Question

Assuming 1.5 ATP per FADH, 2.5 ATP per NADH in mitochondria, compare approximately how many ATP equivalents would be generated from the complete oxidation of 12-carbon worth of

a. saturated fatty acid

b. sugar (e.g. glucose)

Show work (possibly drawing out the cycle).

Answer 1

12-carbon worth of glucose means 2 glucose molecules.

1 glucose molecule via glycolysis generates 2 pyruvate, 4 ATP, and 2 NADH and consumes 2 ATP.

2 glucose molecules via glycolysis generate 4 pyruvate, 8 ATP, and 4 NADH and consumes 4 ATP.

These pyruvate molecules are converted to acetyl-CoA while generating 1 NADH (4 Pyruvate give 4 acetyl-CoA and 4 NADH).

1 acetyl-CoA via TCA cycle generates 3 NADH, 1 FADH2, and 1 GTP.

4 acetyl-CoA via TCA cycle generates 12 NADH, 4 FADH2, and 4 GTP.

2 Glucose generates 4 pyruvate, 8 ATP, and 4 NADH and consumes 4 ATP.

4 Pyruvate produces 4 NADH while generating acetyl-CoA.

Overall, for 2 glucose,

20 NADH = 50 ATP (20 x 2.5) (1 NADH produces 2.5 ATP)

4 FADH2 = 6 ATP (4 x 1.5) (1 FADH2 produces 1.5 ATP)

4 GTP = 4 ATP

8 ATP = 8 ATP

Total = 68 ATP from oxidation of 2 glucose (12 carbon worth). 4 ATPs are consumed during glycolysis. Subtracting that, the total number of ATPs produced per 2 glucose molecules is 64.

One 12-carbon fatty acid via β-oxidation generates 5 FADH2, 5 NADH, & 6 acetyl-CoA and consumes 1 ATP for its activation.

1 acetyl-CoA via TCA cycle generates 3 NADH, 1 FADH2, and 1 GTP.

6 acetyl-CoA via TCA cycle generates 18 NADH, 6 FADH2, and 6 GTP.

Overall, oxidation of one 12-carbon fatty acid via β-oxidation and TCA cycle generates,

23 NADH = 57.5 ATP (23 x 2.5) (1 NADH produces 2.5 ATP)

11 FADH2 = 16.5 ATP (11 x 1.5) (1 FADH2 produces 1.5 ATP)

6 GTP = 6 ATP

Total = 80 ATP form oxidation of one 12-carbon fatty acid (lauric acid). 1 ATP is consumed for fatty acid activation. Subtracting that, the total number of ATPs produced per 12-carbon fatty acid is 79.

Generation of NADH, FADH2, & GTP is circled in red color, while ATP consumption is circled in black.