TCA Tricarboxylic acid cycle Citric acid cycleDefinition The cycle oxidizes pyruvate to CO2 and H2O , with the concomitant production of energy (ATP).Location The cycle occurs within the mitochondria（线粒体） of eukaryotes（真核生物） and cytosol（细胞质） of prokaryotes （原核生物）.Section 1 The cycle processStep 1:pyruvate is converted to acetyl CoA by the enzyme pyruvate dehydrogenasel Pyruvate dehydrogenase is a complex of three enzymes;l One NAD+ is reduced to NADHStep 2: TCAThe cycle carries out the oxidation of acetyl groups from acetyl CoA to CO2 with the production of four pairs of electrons, stored initially in the reduced electron carriers NADH and FADH2.TCA草酰乙酸柠檬酸异柠檬酸a-酮戊二酸琥珀酸 辅酶A琥珀酸延胡索酸苹果酸乙酰辅酶A1.柠檬酸合成酶2.顺乌头酸酶3.异柠檬酸脱氢酶4.a-酮戊二酸脱氢酶系5.琥珀酸硫激酶6.琥珀酸脱氢酶7.延胡索酸水合酶8.苹果酸脱氢酶Step 3: Oxidation of NADH and FADH2The NADH and FADH2 produced by the citric acid cycle are reoxidized and the energy released is used to synthesize ATP by oxidative phosphorylation.Acetyl-CoA 2CO23NAD3NADH+HGDPGTPFADFADH2Section 2 Energy yieldEach of the three NADH produced per turn of the cycle yields 3 ATPs and the single FADH2 yields 2 ATPs by oxidative phosphorylation. One GTP (or ATP) is synthesized directly during the conversion of succinyl CoA to succinate. Thus the oxidation of one acetyl CoA via TCA produces 12 ATP. How many ATP molecules are generated with 1 molecule of pyruvate through TCA pathway? How many ATP molecules are generated with 1 molecule of glucose through EMP-TCA pathway?( one glucose is oxidized to CO2 and H2O.)Oxidation of 2 pyr to 2 acetyl CoA: 2 NADHGlycolysis: 2ATP, 2NADHTCA: 6NADH, 2FADH2, 2GTP(ATP)Total: 103+22+4=38ATP 102.5+21.5+4=32ATP EMP :8 Pyruvate to acetylCoA:6 TCA cycle:24葡萄糖6O238ADP38Pi 6CO26H2O+38ATPPhysiological importance of EMP-TCA pathway A common pathway for complete oxidation of carbohydrates into CO2 and H2O. Main source for energy supply To produce intermediates for biosynthetic pathways TCA is the common pathway for complete oxidative catabolism of macromolecules in organism (protein, nucleic acid and lipid) 糖、脂、蛋白质等物质彻底氧化的途径； 生成大量的ATP，是机体利用糖或其它物质氧化获得 能量的最有效方式； 合成代谢提供原料; 糖、脂、蛋白质三大物质转化的枢纽.Physiological importance of EMP-TCA HMP(Hexose monophosphate pathway)(pentose phosphate pathway, PPP)IntroductionReducing power is available in a cell both as NADH and NADPH, but these have quite distinct roles. The core set of reactions of the pathway oxidize glucose 6-phosphate to ribose 5- phosphate and generate NADPH. NADH is oxidized by the respiratory chain to generate ATP via oxidative phosphorylation. NADPH is used for biosynthetic reactions that require reducing power (such as synthesis of fatty acids and steroids)转酮醇酶转酮醇酶转醛醇酶Biochemical process 6-phosphate glucose dehydrogenase6-phosphate gluconic acid dehydrogenase6(glucose-6-P)6O2 5(glucose-6-P)+6CO25H2O62NADP62NADPH+Hglucose ATP ADPHow many ATP molecules are generated with 1 molecule of pyruvate through TCA pathway?Energy yield35 ATPFunctions Another pathway for complete oxidation of carbohydrates; an assistant pathway of EMP (70% by EMP, 30% by HMP) To supply reducing power NADPH for biosynthetic reactions (lipid anabolism) Intermediates of HMP are used materials to synthesize compounds (such as ribose 5- phosphate)(An important pathway for pentose metabolism)gluconeogenesis (anabolism of glucose) Gluconeogenesis (糖的异生作用)the process for nonsugars (e.g. AA, organic acid etc.) to be turned into saccharides in organism.草酰乙酸磷酸烯醇式丙酮酸羧化激酶酯酶酯酶Lactic acidalanineglycerol凡能生成丙酮酸的物质均可转变为葡萄糖；脂肪酸氧化分解产生的乙酰CoA不能逆转为丙酮酸，因 而不能异生为葡萄糖；