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The Citric Acid Cycle
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Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle. This step is carried out by a multienzyme complex that catalyses three reactions (blue numbers). Figure 9.10 MITOCHONDRION CYTOSOL CO2 Coenzyme A 1 3 2 NAD NADH + H Acetyl CoA Pyruvate What is getting oxidized? Transport protein
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After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules This process happens in the mitochondria of eukaryotic cells only when O2 is present.
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The Citric Acid Cycle The citric acid cycle (also called the Krebs cycle) completes the break down of pyruvate to CO2. The cycle oxidizes organic fuel (acetyl coA). And generates 1 ATP, 3 NADH, and 1 FADH2 per turn. How many of each does it make per glucose molecule?
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Summary Picture (the important stuff!) Pyruvate CO2 NAD CoA NADH + H
Figure 9.11 Pyruvate Summary Picture (the important stuff!) CO2 NAD CoA NADH + H Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD FAD 3 NADH + 3 H ADP + P i ATP
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The citric acid cycle has eight steps, each catalyzed by a specific enzyme.
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Figure Acetyl CoA CoA-SH 1 Oxaloacetate Citrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle. The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate.
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Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle. The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle.
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Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate
Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle.
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Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate
Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle. 4 CO2 NAD NADH Succinyl CoA + H
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Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate
Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 CoA-SH -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle. 4 CoA-SH 5 CO2 NAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP
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Citric acid cycle Acetyl CoA Oxaloacetate Citrate Isocitrate Fumarate
Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle NADH 3 + H CO2 Fumarate CoA-SH -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle. 4 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP
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Citric acid cycle Acetyl CoA Oxaloacetate Malate Citrate Isocitrate
Figure Acetyl CoA CoA-SH 1 H2O Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle NADH 3 7 + H H2O CO2 Fumarate CoA-SH -Ketoglutarate Figure 9.12 A closer look at the citric acid cycle. 4 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP
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Figure Acetyl CoA CoA-SH NADH The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain. + H 1 H2O NAD 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle NADH 3 7 + H H2O CO2 Fumarate CoA-SH -Ketoglutarate 4 Figure 9.12 A closer look at the citric acid cycle. 6 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P i NADH GTP GDP Succinyl CoA + H ADP ATP
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Concept Map Carbon dioxide Oxygen Glucose Water H+ ions
Cellular Respiration Aerobic Anaerobic Glycolysis The Citric Acid Cycle Oxidative Phosphorylation The Electron Transport Chain Fermentation ATP NADH NAD+ Carbon dioxide Oxygen Glucose Water H+ ions Membrane proteins Mitochondria Cytosol Eukaryotes Prokaryotes
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