Acetyl CoA (2 carbon compound) from the link reaction combines with a 4 carbon compound called oxaloacetate. This reaction releases the CoA enzyme allowing it to be re-used. The now 6 carbon compound (citric acid) releases Co2 to leaving a 5 carbon compound. This reaction also produces NADH, from the coenzyme NAD+ The 5 carbon compound then converts back into the 4 carbon by releasing Co2 , 2 NADH, 2FADH2 and ATP, from ADP and PI.. The cycle can then be repeated. For each molecule of glucose the cycle occurs twice as two acetyl CoA are produced.