bio chemistry lecture 8

1. METABOLISM OF LIPIDS
• Fatty acid oxidation biosynthesis and metabolism of
Triacylglycerols
• Metabolism & Clinical Significance of Lipoproteins

2. LIPIDS
• A heterogeneous group of water-insoluble (hydrophobic) organic
molecules
• Insolubility in aqueous solutions
• A major source of energy
FUNCTIONS
• Regulatory or coenzyme functions
• Fat-soluble vitamins
• The prostaglandins and steroid hormones
• Deficiencies or imbalances
(Compartmentalized)
Hydrophobic barrier
(Homeostasis)
(Atherosclerosis, diabetes & obesity)

3. Digestion of Lipids

4. STRUCTURE OF FATTY ACIDS
• A hydrophobic hydrocarbon chain with a terminal carboxyl
group
• At physiologic pH the terminal carboxyl group (–COOH)
ionizes, becoming –COO–.
• Amphipathic nature
• LCFAs
• Transported in the circulation in association with protein
• 90% of the fatty acids found in plasma
• Unesterified (free) fatty acids
The hydrophobic portion is predominant
(Fatty acid esters (primarily TAG,
cholesteryl esters, and phospholipids)
Transported in the circulation in association with albumin

5. BIOSYNTHESIS OF FATTY ACIDS
• A large proportion of the fatty acids
• Carbohydrates and protein obtained from the diet
• In adult humans primarily in the liver and lactating mammary
glands and, to a lesser extent, in adipose tissue.
• This cytosolic process incorporates carbons from acetyl
coenzyme A (CoA) into the growing fatty acid chain
Supplied by the diet.
Converted to fatty acids(stored as tags)
Fatty acid synthesis occurs
Liver
Lactating mammary glands
Adipose tissue
Adenosine triphosphate (ATP), NADH

6. Storageof fatty acids as components of
triacylglycerols
Structure
The three fatty acids
Carbon 1 : Typically saturated
Carbon 2 : Typically unsaturated
Carbon 3 :
Not of the same type

7. OXIDATION OF FATTY ACIDS
• Fatty acids stored in WAT(white adipose tissue), in the form of
neutral TAG, serve as the body’s major fuel storage reserve
• The yield from the complete oxidation of fatty acids to CO2
and H2O is 9 kcal/g fat
• Release of fatty acids from fat
• β-Oxidation of fatty acids
Hydrolytic release of fatty acids and glycerol
(lipases)
The major pathway for catabolism of fatty acids is a
mitochondrial pathway called β oxidation

8. β-Oxidation of fatty acids

9. PLASMALIPOPROTEINS
• LIPOPROTEINS :
PLASMA LIPOPROTEINS
• Chylomicrons
• Very-lowdensity lipoproteins (VLDLs)
• Low-density lipoproteins (LDLs)
• High-density lipoproteins (HDLs)
Spherical macromolecular complexes
of lipids and specific proteins
(apolipoproteins)
Differ in lipid and protein
composition, size, density

10. Composition& Functions of plasma
lipoproteins
• Structure of Lipoprotein
• Lipoproteins function
• Transport
• In humans
Plasma & the tissues
The transport system is less perfect
Gradual deposition of lipid (especially cholesterol) in
tissues
Plaque formation
Atherosclerosis

11. Metabolism of Lipoprotein
• Metabolism of chylomicrons
• Metabolism of very-low-density lipoproteins (VLDL)
• Metabolism of low-density lipoproteins (LDL)
• E. Metabolism of high-density lipoproteins (HDL)
In intestinal mucosal cells and carry dietary
(exogenous) TAG, cholesterol, fat-soluble
vitamins, and cholesteryl esters
90% of
the
lipids
Produced in the liver
Composed predominantly of endogenous TAG
60%
Less TAG than their VLDL predecessors and have a high
concentration of cholesterol and cholesteryl esters
Formed in blood by the addition of lipid to apo A-1, an apolipoprotein

12. Metabolism of Lipoprotein
Metabolism of chylomicrons Metabolism of VLDL

13. COMPOSITIONOFLIPOPROTEIN

14. Clinical Significance of Lipoproteins
Role of lipoprotein (a) in heart
• Elevated lipoprotein (a) slows the breakdown of blood clots
• Trigger heart attacks because it competes with plasminogen
for binding to fibrin
• Niacin reduces LP(a), as well as LDL-cholesterol and tags, and
raises HDL