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Lipids • Fatty Acids (FA) and Triglycerides (TG) – high density energy store • Phospholipids – major components of membranes – contain precursors of many biologically active substances, such as: prostaglandins, thromboxane, inositol trisphosphate – modulate the activities of membrane enzymes and transporters • Cholesterol (not really a lipid, but lipid soluble and lipid derived) – prominent part of membranes, control fluidity and protein function – precursor for bile acids and steroid hormones – most cells can synthesize it from Acetyl CoA; liver makes most of it Copyright © 2006 by Elsevier, Inc. H2C-OH HO-CH H2C-OH O H3C (CH2)16 C OH 3 of these fatty acids (stearic acid) + O H3C (CH2)16 C-O-CH2 O H3C (CH2)16 C-O-CH2 O H3C (CH2)16 C-O-CH2 Copyright © 2006 by Elsevier, Inc. Glycerol a triglyceride (tristearin, p. 840) H2C-OH HO-CH H2C-OH Glycerol H 2H2C-OPO3 Glycerol-3-P O C HO-CH 2H2C-OPO3 Glyceraldehyde-3-P Copyright © 2006 by Elsevier, Inc. H2C-OH HO-CH H2C-OH O C 2H2C-OPO3 Dihyroxyacetone-P The Liver & Lipids • oxidize triglycerides (fatty acids) for energy • production of ketone bodies from triglycerides (FA) – exported to other cells as energy source (Acetyl CoA) • synthesize triglycerides, mainly from glucose – some from amino acids as well • synthesize other lipids, mainly phospholipids and cholesterol, from fatty acids • de-saturate fatty acids (most FA in TG’s in adipose tissue are saturated) – saturated means no double bonds, chock full o’ hydrogens Copyright © 2006 by Elsevier, Inc. Beta Oxidation of Fatty Acids Downloaded from: StudentConsult (on 4 March 2009 04:13 PM) Copyright © 2006 by Elsevier, Inc. © 2005 Elsevier Ketone Bodies FA CoA Ox. Pyruvate Acetyl CoA Acetyl CoA Acetoacetyl CoA Citrate HMG CoA Succ. CoA NADH Oxaloacetate NADH Malate acetoacetate Succinate NAD+ CO2 -3-hydroxybutyrate acetone Copyright © 2006 by Elsevier, Inc. mitochondria Problem Solving… • What would be the net ATP gain from a triglyceride consisting of three palmitic acid chains (these are 16-C fatty acids…)? Copyright © 2006 by Elsevier, Inc. • Glycerol enters glycolysis as glyceraldehyde-3phosphate – worth ~ 36 ATP • Palmitic acid – 16 carbons = 8 acetyl-CoA, 7 NADH, & 7 FADH2 • 8 acetyl-CoA = 12 ATP each = 96 ATP • 7 NADH = 3 ATP each = 21 ATP • 7 FADH2 = 2 ATP each = 14 ATP • Palmitic acid then worth 131 ATP – but 2 ATP equivalent required to start beta-oxidation, so actually worth approximately 129 ATP. • Three palmitic acid chains in a triglyceride – 129 x 3 = ~ 387 ATP, plus ~ 36 ATP from glycerol = ~ 423 ATP Copyright © 2006 by Elsevier, Inc.