Calculate the ATP yield for the complete oxidation of the 20-carbon unsaturated fatty acid gadoleic acid (a 20:1-Δ9 fatty acid). (You should consider the β-oxidation steps, processing of acetyl-CoA through the citric acid cycle, and electron transport. Production of one GTP should be considered the equivalent of production of one ATP. Enter your answer to three significant figures.) ATPs are gained for each gadoleic acid oxidized

132.5 ATPs

Explanation:

We are Given, gadoleic acid has 20 carbons with one unsaturation at carbon number 9.

And we know that For a saturated fatty acid, one beta oxidation cycle results in 1 acetyl CoA molecule, 1 NADH + H+ and 1FADH2. this cycle occurs in 4 steps:

1. Fatty acyl CoA to trans-enoyl CoA: This step produces 1 FADH2

2. trans-enoyl CoA to beta-hydroxyacyl CoA: No reducing power or ATP is produced, Only hydrolysis of trans alkene takes place.

3. beta-hydroxyacyl CoA to beta-ketoacylCoA: This step produces 1 NADH+ H+

4. Release of one Acetyl CoA and fatty acyl CoA chain short of two carbon atoms.

Now, the cycle of gadoleic acid runs in same way till three acetyl CoA molecules are lost forming three FADH2 and three NADH + H+.

After loss of 3 acetyl CoA molecules, carbon number 7 (of actual chain) becomes acyl CoA and so, isomerase comes into action which converts cis double bond between carbon number 9 and Carbon number 10 to trans bond between Carbon number 8 and Carbon number 9. This isomerization then undergoes hydrolysis (as in step 2 of beta oxidation cycle) and step 3 and 4 take place as usual.

The above changes result in release in one acetyl CoA molecule and 1 NADH + H+ but FADH2 is not formed (because step 1 did not occur)

Remaining fatty acyl CoA containing 12 carbons undergoes 5 cycles of beta oxidation to form 6 acetyl CoA, 5 FADH2 and 5 NADH +H+.

So, a total of 10 acetyl CoA, 8 FADH2 and 9 NADH +H+ are formed in beta oxidation of gadoleic acid.

Now, each acetyl CoA on entering citric acid cycle forms 3 NADH + H+, 1 FADH2 and 1 GTP ( = 1ATP)

So, total 10 acetyl CoA from citric acid cycle will form 30 NADH + H+, 10 FADH2 and 10 GTP ( = 10 ATP)

Overall, complete oxidation of gadoleic acid will form, 39 NADH + H+, 18 FADH2 and 10 GTP ( = 10 ATP)

On ETC, assuming 1NADH + H+ to form 2.5 ATP and 1 FADH2 to form 1.5 ATP,

total ATPs formed will be 97.5 ATP (39 NADH + H+), 27 ATP (18 FADH2) and 10 ATP (10 GTP) = 134.5 ATPs

On the beginning of first cycle of beta oxidation, 2 ATPs are used for activation of fatty acid molecule. (these have to be subtracted)

So, net ATP yield = 134.5 - 2 = 132.5 ATPs