Calculate the number of ATPS generated from the metabolic oxi-dation of the four carbons of acetoacetyl-CoA to CO,. Nowconsider the homolog derived from oxidation of an odd-numberedcarbon chain, namely propionoacetyl-CoA. Calculate the net ATPyield from oxidation of the five carbons of this compound to CO,.

Answered: Calculate the number of ATPS generated…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Question

Calculate the number of ATPS generated from the metabolic oxi-
dation of the four carbons of acetoacetyl-CoA to CO,. Now
consider the homolog derived from oxidation of an odd-numbered
carbon chain, namely propionoacetyl-CoA. Calculate the net ATP
yield from oxidation of the five carbons of this compound to CO,.

Expert Solution

Step 1

The oxidation of fatty acyl-CoA occurs inside the mitochondrial matrix through the sequence of four biochemical reactions involving dehydrogenation, hydration, dehydrogenation, and thiolysis and these reactions are collectively called as $β$ -oxidation. This $β$ -oxidation keeps on operating until the fatty acyl-CoA chain is broken down up to the level of acetyl CoA which enters the Krebs cycle for final oxidation to generate energy.

Step 2

The aceto-acetyl CoA is the four carbon even numbered fatty acyl-CoA. So, aceto-acetyl CoA will undergo 1 cycle of beta oxidation to produce two acetyl-CoA molecules which will enter Krebs cycle to generate energy.

In Beta-Oxidation, 1 molecule of FADH₂ and 1 molecule of NADH is also produced during the course of four sequential reactions which will get completely oxidized in oxidative phosphorylation to yield ATP. The end products are two molecules of acetyl-CoA which will enter Krebs cycle.

Total ATP from $β$ -oxidation of Aceto-acetyl CoA=ATP from NADH+ATP from FADH₂

And, 1 molecule of NADH in oxidative phosphorylation=2.5 ATP

1 molecule of FADH₂ in oxidative phosphorylation=1.5 ATP

$∴$ Total ATP from $β$ -oxidation of Aceto-acetyl CoA=(2.5+1.5) ATP=4 ATP

In Krebs cycle, 1 acetyl-CoA is metabolized to 3 molecules of NADH, 1 molecule of FADH₂, and 1 molecule of ATP.

Total ATP from Krebs cycle of 2 Acetyl CoA= ATP from $3 \times 2 = 6$ NADH+ATP from $1 \times 2 = 2$ FADH₂+ $1 \times 2 = 2$ ATP

1 molecule of NADH in oxidative phosphorylation=2.5 ATP

So, 6 molecules of NADH in oxidative phosphorylation=15 ATP

1 molecule of FADH₂ in oxidative phosphorylation=1.5 ATP

So, 2 molecules of FADH₂ in oxidative phosphorylation=3 ATP

$∴$ Total ATP from Krebs cycle of 2 Acetyl CoA=(15+3+2) ATP=20 ATP

Therefore, total ATP generated from metabolic oxidation of four carbons of aceto-acetyl CoA=Total ATP from $β$ -oxidation of Aceto-acetyl CoA + Total ATP from Krebs cycle of 2 Acetyl CoA = (4+20) ATP= 24 ATP.