Elino, M.M.H.BSBio 22A Biochemistry

PLASMA LIPID LEVELS

-FATS and PHOSPHOLIPIDS are emulsified and hydrolyzed into fatty acids and glycerol.

-Fatty acids are usually ingested as triglycerides, which cannot be absorbed by the intestine. They are broken down into free fatty acids and monoglycerides by pancreatic lipase

ABSORPTION OF FATS

The digestion of fats takes place primarily in the small intestine, with hydrolysis yielding fatty acids and glycerol.

Fat/ Phospholipids + H2O pancreatic lipase Fatty acids + glycerol

The products of fat digestion pass through:

Lacteals of villi Lymphatics Thoracic duct Bloodstream

Liver

Bloodstream

All Parts of the body

In the liver, some fats are changed into phospholipids, so the blood leaving the liver contains both fats anf phospholipids. These phospholipids, such as sphingomyelin and lecithin are necessary for the formation of nerve and brain tissues. Lecithin are also involved in the transportation of the fat to tissue. Cephalin, another phospholipid is involved in the normal clotting of the blood. From the liver some fat goes to cells, where it oxidized to furnish heat and energy. The fat in excess of what the cells need is stored as adipose tissue.

OXIDATION of FATS

Oxidation of fats involves the oxidation of two products of the hydrolysis:

the oxidation of GLYCEROL and FATTY ACIDS

Oxidation of glycerol is metabolized through the carbohydrate sequence.

Lipids Hydrolysis Glycerol Gluconeogenesis Glucose Pyruvic Acid Acetyl CoA

KREBS CYCLE

OXIDATIVE PHOSPHORYLATION

Production of ATPs

Oxidation of Fatty Acids

Fatty Acid Acetyl CoA

KREBS CYCLE

OXIDATIVE PHOSPHORYLATION

Production of ATPs

There are several theories about oxidation of fatty acids. The original one, proposed by knoop in 1905 and still prefered today, the β-oxidation theory. It involves the oxidation of the second carbon atom from the acid end, β-carbon . And so, it removes two carbon atoms at a time from the fatty chain. That is, an 18-carbon atom fatty acid is oxidized into 16 then to 14 and so on and so forth until the oxidation is complete.

For the unsaturated fats, they must be first reduced by some of the dehydrogenases found in cells. Then they can follow the fatty acid cycle for oxidation.

ENERGY PRODUCED by Oxidation of Fatty Acids

The oxidation of 1g of fat produces more than twice as much energy as the oxidation of 1g of carbohydrate.

1 Acetyl CoA = 12 ATPs

Palmitic Acid = 16-carbon molecule = 8 Acetyl CoA = 96 ATPs

Palmitic Acid = 7 FADH2 + 7 NADH ( FADH2 = 2 ATPs ; NADH = 3 ATPs)

7 FADH2 (14 ATPs ) + 7 NADH (21 ATPs) = 35 ATPs

Initial activation of Fatty Acid = -2 ATPs

One molecule of Palmitic Acid = 96+35-2 = 129 ATPs

Considering each mole of ATP as requiring 7.6 kcal for formation, 129 x 7.6 kcal, or 980 kcal is needed. The theoretic yield from I mol of palmitic acid is 2340 kcal, so that the efficiency of conversion is 980/2340, or 42 %, with the remainder of the energy being produced by heat. ( Other fatty acids and glycerol are also oxidized, so the net result is that fats produce more energy than do carbohydrates )

END…