Question

How many ATP molecules can be generated from one arachidic acid (20:0) molecule? (Draw the arachidic acid structure and show how you calculate your answer)

Answer 1

Arachidic acids are 20 Carbon long fatty acid chain and (20:0) suggest that no double bond is there in the chain.

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

First we need to activate the fatty acid by adding coA with the expense of 2 ATP.

oxidation of fatty acid involves production of acetyl coA. It need 4 basic steps which is considered as 1 cycle, which produce 1 acetyl coA.

1 cycle of beta-oxidation will produce 1 acetyl coA, 1FADH2 and 1 NADH molecules.

We need 9 such cycle to complete oxidation of arachidic acid (20:0). Number of cycles can be calculated as :

i.e. 20/2 -1

i.e. 10-1

i.e. 9.

# now, 9 such cycle will produce 10 acetyl coA, 9 FADH2 and 9 NADH. (2 acetyl coA is released in the last step)

1 acetyl coA will produce 1 ATP, 3 NADH and 1 FADH2 from TCA cycle.

so, 10 acetyl coA will produce 1ATP, 30 NADH and 10 FADH2 from TCA cycle.

# now for complete oxidation of arachidic acid (20:0) we get,

9 NADH + 30 NADH + 9 FADH2 + 10 FADH2 + 10 ATP

i.e. 39 NADH + 19 FADH2 + 10 ATP

i.e. 97.5 ATP + 28.5 ATP +10 ATP ( 1 NADH = 2.5 ATP and 1 FADH2 = 1.5 ATP)

i.e. 136 ATP

Therefore, for complete oxidation of arachidic acid (20:0) we will get 136 ATP.

But, net production of ATP is 134 ATP. Since 2 ATP is used up during activation of fatty acid.