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1、(五) TCA循环,丙酮酸在进入三羧酸循环之先要脱羧生成乙酰CoA,乙酰CoA和草酰乙酸缩合成柠檬酸再进入三羧酸循环。 循环的结果是乙酰CoA被彻底氧化成CO2和H2O,每氧化1分子的乙酰CoA可产生12分子的ATP,草酰乙酸参与反应而本身并不消耗。,TCA循环的重要特点,1、循环一次的结果是乙酰CoA的乙酰基被氧化为2分子CO2,并重新生成1分子草酰乙酸; 2、整个循环有四步氧化还原反应,其中三步反应中将NAD+还原为NADH+H+,另一步为FAD还原; 3、为糖、脂、蛋白质三大物质转化中心枢纽。 4、循环中的某些中间产物是一些重要物质生物合成的前体; 5、生物体提供能量的主要形式; 6、为
2、人类利用生物发酵生产所需产品提供主要的代谢途径。如 柠檬酸发酵;Glu发酵等。,三羧酸循环的枢纽位置,二、递氢、受氢和ATP的产生,经上述脱氢途径生成的NADH、NADPH、FAD等还原型辅酶通过呼吸链等方式进行递氢,最终与受氢体(氧、无机或有机氧化物)结合,以释放其化学潜能。 根据递氢特别是受氢过程中氢受体性质的不同,把微生物能量代谢分为呼吸作用和发酵作用两大类.,发酵作用:没有任何外援的最终电子受体的生物氧化模; 呼吸作用:有外援的最终电子受体的生物氧化模式; 呼吸作用又可分为两类: 有氧呼吸最终电子受体是分子氧O2; 无氧呼吸最终电子受体是O2以外的 无机氧化物,如NO3-、SO42-等
3、.,FERMENTATION:,Example: On the left side, glucose is oxidized to pyruvate. On the right side, pyruvate can be reduced to acids, alcohols and gases.,RESPIRATION:,ANAEROBIC RESPIRATION employs an electron acceptor other than O2 such as nitrate (NO3) which is reduced to nitrite (NO2) or N2.,PHOTOTROPH
4、Salso oxidize chemical compounds, but the ultimate source of energy is light. Phototrophy is shown here as the set of light-dependant, catabolic reactions associated with photosynthesis (the other reactions of which are anabolic).,PHOTOTROPHY:,(chl represents chlorophyll.) Phototrophy can be OXYGENI
5、C (evolving O2 when H2O serves as the electron donor) or ANOXYGENIC (non-O2-evolving).,Fermentation - oxidation of an organic compound in the absence of external electron acceptor (no oxygen required). Uses SLP (substrate-level phosphorylation) Respiration - oxidation of an organic compound where ox
6、ygen is the final electron acceptor. Uses ETS (electron transport system) as well as SLP Anaerobic respiration (unique to bacteria) - oxidation of organic compounds where an external substrate other than oxygen serves as final electron acceptor. Exs: nitrate, sulfate, carbon dioxide,Mechanisms of energy release: overview,