1. LIPID METABOLISM

2. SOURCES OF TRIACYLGLYCEROLS
Diet
De novo biosynthesis
Storage depots in adipocytes

3. DIGESTION, ABSORPTION, and TRANSPORTATION
Major problem: insolubility in aqueous environment
Solution: bile salts and formation of lipoproteins

4. BILE SALTS
Detergent substances synthesized in the liver and stored in the gallbladder
Essential in lipid digestion
Made up of a bile acid and an associated cation.
Bile acids are derived from cholesterol
Bile salts are amphipatic
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6. LIPOPROTEINS Several types classified according to their density
Lipoproteins in each class contain characteristic apoproteins and have distinct lipid composition
APOPROTEIN-a protein w/o its characteristic prosthetic group
Higher lipid abundance, lower density

7. Together, the lipoproteins help maintain in emulsified form some 500 mg of total lipid per 100 ml of human blood in the post absorptive state

8. TRANSPORT AND UTILIZATION
CHYLOMICRONS – from intestines to peripheral tissues (heart, muscle, adipose)
VLDL – for TAGs synthesized in the liver
IDL – derived from VLDL
LDL – principal form in which cholesterol is transported to tissues
HDL – returns excess cholesterol from tissues to liver for metabolism or excretion

10. PA NCREATIC LIPASE
an unusual calcium-requiring enzyme that catalyzes a reaction at an oil-water interface
Acts via an active site serine and an acyl-enzyme intermediate
Products of fat digestion comprise a mixture of glycerol, free fatty acids, monoacylglycerol, and diacylglycerol
Resynthesis of TAGs occurs in the ER and Golgi complex of mucosal cells
TAGs emerge into the lymph system complexed with protein to form the lipoproteins called CHYLOMICRONS

11. MOBILIZATION OF FAT
The capacity to store fat is unlimited but the release of fat from storage depots is controlled hormonally
The first step of mobilization is the hydrolysis of TAG into glycerol and FFA
This step is controlled by a cascade involving cAMP
ACTIVATORS: epinephrine (stress) or glucagon (fasting)

12. MOBILIZATION OF FAT
Hormone-receptor interaction activates adenylate cyclase which in turn activates cAMP.
cAMP activates protein kinase A phosphorylates triacylglycerol lipase (hormone-sensitive lipase) which catalyzes the hydrolytic release of FA from C1 or C3
The TAG hydrolysis products exit the adipocyte by passive diffusion, goes to the blood plasma, and bind to albumin
Each molecule of albumin can bind up to 10 molecules of FFA

13. FATTY ACID ACTIVATION and TRANSPORT
Fatty acids are present in the cytosol
FA oxidation occurs in the inner mitochondria
Fatty acyl-CoA is the active form
The reaction is catalyzed by fatty acyl CoA synthetase which are length-specific
Activation is a two-step process (outer mitochondria)

15. BETA-OXIDATION PATHWAY
Each series of steps acetyl CoA is produced
4 steps per cycle
The acetyl CoA produced will enter the Kreb’s cycle, where it is oxidized into CO2