The following reactions convert glycerol to dihydroxyacetone

The following reactions convert glycerol to dihydroxyacetone phosphate. Given these reactions, how many molecules of ATP (or equivalent) would be produced by the complete aerobic catabolism of one molecule of glycerol to CO₂ and H₂O? (Assume that re-oxidation of NADH via the electron transport chain yields the equivalent of 3 ATP, and that re-oxidation of FADH₂ yields 2 ATP.)

glycerol + P_i ---------> glycerol-3-phosphate

glycerol-3-phosphate + NAD⁺ -------> NADH + H⁺ + dihydroxyacetone phosphate

a.23

b.17

c.20

d.25

Solution

glycerol + Pi ---------> glycerol-3-phosphate

glycerol-3-phosphate + NAD+ -------> NADH + H+ + dihydroxyacetone phosphate

a.23-

b.17----------answer

c.20

d.25

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explanation

Total ATP from glycerol

            Conv. To DHAP                     -1 ATP                                                Total:

                                                            +1 NADH (cytoplasmic)        11 ATP

            glycolysis                                +1 NADH(cytoplasmic)         2 NADH (cytoplasmic)

                        (enters halfway)          +2 ATP                                   1 NADH

            Pyruvate met.                          +1 NADH

            Krebs, etc.                               + 10 ATP

                                    11 + (2 x 2.5 if liver, heart, kidney) + (1 x 2.5) = 18.5 ATP

                                    11 + (2 x 1.5 if brain or muscle) + (1 x 2.5 ) = 16.5 ATP

Total ATP from glycerol backbone = 18.5 – 16.5 ATP

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