Final answer:
The complete catabolism of one molecule of glucose by means of glycolysis and the TCA cycle typically yields a total of 38 ATPs, although this number can vary slightly depending on the organism and specific cellular conditions.
Step-by-step explanation:
The total number of ATPs produced when glucose is completely catabolized by means of glycolysis and the TCA cycle (also known as the Krebs cycle or citric acid cycle) is typically taught as 38 ATPs for higher eukaryotes, such as humans. Here is how that total is calculated:
- Glycolysis yields a net gain of 2 ATPs directly, plus 2 NADH which can be converted into approximately 5 to 6 ATPs when transferred to the electron transport chain (ETC). However, because this transfer may involve a shuttle that uses some ATP, we often count it as 2 ATPs per NADH, for a total of 4 ATPs from NADH.
- Conversion of 2 pyruvate molecules into 2 acetyl-CoA generates 2 NADH, which are equivalent to 6 ATPs (3 ATPs per NADH).
- Two cycles of the citric acid cycle are needed for the complete metabolism of one glucose molecule, and this produces a total of 24 ATPs (since each cycle generates 12 ATP, two cycles double that amount).
Summing these numbers, we get a total of 38 ATPs produced from one molecule of glucose when oxygen is available.
Depending on specific cellular conditions and the organism in question, this number can vary. Some references might cite 36 ATPs as the total yield, as some energy can be lost in the transport of intermediates and ATP yield from NADH in the ETC may vary slightly depending on the shuttle system used in the cell. The overall process includes glycolysis, the conversion of pyruvate to acetyl-CoA, the citric acid cycle, and oxidative phosphorylation, which occurs in the ETC.