Question

The next day after gorging yourself on Thanksgiving, it’s time to go for a run to work off some of those calories.

Diagram and explain all the steps of tripalmitoyl glycerol oxidation to CO2 and water. Estimate the number of ATP that will be formed during that process, if all the reactions were occurring in skeletal muscle. Compare that to what you would expect in smooth muscle. Explain.

Answer 1

Answer

• Each cycle of beta oxidation includes four FOUR reactions.

  1. Dehydrogenation of alpha and beta carbons by enzyme acyl CoA dehydrogenase

  2. Hydration to saturate the double bonds and form beta hydroxy acyl CoA by enoyl CoA hydratase

  3. Dehydrogenation of beta hydroxy acylCoA on the beta carbon forming beta keto acylCoA catalysed by beta hydroxy acylCoA dehydrogenase in presence of NAD.

  4. Finally, beta keto acylCoA is split at the beta position by thiolase with the addition of one molecule of CoA. The end products of this reaction are acetyl CoA (C₂ units) and an acyl CoA containing 2 carbon less than the original acyl CoA molecule which undergoes further oxidation by beta oxidation.

  In this way, a long chain fatty acid is degraded completely to acetyl CoA which is completely oxidised to CO₂ and water via the citric acid cycle within mitochondria.

  So 16 carbon palmitic acid undergoes 7 times beta oxidation and produces 8 molecules of acetyl CoA. Each time beta oxidation produces 5 ATP.

  Therefore, total number of ATP formed through beta oxidation are 7*5=35

  Total number of ATP formed on oxidation of acetyl CoA through citric acid cycle are 8*12=96

  Total = 131

  Palmitoyl CoA + 23O₂ + 131P_i + 131ADP ----------> CoA + 131ATP + 16CO₂ + 146 H_2O

  AS it is tripalmitoyl glycerol 3 palmitates * 131 ATP/palmitate = 393 ATP