture 49

cholesterol

has 27 carbons, 1 hydroxy group, it is a flat molecule that is very hydrophobic and converts to bile acids

bile acids

2 additional hydroxy groups and a COOH group added to the cholesterol, hydrophilic on one side and hydrophobic on the other (amphipathic) and is kinked

NPC1L1

dietary cholesterol is absorbed into enterocytes by diffusion and by this, a cholesterol transporter

ABCA1

cholesterol effluxes out of enterocytes via this transporter

ABCG5/ABCG8

plant sterols are excreted via these transporters - deficiency causes sitosterolemia

triglycerides

the major fat in the human diet consisting of three fatty acids esterified to a glycerol backbone - produced in the SER of intestinal epithelial cells

2-monoacylglycerol

the main route for degradation of triglycerides involves hydrolysis to fatty acids and this

bile salts

derived from cholesterol - emulsifies fats in the small intestine - synthesized in the liver, stored in the gallbladder and secreted into the intestinal lumen - act as detergents, binding to the globules of fat

cholecystokinin

secreted by the intestine, signals the gallbladder to contract and release bile acids, and the pancreas to release digestive enzymes

bile acids

activate pancreatic lipases

colipases

increase lipase activity to digest triglycerides to monoacylglycerol and free fatty acids

cholesterol esterases

hydrolyze cholesterol esters to free cholesterol and fatty acids

micelles

bile acids emulsify fatty acids and monoacylglycerol to form ____ - must reach 5-15 mM CMC to form

chylomicrons

contain 85% TG, Apo B-48, cholesterol esters, phospholipids, and fat-soluble vitamins - assembled in both ER and golgi complex and secreted into lymph

ApoB48

synthesized in the rough ER

nascent CMs

secreted into the lymphatic system and enter the blood through the thoracic duct - receive ApoCII and ApoE from HDL to form mature CM

ApoE

recognized by membrane receptors, LDL receptor-related proteins

ApoCII

activates LPL located on the surface of the capillary endothelial cells in muscle and adipocytes, and digest TG to release free FAs from CM and VLDL

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