Fig. 7-2a, p.108 a All carbohydrate breakdown pathways start in the cytoplasm, with glycolysis. b Fermentation pathways are completed in the semifluid matrix of the cytoplasm. c In eukaryotes, aerobic respiration is completed inside mitochondria. Fig. 7-2b, p.108 Cytoplasm glucose 2 ATP ATP GLYCOLYSIS 4 ATP (2net) ATP 2 NADH 2 pyruvate a The first stage, glycolysis, occurs in the cell’s cytoplasm. Enzymes convert a glucose molecule to 2 pyruvate for a net yield of 2 ATP. During the reactions, 2 NAD+ pick up electrons and hydrogen atoms, so 2 NADH form. Mitochondrion Krebs Cycle 6 ATP CO 2 ATP 2 8 NADH, 2 FADH2 ATP oxygen Electron Transfer Phosphorylation 32 ATP b The second stage, the Krebs cycle and a few steps before it, occurs inside mitochondria. The 2 pyruvates are broken down to CO2, which leaves the cell. During the reactions, 8 NAD+ and 2 FAD pick up electrons and hydrogen atoms, so 8 NADH and 2 FADH2 form. 2 ATP also form. c The third and final stage, electron transfer phosphorylation, occurs inside mitochondria. 10 NADH and 2 FADH2 donate electrons and hydrogen ions at electron transfer chains. Electron flow through the chains sets up H+ gradients that drive ATP formation. Oxygen Fig. 7-3, p.109 glucose 2 ADP (net) Glycolysis 2 pyruvate to second stage of aerobic respiration or another pathway 2 NADH to third stage of aerobic respiration or another pathway Fig. 7-4b, p.110 outer membrane (next to cytoplasm) glucose (glycolysis) 2 pyruvate OUTER COMPARTMENT inner membrane inner mitochondrial compartment outer mitochondrial compartment (in between the two membranes) a An inner membrane divides a mitochondrion’s interior into two compartments. The second and third stages of aerobic respiration take place at this membrane. 2 acetyl–CoA CO2 ATP NADH Krebs Cycle FADH2 INNER COMPARTMENT Breakdown of 2 pyruvate to 6CO2 yields 2 ATP. Also, 10 coenzymes are reduced (8 NADH, 2 FADH2). The coenzymes carry hydrogen ions and electrons to sites of the third stage of aerobic respiration. b The second stage starts after membrane proteins transport pyruvate from the cytoplasm, across both mitochondrial membranes, to the inner compartment. Six carbon atoms enter these reactions (in two pyruvate), and six leave (in six CO2). Many coenzymes form. Fig. 7-5, p.112 Fig. 7-6, p.113 glucose Glycolysis you are here Krebs Cycle Electron Transfer Phosphorylation Fig. 7-6b, p.113 Fig. 7-7, p.114 glucose Glycolysis you are here Krebs Cycle Electron Transfer Phosphorylation Fig. 7-7a, p.114 glucose 2 ATP Glycolysis ATP (2 net) 2 NAD+ 2 NADH 2 pyruvate CYTOPLASM OUTER MITOCHONDRIAL COMPARTMENT 2 NADH 2 CO2 2 NADH 6 NADH 2 FADH2 INNER MITOCHONDRIAL COMPARTMENT 2 acetyl-CoA 4 CO2 Krebs Cycle 2 ATP ADP + Pi Electron Transfer Phosphorylation H+ water H+ H+ H+ 32 ATP H+ oxygen Fig. 7-8, p.115 Fig. 7-9, p.116 Fig. 7-10a, p.117 Fig. 7-11, p.117 FOOD fats fatty acids COMPLEX CARBOHYDRATES glycerol glucose, other simple sugars PROTEINS amino acids acetyl-coA acetyl-coA PGAL Glycolysis NADH pyruvate oxaloacetate or another intermediate of the Krebs Krebs Cycle NADH, FADH2 Electron Transfer Phosphorylation Fig. 7-12a, p.119 sunlight energy in Photosynthesis Driven by energy input from the sun, electrons and hydrogen are used to form ATP. ATP energy drives the synthesis of glucose from hydrogen, electrons (delivered by coenzymes), and carbon dioxide’s atoms. glucose (stored chemical energy) carbon dioxide, water Aerobic Respiration Energy input from two ATP initiates three stages of reactions. Many ATP form during thecomplete breakdown of glucose to carbon dioxide and water. chemical energy in many ATP available to drive nearly all cellular tasks oxygen energy out (heat) energy out (heat) Fig. 7-13, p.120 1 glucose ATP (net) Glycolysis pyruvate NADH Krebs Cycle ATP CO2 FADH2 Electron Transfer Phosphorylation ATP p.122