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25.1 Digestion of Triacylglycerols

25.2 Oxidation of Fatty Acids

25.3 ATP and Fatty Acid Oxidation

Chapter 25 Metabolic Pathways for Lipids and Amino Acids

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Digestion of Triacylglycerols

In the digestion of fats (triacylglycerols): Bile salts break fat globules into micelles in

the small intestine. Pancreatic lipases hydrolyze ester bonds to

form monoacylglycerols and fatty acids, which recombine in the intestinal lining.

Lipoproteins form and transport triacylglycerols to the cells of the heart, muscle, and adipose tissues.

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Digestion of Triacylglycerols

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Fat Mobilization

Fat mobilization: Breaks down

triacylglycerols in adipose tissue to fatty acids and glycerol.

Fatty acids are hydrolyzed initially from C1 or C3 of the fat.

Triacylglycerols + 3H2O Glycerol + 3Fatty acids

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Fatty Acid Activation

Fatty acid activation: Allows the fatty acids in the cytosol to enter the

mitochondria for oxidation. Combines a fatty acid with CoA to yield fatty

acyl CoA that combines with carnitine.

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Fatty Acid Activation

Fatty acyl-carnitine transports the fatty acid into the matrix.

The fatty acid acyl group recombines with CoA for oxidation.

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Fatty Acid Activation Fatty acid activation is complex, but it

regulates the degradation and synthesis of fatty acids.

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Beta-Oxidation of Fatty Acids

In reaction 1, oxidation: Removes H atoms from the

and carbons. Forms a trans C=C bond. Reduces FAD to FADH2.

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Beta-Oxidation of Fatty Acids

In reaction 2, hydration: Adds water across the

trans C=C bond. Forms a hydroxyl

group (—OH) on the carbon.

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Beta ()-Oxidation of Fatty Acids

In reaction 3, a second oxidation:

Oxidizes the hydroxyl group.

Forms a keto group on the carbon.

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Beta ()-Oxidation of Fatty Acids

In Reaction 4, acetyl CoA is cleaved:

By splitting the bond between the and carbons.

To form a shortened fatty acyl CoA that repeats steps 1 - 4 of -oxidation.

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Beta ()-Oxidation of Myristic (C14) Acid

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Beta ()-Oxidation of Myristic (C14) Acid (continued)

7 Acetyl CoA

6 cycles

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Cycles of -Oxidation

The length of a fatty acid: Determines the number of oxidations and The total number of acetyl CoA groups.

Carbons in Acetyl CoA -Oxidation CyclesFatty Acid (C/2) (C/2 –1)12 6 514 7 616 8 718 9 8

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-Oxidation and ATP

Activation of a fatty acid requires: 2 ATP

One cycle of oxidation of a fatty acid produces: 1 NADH 3 ATP 1 FADH2 2 ATP

Acetyl CoA entering the citric acid cycle produces: 1 Acetyl CoA 12 ATP

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ATP for Lauric Acid C12

ATP production for lauric acid (12 carbons):Activation of lauric acid -2 ATP

6 Acetyl CoA6 acetyl CoA x 12 ATP/acetyl CoA 72 ATP

5 Oxidation cycles 5 NADH x 3ATP/NADH 15 ATP5 FADH2 x 2ATP/FADH2 10 ATP

Total 95 ATP