Glucose Plasma membrane NAD+ Oxygen present Glycolysis NADH Pyruvate NAD Pyruvate NAD Oxygen absent ATP NADH Acetyl CoA ATP Fermentation TCA cycle NAD* ATP NADH e Electron Cytosol Carbon dioxide transport chain and water Lactate Figure 5.5 An overview of carbohydrate metabolism in eukaryotic cells.The reactions of gly- colysis generate pyruvate and NADH in the cytosol.In the absence of O2,the pyruvate is reduced by NADH to lactate(or another product of fermentation,such as ethanol in yeast;see Figure 3.27 for details).The NAD+formed in the reaction is reutilized in the continuation of glycolysis.In the主讲：汤 华