文档介绍：Chapter 17 The Oxidation of Fatty Acids
1. The good and bad sides of using triacylglycerols as an energy storage
Highly reduced, more than twice as much energy as carbohydrates or proteins (~38 kJ/g vs ~18 kJ/g).
Highly hydrophobic: does not raise osmolarity of cytosol, nor add extra weight; but must be emulsified before digestion and transported by special proteins in blood.
Chemically inert: no undesired chemical reactions with other constituents; but must be activated (by attaching the carboxyl group to coenzyme A) to break the stable C-C bonds.
Fatty acids is a central energy source in animals (especially the liver, heart, and resting skeletal muscle), many protists, and some bacteria; the only energy source for hibernating animals and migrating birds; not a major energy source in plants.
Sources for cells to obtain fatty acids: diet; stored lipid droplets; synthesized from the excess carbohydrates and amino acids by some ans (., liver).
2. Diet triacylglycerols are emulsified and absorbed by the intestine
Bile salts (., taurocholate牛黄胆酸 and glycocholate甘胆酸), synthesized from cholesterol in liver, emulsifies macroscopic fat particles into microscopic mixed micelles for better lipase action and absorption.
Fatty acids generated from triacylglycerol (catalyzed by the intestinal lipase) diffuse into intestinal epithelial cells, be reconverted into triacylglycerol, and packed with cholesterol esters and specific apolipoproteins in chylomicrons (乳糜微滴).
Triacylglycerols are converted into fatty acids and glycerols in the capillaries by the action of lipoprotein lipases activated by apoC-II on chylomicrons, which in turn are absorbed mainly by adipocytes and myocytes for storage and energy consumption.
The leftover of the chylomicrons (containing mainly cholesterol and apolipoproteins) will be taken up by the liver by endocytosis; triacylglycerols will be used as the energy source for the liver cells, converted to ketone bodies or transported to adipose ti