Question

1. Tristearin, a triacylglycerol (TAG), is a obtained from the complete oxidation 1 molecule of tristearin? Considering the energy of hydrolysis of ATP under physiological conditions, present your answer in kJ/mol (recall that INADH 2.5ATP, 1FADH,= 1.5ATP, 1GTP = 1ATP). Also, be sure to include glycerol oxidation via glycolysis in your calculation, and remember that acyl-CoA synthetase requires I ATP to form 1 FA-CoA from 1 free FA. common component of beef fat. How much energy is

Answer 1

Tristearin is a triacyl glyceride wherein glycerol is linked to 3 stearic acid molecules by ester linkages.

Glycerol metabolism: 1 ATP is required for conversion of glycerol to glycerol phosphate. Glycerol phosphate converts to dihydroxyacetone phosphate, forming 1 NADH. Oxidation of dihydroxyacetone phosphate to CO2 occurs via glycolysis and the TCA cycle. There is formation of 2 ATP and 1 NADH2 via glycolysis. Pyruvate to acetyl CoA will give 1 NADH2. TCA cycle will give 3 NADH2, 1 ATP and 1 FADH2.

Total is 6 NADH2, 3 ATP and 1 FADH2

ATP production from glycerol= (6 X 2.5) + 3 + 1.5= 19.5

However,1 ATP is used in conversion of glycerol to glycerol phosphate

Net ATP production = 18.5 ATP

Stearic acid Beta oxidation: Stearic acid is a saturated fatty acid with 18 carbon atoms. Beta oxidation of stearic acid will produce 8 NADH2, 8 FADH2, when converted to 9 acetyl CoA. Each acetyl CoA undergoes TCA cycle to produce 3 NADH2, 1 FADH2 and 1 ATP (GTP). Hence, TCA cycle will give 27 NADH2, 9 FADH2 and 9 ATP.

Net production = (8+27 NADH2), + (8+9 FADH2) + 9 ATP= 35 NADH2+17FADH2+ 9 ATP

Two ATP is used to convert stearic acid to stearyl CoA and transport it to mitochondria.

Net ATP= (35 X 2.5) + (17 X 1.5) + 9= 87.5 + 25.5 + 9-2= 122-2= 120 ATP

There are three stearic acid molecules in tristearin.

Net ATP from 2 stearic acid molecules= 120*3= 360 ATP

Tristearin ATP= 360+ 18.5= 378.5 ATP

ATP hydrolysis releases 30.5 KJ/mol per ATP

Hence, ATP yield= 378.5 X 30.5 KJ/mol= 11544.25 KJ/mol