metabolism
20.8 End-of-Chapter Material Chapter Summary To ensure that you understand the material in this chapter, you should review the meanings of the bold terms in the following summary and ask yourself how they relate to the topics in the chapter. Metabolism is the general term for all chemical reactions in living organisms. The two types of metabolism are catabolismthose reactions in which complex molecules carbohydrates, lipids, and proteins are broken down to simpler ones with the concomitant release of energyand anabolismthose reactions that consume energy to build complex molecules. Metabolism is studied by looking at individual metabolic pathways, which are a series of biochemical reactions in which a given reactant is converted to a desired end product. The oxidation of fuel molecules primarily carbohydrates and lipids , a process called respiration, is the source of energy used by cells. Catabolic reactions release energy from food molecules and use some of that energy for the synthesis of adenosine triphosphate ATP ; anabolic reactions use the energy in ATP to create new compounds. Catabolism can be divided into three stages. In stage I, carbohydrates, lipids, and proteins are broken down into their individual monomer unitssimple sugars, fatty acids, and amino acids, respectively. In stage II, these monomer units are broken down by specific metabolic pathways to form a common end product acetyl-coenzyme A CoA . In stage III, acetyl-CoA is completely oxidized to form carbon dioxide and water, and ATP is produced. Saylor URL: http://www. saylor. org/books.