 The two pyruvate molecules then move toward the mitochondria in order to enter the citric acid cycle, but they need to be escorted into the cycle. Coenzyme A is a molecule that acts as an escort for these molecules. When CoA attaches to the pyruvate, it removes a carbon that's lost to CO2 waste. The resulting two-carbon molecules linked to CoA are called acetyl-CoA. Acetyl-CoA enters the citric acid cycle where the CoA lets go and the two-carbon molecules link up to a four-carbon molecule called oxaloacetate to form a six-carbon molecule called citrate or citric acid. NAD plus picks up an electron from the citrate and then becomes NADH and heads to the electron transport chain. A carbon molecule is lost by citrate to CO2 and it becomes a five-carbon molecule. Another carbon molecule is lost to CO2 and it becomes a four-carbon molecule. A phosphate group is added to an ADP molecule making ATP. FAD then picks up an electron to become FADH2 and heads to the electron transport chain. NAD plus picks up an electron, becomes NADH, and also heads to the electron transport chain. The four-carbon molecule left in the cycle is oxaloacetate, which can link to another acetyl molecule and the cycle can repeat.