Question

Assuming 2 ATP per NADH and 1 ATP per FADH, how many moles of ATP can be generated in E. coli cell when one mole of arachidonic acid (20:4) is completely oxidized during beta-oxidation? Assume only FADH is produced during beta-oxidation.

a. 93 ATP/mole 20:4

b. 94 ATP/mole 20:4

c. 95 ATP/mole 20:4

d. 96 ATP/mole 20:4

e. 97 ATP/mole 20:4

f. 98 ATP/mole 20:4

Answer 1

Arachidonic acid (20:4) is a 20 carbon chain molecule. 20:4 means 20 Carbon atoms and 4 C=C double bonds.

To completely oxidized a single Arachidonic acid, it undergoes 9 cycles of beta oxidation and generates 10 acetyl CoA.

Here, we have to assume number of ATP generated only by complete beta oxidation of Arachidonic acid.

One FADH2 and one NADH is generated in one cycle of Arachidonic acid beta oxidation. Here, we have to consider only FADH2. So, 9 FADH2 would be generated due to complete beta oxidation of Arachidonic acid.  

Here we have to assume only FADH2 is produced in beta oxidation. Number of ATP from complete beta oxidation of Arachidonic acid  = 1 FADH2 x 9 cycle = 9 ATP (we have to assume 1FADH2 = 1ATP here)

Number of ATP from one Acetyl CoA in Citric Acid Cycle =

(Remember we have to assume 1FADH2 = 1ATP here)

1 FADH2 = 1 ATP

3 NADH = 6 ATP

1 ATP

Total ATP = 10 ATP

Since there are 10 cycles of TCA cycle due to complete oxidation of one mole of Arachidonic acid (20:4), the number ATP generated =

1 ATP (FADH2) x 10 + 6 ATP (NADH) x 10 + 1 ATP (GTP) x 10 = 80 ATP

Total ATP from complete beta oxidation of Arachidonic acid (20:4) = 80 + 9 = 89 ATP

ATP used for activation of Fatty Acid = 2 ATP

Net ATP = 89 - 2 = 87 ATP

Since, this calculation is correct, none of these option seems to be correct.