Question

SHOW ALL WORK PLEASE! Compare the amounts of ATP (per carbon) generated from β-oxidation of stearic acid (18:0) to the amount of ATP generated from glucose during cellular respiration.

Answer 1

Answer-

1. Beta oxidation of stearic acid (18:0) energetics- stearic acid is 18 carbon containing saturated fatty acid so that it cannot be directly pass through mitochondrial membrane. Activated Stearic acid (steryl-CoA) is transported into mitochondria by carnitine shuttle. Activation of fatty acid requires 1ATP. when steryl CoA is transported into matrix it is catabolized by beta oxidation. In each round beta oxidation, 2 carbons in the form of acetyl-CoA is removed and for complete oxidation of 18 carbons 8 rounds of beta oxidation occurs to produce 9 acetyl-CoA. These acetyl CoA enters into Krebs cycle for complete oxidation and to produce ATP

In one round of beta oxidation, 1FADH2 and NADH+H+ is produced and 8 rounds of beta oxidation produces 8FADH2 and 8NADH+H​​​​​​​+ are produced. When 1 acetyl-CoA enters in Krebs cycle 3NADH+H​​​​​​​+ , 1FADH2 and 1GTP are produced. When 9 acetyl-CoA enters Krebs cycle totally 27NADH+H+, 9FADH2 and 9GTP are synthesized.

In beta oxidation of stearic acid (8FADH2 ×1.5=12 ATP) + (8NADH+H+×2.5=20ATP) = 32ATP are produced. Krebs cycle produces (27NADH+H +×2.5= 67.5ATP) + ( 9FADH2 ×1.5 = 13.5ATP) + (9GTP=9ATP) = 90 ATP.

TOTAL AMOUNT OF ATP GENERATED BY BETA OXIDATION OF STEARIC ACID = 32ATP + 90ATP= 122ATP. 1ATP is utilized for activation of stearic acid is subtracted = 122ATP-1ATP= 121ATP.

Stearic acid generates 121 ATP by beta oxidation.

2. Complete oxidation of glucose by respiration-

Glucose is utilized by glycolysis and 2 molecules of pyruvate are produced. In glycolysis 2NADH+H​​​​​​​+ and 4ATP are produced and 2ATP are utilized. So totally (2NADH+H+×2.5=5ATP) + 4ATP= 9ATP. In preparatory phase 2ATP are utilized that are subtracted and 9ATP-2ATP=7ATP are produced. 2 Pyruvates are  then converted to 2 acetyl-CoA and 2NADH +H+ are produced. So that this reaction produces (2NADH+H+×2.5=5ATP) 5ATP are produced. For complete oxidation of glucose, acetyl-CoA enters in respiration by moving into Krebs cycle and each acetyl-CoA when moves through Krebs cycle 3 NADH+H​​​​​​​+, 1FADH2 and 1GTP are produced. 2 acetyl-CoA produces 6 NADH+H​​​​​​​+, 2FADH2 and 2GTP are produced. Totally via Krebs cycle (6NADH2×2.5=15ATP)+(2FADH2×1.5=3ATP) + (2GTP=2ATP)= 20ATP.

The complete oxidation of glucose by respiration produces 7ATP (glycolysis) + 5ATP (pyruvate to acetyl CoA) + 20 ATP = 32 ATP are produced.