Glucose glyceraldehyde-3-phosphate converting from

E. In the second phase of glycolysis, two glyceraldehyde 3-phosphate molecules from glucose are converted to pyruvate in conjunction with several important energy-generating reactions (Figure 6—1). 

Mode 4. Both NADPH and ATP are required. Alternatively, ribose 5-phosphate formed by the oxidative phase of the pentose phosphate pathway can be converted into pyruvate. Fructose 6-phosphate and glyceraldehyde 3-phosphate derived from ribose 5-phosphate enter the glycolytic pathway rather than reverting to glucose 6-phosphate. In this mode, ATP and NADPH are concomitantly generated, and five of the six carbons of glucose 6-phosphate emerge in pyruvate. 

In glycolysis, dehydrogenation of the two molecules of glyceraldehyde 3-phosphate derived from each molecule of glucose converts two molecules of NAD to two of NADH. Because the reduction of two molecules of pyruvate to two of lactate regenerates two molecules of NAD, there is no net change in NAD or NADH ... 

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