Question

Oleate is a C fatty acid with one double bond between the and carbons. The ? oxidation of a saturated fatty acid with an equivalent number of carbons would yield ATP: cycles of ? oxidation = ATP; acetyl-CoA yield ATP via the citric acid cycle and oxidative phosphorylation; and ATP are consumed in activating the fatty acid. During ? oxidation of oleate, the presence of the double bond allows the FADH2-generating acyl-CoA dehydrogenase step to be skipped, at a cost of ATP equivalents. Therefore, the ATP yield from oleate is .

Answer 1

Oleic acid, an 18-carbon monounsaturated fatty acid has one cis double bond. This double bond is present between the C9 and C10 carbons.

Fatty acids enter the cell via fatty acid transporter proteins present on cell surface. A CoA molecule is added to the oleic acid by fatty acid CoA synthase to form oleoyl CoA. This activation consumes 2 ATP molecules, as ATP is converted to AMP. Oleoyl CoA undergoes three cycles of ?-oxidation. This results in formation of 3 molecules of acetyl CoA. A 12-carbon fatty acyl-CoA with a cis double bond beween C3 and C4, known is also formed. As cis-?3-Dodecenoyl-CoA has a cis double bond, no further ?-oxidation of this product occurs. The enzyme ?3,?2-enoyl-CoA isomerase converts cis-?3-Dodecenoyl-CoA to trans-?2-Dodecenoyl-CoA. The trans-?2-Dodecenoyl-CoA can enter beta-oxidation to yield another 6 molecules of acetyl CoA. All 9 (6+3) acetyl-CoA enter the Krebs cycle and later oxidative phosphorylation. From each acetyl CoA, Krebs cycle gives 3 NADH, 1 FADH2 and one ATP (or GTP). Each NADH= 3 ATP while 1 FADH2 = 2 ATP.

Each beta oxidation also produces one NADH and one FADH2 molecules.

In oleic acid breakdown, the FADH2 generating acyl CoA dehydrogenase step is skipped. 2 ATP are consumed in activating the fatty acid. Hence, from oleic acid, 8 NADH, 7 FADH2, and 9 acetyl CoA are produced. 2 ATP are utilized for activation of oleoyl CoA.

8 NADH= 8*3= 24 ATP

7 FADH2= 7*2= 14 ATP

1 Acetyl CoA= 1 FADH2, 3 NADH and 1 ATP

9 Acetyl CoA= 9 FADH2, 27 NADH and 9 ATP

Total ATP yield from 9 acetyl CoA= (9*2) + (27*3) + 9= 18+81+9= 108 ATP

ATP yield from oleic acid= 24 + 14+ 108= 146 ATP

Negating the 2 ATP used for activation,

Total ATP yield from oleic acid breakdown= 146-2=144 ATP

Hence, from 1 oleic acid, 144 ATP are formed