So let's begin in glycolysis. So in glycolysis, we oxidize glucose into pyruvate molecules. In the process, we also generate these NADH molecules. Now, once the NADH molecule is formed in the process of glycolysis, it remains in the cytoplasm. And what happens to it is a special enzyme known as cytoplasmic. Glycerol three phosphate dehydrogenase actually oxidizes the NADH back into NAD plus.