For anyone confused by Rubens whiteboard calculations please see Rubens response below. Hi everyone, Thank you for being such astute viewers! You are spot on that the complete stoichiometry for the average human triglyceride molecule is 10kg [ C55H104O6 ] + 29kg [ O2 ] ---> 28kg [ CO2 ] + 11kg [ O2 ] . We didnt go deeply into this explanation due to time constraints but if you are able to freeze the story at around 6 min 3 sec, those numbers are all there on the white board... with an interesting twist. The 10kg of fat is written in black above the C55H104O6 on the left and the 29kg of inhaled oxygen appears in red above the O2. The total mass of the products on the right must add up to 39kg, as you correctly point out. The two arrows originating from the 10kg of fat on the left arching up and over to the right represent the mass originally contained in the fat of which 8.4kg departs as CO2 and 1.6kg becomes H2O. The remaining mass of the products, which is all derived from the inhaled oxygen, appears below the products on the right and are 19.6kg for CO2 and 9.4kg for H2O. To calculate those 8.4kg and 1.6kg contributions, you need to know precisely what happens to the six oxygen atoms in a C55H104O6 molecule. Do they all depart as CO2 or as H2O or in some combination of the two? The solution is not immediately obvious and it took me months to find the answer which is that 4 out of the 6 atoms become CO2 and the remaining 2 become H2O. You can deduce this from a 1949 paper by Lifson et. al. in the Journal of Biological Chemistry titled The fate of utilized molecular oxygen and the source of the oxygen of respiratory carbon dioxide, studied with the aid of heavy oxygen. The paper is freely available online as a PDF and it’s a fascinating read if you have time. Their experiments showed that A) the heavy oxygen atoms of the labelled water injected into mice turned up in the exhaled CO2 and B) that inhaled heavy oxygen atoms appeared in the body water. This led the authors to conclude that the oxygen of respiratory carbon dioxide would approach equilibrium with body water and that utilized respiratory oxygen would soon find its way into body water.” This is obviously all a bit technical and tricky to fit into a six minute story but I hope that clears up any confusion. Thank you again though, for keeping such a close eye on our program. Best regards, Ruben
Posted on: Fri, 29 Aug 2014 06:52:15 +0000
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