Glucose vs Hexanoic Acid ATP Yield
This analysis compares the net ATP generated from the complete biological oxidation of glucose and hexanoic acid, both molecules possessing six carbon atoms.
Glucose Oxidation Pathway and ATP
Glucose catabolism involves several stages:
- Glycolysis: Occurs in the cytoplasm, breaking glucose (6C) into two pyruvate molecules (3C each). Net yield: 2 ATP + 2 NADH.
- Pyruvate Oxidation: Pyruvate enters the mitochondria and is converted to Acetyl-CoA (2C). Yields 2 NADH per glucose molecule.
- Krebs Cycle: Acetyl-CoA enters the cycle. For each glucose molecule (2 Acetyl-CoA), the cycle turns twice. Yields: 2 ATP (GTP) + 6 NADH + 2 FADH2 per glucose molecule.
- Oxidative Phosphorylation: Electrons from NADH and FADH2 are used to generate ATP.
Total estimated net ATP from glucose is approximately 30-32 ATP.
Hexanoic Acid Oxidation Pathway and ATP
Hexanoic acid is a 6-carbon saturated fatty acid. Its complete oxidation primarily involves beta-oxidation within the mitochondria:
- Acetyl-CoA Production: A 6-carbon fatty acid yields $6 / 2 = 3$ molecules of Acetyl-CoA.
- Beta-oxidation Cycles: This requires $6 / 2 - 1 = 2$ cycles.
- Energy Yield per Cycle: Each beta-oxidation cycle produces 1 NADH and 1 FADH2. Thus, 2 cycles yield 2 NADH and 2 FADH2.
- ATP Generation: ATP is generated from the 3 Acetyl-CoA molecules entering the Krebs cycle and from the 2 NADH and 2 FADH2 produced during beta-oxidation.
The total estimated net ATP from hexanoic acid (excluding the initial activation cost of approximately 2 ATP) is approximately 38-40 ATP.
Comparative ATP Calculation
A summary of the approximate ATP yields:
| Molecule | Carbon Atoms | Approx. Net ATP Yield |
|---|---|---|
| Glucose | 6 | 30-32 ATP |
| Hexanoic Acid | 6 | 38-40 ATP |
Final ATP Generation Comparison
Fatty acids are more energy-dense than carbohydrates. For molecules of the same length (6 carbons here), the fatty acid (hexanoic acid) yields more ATP than the carbohydrate (glucose). This is because the beta-oxidation pathway is highly efficient at generating Acetyl-CoA and reducing equivalents (NADH, FADH2) relative to the number of carbons compared to glycolysis followed by pyruvate oxidation.
Consequently, hexanoic acid produces more ATP than glucose.
Important Questions from Bioenergetics ATP Hydrolysis
- Assuming that there are $5 \times 10^{13}$ cells in the human body, and that ATP is turning over at a rate of $10^9$ ATP molecules per minute in each cell, then the human body is utilizing ________ watts (rounded off to two decimal places).
[Assume that hydrolysis of ATP yields 12 kcal per mole. 1 watt = 1 joule/sec, 1 calorie = 4.18 joules, Avogadro's number = $6.023 \times 10^{23}$] - Four groups of metabolites are given below. Choose the group in which all the compounds contain at least one bond whose ${\Delta}G'^{\circ}$ of hydrolysis is $\leq$ -7.0 kcal/mole.
- Which one of the following statements is NOT correct?
- Which of the following is TRUE about Kreb's cycle?
- The movement of protons through the $F_0F_1$-ATPase during mitochondrial respiration is required for ________
