Glucose Oxidation and ATP Production: Clarifying the Confusion

1. Introduction to Glucose Oxidation

When discussing the complete oxidation of glucose, biochemists often report varied ATP yields due to different biochemical processes and their efficiencies. In eukaryotic cells, the complete oxidation of one glucose molecule typically yields up to 36-38 ATP, depending on the specific biochemical pathway and the textbooks used. Similarly, in prokaryotic cells, the yield can be slightly higher, with up to 38 ATP produced. However, the latest textbooks suggest a more accurate ATP yield of 30-32 ATP per glucose molecule.

Let's break down the process and calculate the ATP production for 4 glucose molecules.

2. The Complete Oxidation of Glucose

The complete oxidation of glucose involves multiple stages, including glycolysis, the Krebs cycle (or citric acid cycle), and oxidative phosphorylation. These processes convert glucose into pyruvate, which is then further oxidized to generate ATP, NADH, and FADH2.

2.1. Glycolysis

During glycolysis, one glucose molecule is split into two three-carbon pyruvate molecules. This process yields 2 ATP per glucose molecule through substrate-level phosphorylation.

2.2. Citric Acid Cycle (Krebs Cycle)

Each pyruvate molecule is converted into an acetyl-CoA, which enters the Krebs cycle. The Krebs cycle generates 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA molecule. Since there are two acetyl-CoA molecules from one glucose molecule, the total yield from the Krebs cycle is 2 ATP (or GTP), 6 NADH, and 2 FADH2.

2.3. Oxidative Phosphorylation

NADH and FADH2 are further oxidized in the electron transport chain (ETC) to generate ATP. According to the latest textbooks, the ratios of ATP production from NADH and FADH2 are 2.5 and 1.5 ATP per NADH and FADH2 molecule, respectively. Therefore, from 6 NADH and 2 FADH2, the theoretical maximum ATP yield is:

6 × 2.5 2 × 1.5 15 3 18 ATP

Adding the ATP from glycolysis and the Krebs cycle, the total ATP production is:

2 (glycolysis) 18 (ETC) 2 (Krebs cycle) 22 ATP

Thus, the total ATP production for one glucose molecule is: 22 ATP (directly from the Krebs cycle and ETC) 2 ATP (from glycolysis) 24 ATP. When corrected for the updated values, the yield is 30 ATP per glucose molecule.

3. ATP Production from 4 Glucose Molecules

For 4 glucose molecules, the ATP production can be calculated as follows:

4 glucose molecules × 30 ATP per glucose molecule 120 ATP

Therefore, the complete oxidation of 4 glucose molecules will yield 120 ATP in eukaryotic cells.

3.1. Prokaryotic Cells

In prokaryotic cells, the yields are slightly higher, with a theoretical maximum of 38 ATP per glucose molecule. Using the updated values, the yield is 32 ATP per glucose molecule. For 4 glucose molecules, the ATP production is:

4 glucose molecules × 32 ATP per glucose molecule 128 ATP

4. Addressing Obsolete Values

It's important to note that many sources still use the obsolete values of NADH3 and FADH22 ATP. However, these values are outdated and lead to inaccurate calculations of ATP yield. In modern textbooks, such as those by Nelson/Cox or Jeremy Berg, the more accurate values of NADH2.5 and FADH21.5 ATP are used.

4.1. Calculations with Obsolete Values

Using the obsolete values, the theoretical ATP yield from NADH and FADH2 is:

6 × 3 2 × 2 18 4 22 ATP (ETC)

Add the ATP from glycolysis and the Krebs cycle:

22 (ETC) 2 (glycolysis) 2 (Krebs cycle) 26 ATP

Thus, the total ATP production for one glucose molecule using the obsolete values is: 26 ATP.

4.2. ATP Production from 4 Glucose Molecules with Obsolete Values

For 4 glucose molecules, the ATP production is:

4 glucose molecules × 26 ATP per glucose molecule 104 ATP

With these calculations, the complete oxidation of 4 glucose molecules will yield 104 ATP using the obsolete values.

5. Summary

In conclusion, the complete oxidation of one glucose molecule in eukaryotic cells yields up to 30 ATP, with a maximum of 33.45 ATP per glucose molecule as reported by recent studies. This translates to 120 ATP for 4 glucose molecules. In prokaryotic cells, the yield is slightly higher, with a maximum of 32 ATP per glucose molecule, yielding 128 ATP for 4 glucose molecules. It's crucial to use updated values to ensure accurate calculations in biochemistry and cell biology studies.

References

1.

2. Nelson, D. L., Cox, M. M. (2015). Lehninger principles of biochemistry (6th ed.). W.H. Freeman.

3. Berg, J. M., Tymoczko, J. L., Stryer, L. (2007). Biochemistry (6th ed.). W.H. Freeman.