Question

2. Arshamia ovidbarbidae uses triglycerides as a major source of energy. During catabolism of triglycerides, this species uses a triglycerides lipase to hydrolyse glycerol from the molecule, releasing the three constituent fatty acids. The R1 and R2 fatty acids (I.e. including the COO terminus) are Lauric acids while R3 is Stearic acids.

Assuming that this species has all the necessary capabilities to run Embden-Meyerhoff glycolysis, Krebs TCA, and anerobic electron transport and oxidative phosphorylation, determine the theoretical maximum ATP production (moles) from the complete oxidation of one mole of this triglyceride. Do not neglect the glycerol molecules released during the initial stages. Include in your answer an explanation of the pathways (and highlight events) that you would expect to occur in this process.

Answer 1

Fatty acid oxidation is called -oxidation because the bond between alpha (C2) and beta(C3) carbon of the fatty acid is broken during each round of cycle. Beta oxidation of fatty acids occurs within the mitochondrial matrix. Beta - oxidation involves the sequential removal of 2-carbon segments in the form of acetyl-CoA and production of shortened acyl-CoA, with concurrent reduction of one FAD and one NAD+.

Glycerol requires 1 ATP per molecule for the conversion into glycerol phosphate. The glycerol phosphate then converted to dihydroxyacetone phosphate with the production of 1 molecule of NADH. The dihydroxyacetone phosphate can be oxidized fully to CO2 through glycolysis and the TCA cycle.

In the conversion to pyruvic acid, dihydroxyacetone phosphate generate:- 1NADH and 2 ATP molecule as per glycerol molecule. The net effect of converting glycerol to pyruvic acid is: -1 ATP + 2 ATP + 2 NADH = 1 ATP + 2 NADH = 6 ATP, assuming that the NADH are both oxidized with the generation of 2.5 ATP per NADH. The complete oxidation of pyruvate produce 4 NADH, 1 FADH2 and 1 GTP. When the reducing equivalents are oxidisef through the electron transport chain, this produce:

4 NADH × 2.5 ATP / NADH + 1 FADH2 × 1.5 ATP/ FADH2 + 1 GTP × 1 ATP/ GTP = 12.5 ATP.

Each glycerol molecules liberated from a triglyceride thus produces at most 18.5 molecules ATP per molecules glycerol.

Glycerol has a gram molecular weight of 92g/mol. It produces 18.5 moles ATP/92g/mol = 0.20mol/g.

This is a little more than the energy derived from glucose: 32 moles ATP/180g/mol = 0.18 /g.