The standard starting point for the TCA cycle is acetyl CoA and its condensation with oxaloacetate to form citrate (Reaction 1). As a connection between glycolysis and the TCA cycle, the conversion of pyruvate to acetyl CoA is referred to here as "Reaction 0". Some features of the pyruvate dehydrogenase reaction and images of the cofactors involved can be viewed with a click on that link.