The net energetic production from the metabolism of one mole of galactose to pyruvate is 2 moles of ATP, which is calculated from the process of glycolysis.
To explain further, when galactose enters the glycolytic pathway, it is converted into glucose-6-phosphate and then it undergoes the same series of reactions as glucose. During glycolysis, for every molecule of glucose processed, the net yield is 2 ATP and 2 NADH. However, galactose must first be converted into glucose, which requires the input of energy in the form of ATP during the conversion of galactose to glucose-1-phosphate.
Although there is an initial investment of 1 ATP, the reactions that follow in glycolysis lead to the production of the same 2 ATP and 2 NADH. Accounting for the energy used to convert galactose to glucose, the overall yield becomes:
- 2 ATP produced in glycolysis
- -1 ATP used to convert galactose to glucose
Thus, the net energetic production from the metabolism of one mole of galactose to pyruvate ends up being:
Net Production = 2 ATP (produced) – 1 ATP (used) = 1 ATP
Additionally, 2 NADH are produced during glycolysis which can yield about 5 ATP when oxidized through the electron transport chain. So when considering the yield of NADH, the total energetic production from galactose to pyruvate can be summed up as:
- 1 ATP (net gain from glycolysis)
- 5 ATP (from 2 NADH)
Therefore, the total comes closer to 6 ATP equivalent from one mole of galactose to pyruvate when taking into consideration all energy currencies produced.