生物化学chap8TCAHMP课件幻灯片.pptVIP

TCA …… Tricarboxylic acid cycle Citric acid cycle Definition 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 process Step 1: pyruvate is converted to acetyl CoA by the enzyme pyruvate dehydrogenase Pyruvate dehydrogenase is a complex of three enzymes; One NAD+ is reduced to NADH Step 2: TCA The 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A 1.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 FADH2 The 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 2CO2 3NAD 3NADH+H＋ GDP GTP FAD FADH2 Section 2 Energy yield Each 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 NADH Glycolysis: 2ATP, 2NADH TCA: 6NADH, 2FADH2, 2GTP(ATP) Total: 10×3+2×2+4=38ATP 10×2.5+2×1.5+4=32ATP EMP :8 Pyruvate to acetylCoA:6 TCA cycle:24 葡萄糖＋6O2＋38ADP＋38Pi 6CO2＋6H2O+38ATP Physiological 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 biosynthe