In: Chemistry
How many molecules of acetyl-CoA, FADH2 and NADH, and their corresponding electrons are produced from the beta-oxidation of docosanoic acid? From the acetyl CoA produced, how many molecules of FADH2 and NADH are produced? Overall, approximately how many molecules of ATP will docosanoic acid ultimately produce?
Answer.
The formula for docosanoic acid is C22H44O2.
The oxidation of fatty acids is divided into three stages.
In the first stage i.e. beta-oxidation, there is successive removal of two carbon units from the fatty acid to form acetyl-CoA. At the end of 10 cycles, the remaining two carbons of docosanoic acid are left as acetyl-CoA. Thus docosanoic acid will form 11 molecules of acetyl-CoA after going through the cycle 10 times. In each cycle of beta-oxidation, there is production of one molecule of acetyl-CoA and one molecule each of FADH2 and NADH.
So the whole reaction for the first stage can be written as follows:
Docosanoic acid + 10CoA + 10FAD + 10NAD+ + 10H2O 11 acetyl-CoA + 10FADH2 + 10NADH + 10H+
Hence, 11 molecules of acetyl-CoA, 10 molecules of NADH and 10 molecules of FADH2 are produced from the beta-oxidation of docosanoic acid.
The second stage comprises the oxidation of acetyl-CoA formed to CO2. It occurs through the citric acid cycle. The oxidation of one molecule of acetyl-CoA through citric acid cycle produces 3 molecules of NADH, 1 molecule of FADH2 and 1 molecule of GTP.
So the whole reaction of oxidation of 11 molecules of acetyl-CoA will produce 33 molecules of NADH, 11 molecules of FADH2 and 11 molecules of GTP.
The third stage is the conversion of energy producing units such as NADH, FADH2 and GTP into ATP.
According to new concept,
1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP
1 GTP = 1 ATP
Total ATP produced from beta-oxidation,
= (2.5 x 10 NADH) + (1.5 x 10 FADH2)
= 40 ATP.
Total ATP produced from acetyl-CoA oxidation,
= (2.5 x 33 NADH) + (1.5 x 11 FADH2) + (1 x 11 GTP)
= 110 ATP.
So, total ATP produced from docosanoic acid are
= (110 + 40) ATP
= 150 ATP
[ NOTE - According to the old concept, 1 NADH = 3 ATP, 1 FADH2 = 2 ATP, 1 GTP = 1 ATP. So the total ATP produced from docosanoic acid (according to old concept) will be 182 ATP. ]