Fundamentals of Biochemistry Third Edition Fundamentals of Biochemistry Third Edition Chapter 20 Lipid Metabolism Chapter 20 Lipid Metabolism Copyright © 2008 by John Wiley & Sons, Inc. Donald Voet Judith G. Voet Charlotte W. Pratt

Triglycerides Major fuel source in humans Digestion occurs at lipid-water interfaces

Lipases and fatty acid binding proteins aide in absorption and digestion of triglycerides

Fatty acids are still insoluble and are transported by lipoprotein complexes Chylomicrons – intestinal synthesized, dietary lipids VLDL, IDL, LDL – liver synthesized, endogenous transport from liver HDL – transport cholesterol back to liver

Lipid Transport

Receptor Mediated Endocytosis of LDL

Fatty Acid Activation Fatty acids are transported via serum albumin Coenzyme A must be attached to the fatty acid before it can be oxidized

The activated fatty acid must be transported across the mitochondrial membrane

Highly Exergonic B-oxidation makes: FADH 2 ; NADH; and acetyl-CoA Acetyl-CoA makes: FADH 2 ; 3 NADH; 1 GTP C 16 would be 7 rounds & 8 acetyl-CoA 15 FADH2 (1.5) = 22.5 ATP 31 NADH (2.5) = 77.5 ATP 8 GTP = 8 GTP Total = 108 ATP Used to for priming = 106 ATP Glucose = ATP = 0.18 ATP/g C16 = ATP = 0.41 ATP/g Saturated Fatty Acids

Unsaturated Fatty Acids

Odd chain fatty acids end in propionyl-CoA, which is converted to Succinyl-CoA for TCA

Synthesis or breakdown of ketone bodies

Must get acetyl groups out of the mitochondria

First Committed Step of Fatty Acid Biosynthesis

Synthesis requires a carrier

Synthesis of Palmitate uses: 8 Acetyl-CoA 14 NADPH 7 ATP Completely saturated fatty acid

Desaturases make unsaturated fatty acids Fatty acids can be elongated

Synthesis of triglycerides

Figure 20-31