Chapter 17 The oxidation of fatty Acids
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 vs18 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
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 special organs(e.g, liver)
• 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 special organs (e.g., liver)
2. Diet triacylglycerols are emulsified and absorbed by the intestine Bile salts(e.g, 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)
2. Diet triacylglycerols are emulsified and absorbed by the intestine • Bile salts (e.g., 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 b 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 tissues after being packed with apolipoproteins
• 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 tissues after being packed with apolipoproteins
Fats ingested in die The emulsification, absorption and transport of diet triacylglyc 6 Fatty acids are oxidized nel or reesterified Gallbladder Myocyte or co Smal intestine ⑦ Fatty acids enter cells ① Bile salts emulsify dietary fats in the small intestine, forming Lipoprotein lipase ⑥Li activated by apoC-ll in the capillary. ② Intestinal lipases releases fatty acids and degrade triacylglycerols glycerol Intestinal ⑤ Chylomicrons move the lymphatic Apoc-Il products are taken up by the wn 6 Fatty acids and other breakdo Chylomicron intestinal mucosa and converted into triacylglycerol O Triacylglycerols are incorporated, with cholesterol and apoproteins into chylo
The emulsification, absorption and transport of diet triacylglycerol
C-C C-C C—NCH2-C HO H 0- Glycocholate HO OH Glycocholate: the main bile salts that emulsifies macroscopic fat into microscopic micelles
Glycocholate: the main bile salts that emulsifies macroscopic fat into microscopic micelles
Apoproteins A chylomicron particle B-48 C-II c-ll Phospholipids Cholesterol Triacylglycerols and cholesteryl esters
A chylomicron particle
3. Mobilization of stored triacylglycerols in adipocytes needs hormone to signal the demand The hormones epinephrine and glucagon, signaling a lack of glucose in the blood, will bind to receptors on adipocyte surface and activate the triacylglycerol lipase via phosphorylation Fatty acids released are carried to energy-demanding tissues(e.g. skeletal muscle, heart, and renal cortex) via the 62 kD monomeric serum albumin(each binding about 10 fatty acids)
3. Mobilization of stored triacylglycerols in adipocytes needs hormone to signal the demand • The hormones epinephrine and glucagon, signaling a lack of glucose in the blood, will bind to receptors on adipocyte surface and activate the triacylglycerol lipase via phosphorylation. • Fatty acids released are carried to energy-demanding tissues (e.g., skeletal muscle, heart, and renal cortex) via the 62 kD monomeric serum albumin (each binding about 10 fatty acids)
The glycerol molecule generated can be converted to glycolytic intermediate glyceraldehyde 3-phosphate by the successive action of glycerol kinase, glycerol 3-phosphate dehydrogenase, and triose phosphate somerase
• The glycerol molecule generated can be converted to glycolytic intermediate glyceraldehyde 3-phosphate by the successive action of glycerol kinase, glycerol 3-phosphate dehydrogenase, and triose phosphate isomerase
