In the skeletal muscle cells of vertebrate, as many as 36 molecules of ATP are produced from one molecule of glucose. This is less than might be expected, because electrons from NADH produced during glycolysis must be shuttled through the inner mitochondria membrane at a cost. Glucose is first broken down by the process of glycolysis where it is broken down into two 3 carbon pyruvate, which is a substrate for the link reaction. The process uses 2ATP, and produces 4 ATP, making it a net gain of 2ATP. Krebs cycle yields 2 ATP molecules and also NADH and FADH, which joins the electron transport chain. The transport chain in turn yields 32 ATP molecules. The total ATP molecules will therefore be 36 ATP molecules.