Question

Describe the complete oxidation of a single 20 carbon fatty acid. Determine the ATP generated from this fatty acid and show your work.

Answer 1

For an even-numbered saturated fat (C2n), n - 1 oxidations are necessary, and the final process yields an additional acetyl CoA. In addition, two equivalents of ATP are lost during the activation of the fatty acid. Therefore, the total ATP yield can be stated as: (n - 1) × 14 + 10 - 2 = total ATP.

The ATP yield for every oxidation cycle is theoretically a maximum yield of 17, as NADH produces 3 ATP, FADH2 produces 2 ATP and a full rotation of the citric acid cycle produces 12 ATP.[citation needed] In practice it is closer to 14 ATP for a full oxidation cycle as the theoretical yield is not attained - it is generally closer to 2.5 ATP per NADH molecule produced, 1.5 ATP for each FADH2 molecule produced and this equates to 10 ATP per cycle of the TCA[citation needed](according to the P/O ratio), broken down as follows:

Source	ATP	Total
1 FADH2	x 1.5 ATP	= 1.5 ATP (Theoretically 2 ATP)[citation needed]
1 NADH	x 2.5 ATP	= 2.5 ATP (Theoretically 3 ATP)[citation needed]
1 acetyl CoA	x 10 ATP	= 10 ATP (Theoretically 12 ATP)[citation needed]
TOTAL		= 14 ATP

For an even-numbered saturated fat (C2n), n - 1 oxidations are necessary, and the final process yields an additional acetyl CoA. In addition, two equivalents of ATP are lost during the activation of the fatty acid. Therefore, the total ATP yield can be stated as:

Formula : (n-1)× 14 + 10-2

For C20  , n=10

Using the formula for even number of carbon :

(10-1)×14+10-2

=126+8 = 134 ATP generated