How to Calculate the Number of ATP Produced During Beta Oxidation of Fatty Acids?
Beta oxidation of fatty acids takes place in the mitochondrial matrix. And there are three stages of beta-oxidation:
a) In the first step, the fatty acid undergoes oxidative removal of successive 2C units in the form of acetyl-CoA, starting from the carboxyl end of the fatty acyl chain. For example, palmitic acid (16C) undergoes 7 passes through the oxidation sequence. At the end of the cycle, the last two carbons C15 and C16 remain as acetyl-CoA. It is important to note that in the first step, 2 ATPs are utilized for the activation of fatty acids. Besides, NADH and FADH2 are formed in this stage.
b) In the second stage of fatty acid oxidation, the acetyl groups of acetyl-CoA are oxidized to CO2 in the Citric Acid Cycle, which also takes place in the mitochondria.
c) The reduced power (NADH, FADH2) produced during the first and second stage enter into the ETS cycle.
Now, we will take an example to calculate the number of ATPs in the oxidation of fatty acids.
1. Palmitic acid (16C) in the first step breaks into acetyl-CoA in seven steps, but total acetyl-CoA formed is 8. It means you can draw a formula as n/2 is the no. of acetyl-CoA formed from a fatty acid compound.
So, here in this example, the number of acetyl-CoA formed is 16 / 2 = 8 Acetyl-CoA
2. The number of NADH and FADH2 produced in the first process: In the above example, 7 NADH and 7 FADH2 are produced. It means, (n/2) - 1
So, here in the above example, the number of NADH and FADH2 produced = (n/2)-1 = (16/2) -1
= 8-1 = 7
3. The acetyl CoA formed in the first process by the oxidation of fatty acids would enter into the Krebs cycle. Now, we know, that in each acetyl-CoA in Kreb cycle produces -- 3 NADH, 1 FADH2, and 1 ATP are produced. So, for 8 Acetyl-CoA, the number of NADH produced would be 8 x 3 = 21
and the number of FADH2 produced = 8 x 1 = 8
Once the reduced power enters into the ETS, it produces ATP.
Now, we can calculate the ATP produced considering 1 NADH produces 3 ATP and 1 FADH2 produces 2 ATP.
Total number of NADH produced during the first process = 7 NADH = 7 x 3 =21 ATP
Total number of FADH2 produced during the first process = 7FAtDH2 = 7 x 2 = 14 ATP
Total number of NADH2 produced during the Krebs cycle = : 24 = 24 x 3 = 72 ATP
Total numbe of FADH2 produced during the Krebs cycle = : 8 = 8 x 2 = 16 ATP
Total number of ATP formed during the Krebs cycle = = 8 x 1 = 8 ATP
Total ATP == 131
Since 2 ATPs have been utilized for the activation of fatty acids, the net ATP produced would be 131-2 = 129 ATP
If you have understood this concept, can you calculate the number of ATPs produced during the oxidation of Stearic acid (18C)
Note: In exams, only even number carbon compounds are asked because the calculation for odd number of carbon containing fatty acids is complex and varies from one acid to another.
a) In the first step, the fatty acid undergoes oxidative removal of successive 2C units in the form of acetyl-CoA, starting from the carboxyl end of the fatty acyl chain. For example, palmitic acid (16C) undergoes 7 passes through the oxidation sequence. At the end of the cycle, the last two carbons C15 and C16 remain as acetyl-CoA. It is important to note that in the first step, 2 ATPs are utilized for the activation of fatty acids. Besides, NADH and FADH2 are formed in this stage.
b) In the second stage of fatty acid oxidation, the acetyl groups of acetyl-CoA are oxidized to CO2 in the Citric Acid Cycle, which also takes place in the mitochondria.
c) The reduced power (NADH, FADH2) produced during the first and second stage enter into the ETS cycle.
Now, we will take an example to calculate the number of ATPs in the oxidation of fatty acids.
1. Palmitic acid (16C) in the first step breaks into acetyl-CoA in seven steps, but total acetyl-CoA formed is 8. It means you can draw a formula as n/2 is the no. of acetyl-CoA formed from a fatty acid compound.
So, here in this example, the number of acetyl-CoA formed is 16 / 2 = 8 Acetyl-CoA
2. The number of NADH and FADH2 produced in the first process: In the above example, 7 NADH and 7 FADH2 are produced. It means, (n/2) - 1
So, here in the above example, the number of NADH and FADH2 produced = (n/2)-1 = (16/2) -1
= 8-1 = 7
3. The acetyl CoA formed in the first process by the oxidation of fatty acids would enter into the Krebs cycle. Now, we know, that in each acetyl-CoA in Kreb cycle produces -- 3 NADH, 1 FADH2, and 1 ATP are produced. So, for 8 Acetyl-CoA, the number of NADH produced would be 8 x 3 = 21
and the number of FADH2 produced = 8 x 1 = 8
Once the reduced power enters into the ETS, it produces ATP.
Now, we can calculate the ATP produced considering 1 NADH produces 3 ATP and 1 FADH2 produces 2 ATP.
Total number of NADH produced during the first process = 7 NADH = 7 x 3 =21 ATP
Total number of FADH2 produced during the first process = 7FAtDH2 = 7 x 2 = 14 ATP
Total number of NADH2 produced during the Krebs cycle = : 24 = 24 x 3 = 72 ATP
Total numbe of FADH2 produced during the Krebs cycle = : 8 = 8 x 2 = 16 ATP
Total number of ATP formed during the Krebs cycle = = 8 x 1 = 8 ATP
Total ATP == 131
Since 2 ATPs have been utilized for the activation of fatty acids, the net ATP produced would be 131-2 = 129 ATP
If you have understood this concept, can you calculate the number of ATPs produced during the oxidation of Stearic acid (18C)
Note: In exams, only even number carbon compounds are asked because the calculation for odd number of carbon containing fatty acids is complex and varies from one acid to another.
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