fat and lipids metabolism

Fat and lipid metabolism
University of Babylon
College of pharmacy
Biochemistry
Second semester 3rd class
Dr. Abdulhussien Aljebory
2015
1 g of triacylglycerols stores more than six times as much energy as a 1 g of glycogen
Glycogen reserves are depleted in 12 to 24 hours after eating, triacylglycerols within several weeks.
Fat breakdown about 50 % of energy in liver, kidney and skeletal muscles up to 95 % of energy cardiac muscle
Fats are the major source of energy for: fasting animal organism in diabetes
Fatty acids and glycerol - substances that are directly used as a fuel by mammalian organisms.
Fatty acids (FA) and glycerol for metabolic fuels are obtained from triacylglycerols:
(1) In the diet
(2) Stored in adipocytes (fat storage cells)
Free fatty acids occur only in trace amounts in cells
For supplying of fatty acids as a fuel for organism, the triacylglycerols have to be digested
DIGESTION OF DIETARY LIPIDS
Lipids in diet: ? triacylglycerols ? phospholipids ? cholesterol
Digestion – in small intestine.

Enzyme – pancreatic lipase.

Lipase catalyzes hydrolysis at the C1 and C3 positions of TGs producing free fatty acids and 2-monoacylglycerol.
Colipase – protein which is present in the intestine and helps bind the water-soluble lipase to the lipid substrates.
Colipase also activates lipase.
Bile salts (salts of bile acids) are required for lipids digestion. Bile salts are synthesized in the liver from cholesterol.
Taurocholate and glycocholate - the most abundant bile salts.
Amphipathic: hydrophilic (blue) and hydrophobic (black)
TGs are water insoluble and lipase is water soluble.
Digestion of TGs takes place at lipid-water interfaces.
Rate of digestion depends on the surface area of the interface.
Bile salts are amphipathic, they act as detergent emulsifying the lipid drops and increasing the surface area of the interface.
Dietary phospholipids are degraded by phospholipases
Phospholipases are synthesized in the pancreas.
Major phospholipase is phospholipase A2 (catalyses the hydrolysis of ester bond at C2 of glycerophospholipids and lysophosphoglycerides are formed).
Lysophospho-glycerides are absorbed and in the intestinal cells are reesterified back to glycero-phospholipids.