... molecule with six carbon atoms is eventually split into two molecules of pyruvate, each with three carbon atoms. Energy from ATP is needed in the first steps, but energy is released in later steps, when it can be used to make ATP. There is a net gain of two ATP molecules per molecule of glucose broken down. Glycolysis takes place in the cytoplasm of the cell. In the first stage phosphorylation glucose is phosphorylated using ATP. Glucose is energy rich but does not react easily. To tap the bond energy of glucose, energy must first be used to make the reaction easier. Two ATP molecules are used for each molecule of glucose to make hexose biphosphate, which breaks down to produce two molecules of triose phosphate. Hydrogen is then removed from triose phosphate and transferred to the carrier molecule NAD (nictoinamide adenine dinucleotide). Two molecules of reduced NAD are produced ...

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