Notice we kick off our one, two, three carbon molecule, the glyceroaldehyde three phosphate, and the remaining two carbon atoms remain on this activated glyceroaldehyde. Now, in the next step, we have the other substrate molecule basically coming in. So in this particular case, we're going to use ribose phyphosphate. So we have an Aldosubstrate molecule. Remember, we have two substrate molecules and two product molecules that are formed. So this is one of the substrate molecules.