Overall Glycolytic Conversions

In anaerobic glycolysis, by definition, no oxygen is present and the tricarboxylic acid cycle cannot proceed, and only lactic acid or lactate is the end product. In aerobic glycolysis, both the tricarboxylic acid cycle and lactic acid or lactate formation can occur. In the preferred limit, only the tricarboxylic acid cycle is assumed to occur. 

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Thus, reversal of the glycolytic step from PEP to pyruvate requires two reactions in gluconeogenesis, pyruvate to oxaloacetate by pyruvate carboxylase and oxaloacetate to PEP by PEP carboxykinase. Given that the conversion of PEP to pyruvate in glycolysis synthesizes ATP, it is not surprising that the overall reversal of this step needs the input of a substantial amount of energy, one ATP for the pyruvate carboxylase step and one GTP for the PEP carboxy kinase step. 

The overall conversion, then, is the conversion of two pentoses into a tetrose (4-carbon) molecule and a hexose. Fmctose-6-phosphate, the hexose, is a glycolytic intermediate and can enter that pathway at this stage. As shown in Figure 12-3, the 4-carbon sugar, erythrose-4-phosphate, reacts with a molecule of xylulose-5-phosphate, catalyzed by transketolase (2-carbon transfer) ... 

Trace glycerol metabolism after it enters the glycolytic pathway as dihydroxyacetone phosphate and give an overall net reaction (including ATP, NAD, etc.) for the conversion of glycerol to... 

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