Lesson # 19

1. Lesson # 19 Metabolism and Energetic 2 Chapter 25 Objectives: • 1- Describe the pathways involved in lipid metabolism. • 2- Define beta-oxidation. • 3- Discuss the use of proteins as an energy source..

2. The Citric Acid Cycle The function of the citric acid is to remove hydrogen atoms (and electrons) from organic molecules and to transfer them to coenzymes (NADH and FADH2). 2 H2O The coenzymes NADH and FADH2 remove hydrogen atoms and electrons from the substrate molecule and carry them to the Electron Transport System. NAD+ 2H2 + O2 ENERGY ATP

3. FADH2 NADH The Electron Transport System 3 2 ATP ATP

4. Beta-oxidation Glycolysis

5. Lipid Catabolism Intestinal cells absorb lipids from micelles, resynthesize triglycerides, and package triglycerides, cholesterol, and phospholipids into protein-coated chylomicrons. CHYLOMICRON

6. Lipid Transport and Distribution CHYLOMICRON Low Density Protein Very Low Density Protein They carry cholesterol to the peripheral cells. They carry triglycerides to the peripheral cells. VLDL VLDL LDL PERIPHERAL CELLS PERIPHERAL CELLS Lysosomal breakdown Lysosomal breakdown Used in synthesis of membranes, hormones, other materials. Used to produce ATP. Triglycerides Cholesterol

7. + Triglycerides Glycerol Fatty acids Lysosomal enzymes breakdown the triglyceride molecules into one glycerol molecule and tree fatty acids.

8. Beta-Oxidation VLDL Beta-oxidation is a sequence of reactions in which fatty acid molecules are broken down into two carbon fragments and FADH and NAD+ are reduced. Absorption through endocytosis FADH and NAD+ reduced in the Coenzyme A reaction produce 5 ATP molecules. CYTOSOL Lysosomal enzymes break down triglyceride molecules into one glycerol molecule and 3 fatty acids. Fatty acid (18-carbon) Glycerol Fatty acids are absorbed into the mitochondria. MITOCHONDRIA In the cytosol, the glycerol is converted to pyruvate through the glycolysis pathway. Fatty acid (18-carbon) Every fragment of two carbons yields 12 ATP molecules in the citric acid cycle and the electron transport chain. Pyruvate Coenzyme A Coenzyme A Fatty acid (18-carbon) – CoA The cell obtains 144 molecules of ATP from the breakdown of one 18 carbon fatty acid molecule. 12 5 Coenzyme A Acetyl- CoA Fatty acid (16-carbon) – CoA Acetyl CoA Citric acid cycle Electron transport system Coenzymes An enzymatic reaction then breaks off the first two carbons as acetyl-CoA while leaving a shorter fatty acid bound to the second molecule of coenzyme A. ATP ATP

9. Amino Acid Catabolism Proteins are an impractical source of quick energy: 1- Proteins are more difficult to brake apart than are complex carbohydrates and lipids. 2-One of the by-products, ammonium ions, is toxic to cells. 3- Proteins form the most important structural and functional components of any cell. Extensive protein catabolism threatens homeostasis at the cellular and systems levels. The first step in amino acid catabolism is the removal of the amino group (-NH2). The amino group is removed by: 1- Transamination The amino group is transferred to a keto acid 2- Deamination It is the removal of an amino group and a hydrogen atom in a reaction that generates an ammonium ion (NH4).

10. 1- Transamination It is broken down in the citric acid cycle. It is broken down in the citric acid cycle. It is a new amino acid that can be used in the synthesis of proteins 2- Deamination