Question

how many molecules of ATP are produced in the complete oxidation of a 12-carbon satuated fatty acid?

Answer 1

Fatty acids are broken through beta oxidation into two carbon units and subsequently enter the kreb's cycle at its

start. A 12 carbon fatty acid will produce 6 two carbon units. So in this case n = 6

Also remember each NAD produces 3 ATP and each FADH2 produces 2 ATP (but have in mind that some sources

say 2.5 and 1.5 ATP respectively leading to a lower yield)

Now for each two carbon unit:

Beta oxidation produces 1 NAD and 1 FADH2 which produce (1 x 3) + (1 x 2) = 5 ATP

A turn through the krebs cycle produces directly 1 ATP, plus 3 NAD and 1 FADH2 which subsequently produce (3 x 3) + (1 x 2) = 11 ATP through the electron transport chain. Total 1 + 11 = 12 ATP.

We must also deduct 2 ATP expended for activating the fatty acid molecule at the beginning of the oxidation process.

The formula to use finally is:

(n - 1) x 5 + (n x 12) - 2

and in this case n = 6.

Substitute in values

(6 - 1) x 5 + (6 x 12) - 2 =

25+ 72 - 2 = 95

95 ATP molecules are produced