During ATP production through the citric acid cycle, some ATP is used to transport necessary molecules for the reactions.
* piruvate molecules are actively transported into the mitochondrial matrix [2]
* two NADH equivalents from glycolisis are transported into the mitochondrion and consume two molar equivalents ATP [1]
* protons leakage across the mitochondrial membrane leads to reduced ATP from NADH and FADH2 [1]
In theory, one molar equivalent of glucose can generate 38 equivalents of ATP. The actual number is only 25 [1].
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**References:**
1. Wikipedia contributors, "Citric acid cycle," Wikipedia, The Free Encyclopedia, (accessed June 26, 2014).
2. Wikipedia contributors, "Mitochondrion," Wikipedia, The Free Encyclopedia, (accessed June 26, 2014).