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CHAPTER 7: CELLULAR RESPIRATION LECTURE OUTLINE 7.1 Metabolism The term catabolism is sometimes used to refer to the breaking down of molecules and the term anabolism is sometimes used to refer to the building up of molecules. Catabolism Our food contains three nutrients that our bodies break down and use as energy sources: carbohydrates, proteins, and fats. Anabolism Some of the building blocks for the synthesis of larger molecules come from intermediates in the pathways of catabolism. Catabolism also supplies the energy required for anabolism. Breathing, Eating, and Cellular Respiration Cellular respiration is the step-wise release of energy from molecules such as glucose, accompanied by the use of this energy to synthesize ATP molecules. The air we inhale when we breathe contains oxygen, and the food we digest after eating contains glucose, both substrates for cellular respiration. 7.2 Overview of Cellular Respiration The overall equation for cellular respiration shows the coupling of glucose breakdown to ATP buildup. NAD+ and FAD NAD+ and FAD are coenzymes of redox reactions. They pick up electrons (and their accompanying hydrogen nuclei) at specific enzymatic reactions and carry these electrons to the electron transport chain. Phases of Cellular Respiration The phases of cellular respiration include glycolysis, the preparatory reaction, the citric acid cycle, and the electron transport chain. 7.3 Outside the Mitochondria: Glycolysis Glycolysis is the breakdown of glucose to two pyruvate molecules. It takes place in the cytoplasm. Energy-Investment Steps Two ATP are used to activate glucose as glycolysis begins. Energy-Harvesting Steps Glycolysis breaks down glucose to two molecules of pyruvate, making ATP by substratelevel ATP synthesis. There is a net gain of 2 ATP from glycolysis. 7.4 Inside the Mitochondria Preparatory Reaction The preparatory reaction occurs inside the mitochondria. It produces the molecule from pyruvate that can enter the citric acid cycle. Citric Acid Cycle The citric acid cycle is a cyclical metabolic pathway located in the matrix of mitochondria. It oxidizes acetyl groups to carbon dioxide, making ATP by substratelevel ATP synthesis, and producing NADH + H+ and FADH2. Electron Transport Chain The electron transport chain is located in the cristae of the mitochondria. It is a series of carriers that pass electrons from one to the other, resulting in energy that is stored as a hydrogen ion gradient. Organization of Cristae The electron transport chain is located within the cristae of the mitochondria. The complexes in the chain establish a hydrogen ion gradient between the matrix and the intermembrane space. This gradient is used to synthesize ATP by chemiosmosis. Energy Yield from Cellular Respiration The complete breakdown of glucose results in 36 or 38 total ATP. Efficiency of Cellular Respiration Approximately 39% of the available energy is usually transferred from glucose to ATP. 7.5 Fermentation When oxygen is not available, cells turn to fermentation. During fermentation, glycolysis is followed by a reduction of pyruvate to lactate by NADH + H+. Advantages and Disadvantages of Fermentation Fermentation is essential to humans despite its low yield of ATP. However, lactate is toxic to cells. Energy Yield of Fermentation Fermentation produces only two ATP by substrate-level ATP synthesis.