Question

How many ATP is equal to NADH?

Answer 1

Hint: 3 molecules of ATP generated by one molecule NADH in prokaryotes. In case of eukaryotes, 2 - 3 ATP molecules are generated per NADH molecule, for each electron pair is transferred to the electron transport chain.

Complete answer:
The theoretical maximum yield of ATP for the oxidation of one molecule of glucose during aerobic respiration is 38.
Determining the exact yield of ATP for aerobic respiration is difficult for a number of reasons. The number of ATP generated per NADH is not always a whole number. In eukaryotic cells, unlike prokaryotes, NADH generated in the cytoplasm during glycolysis must be transported across the mitochondrial membrane before it can transfer electrons to the electron transport chain which requires energy. As a result, 1-2 ATP are generated from these NADH.
However, considering the theoretical maximum yield of ATP per glucose molecule oxidized by aerobic respiration, for each pair of electrons transferred to the electron transport chain by one molecule of NADH, 3 ATP will be generated.
Total theoretical maximum number of ATP generated per Glucose in Prokaryotes = 38 ATP: 4 from substrate-level phosphorylation + 34 from oxidative phosphorylation.
The ATP yield by NADH is as follows –
Glycolysis : 2 NADH yields 6 ATP by oxidative phosphorylation
Transition Reaction : 2 NADH yields 6 ATP
Citric acid cycle : 6 NADH yields 18 ATP by oxidative phosphorylation
In eukaryotic cells, the theoretical maximum yield of ATP generated per glucose is 36 to 38, depending on how the 2 NADH generated in the cytoplasm during glycolysis enter the mitochondria and whether the resulting yield is 2 or 3 ATP per NADH.
Thus, from the above information, we can conclude two things:
In cytoplasm, one molecule of NADH is equivalent to 2 ATP.
Inside the mitochondria, one molecule of NADH is equivalent to 3 ATP.

Note:
NADH generated in the cytoplasm during glycolysis must be transported across the mitochondrial membrane before it can transfer electrons to the electron transport chain and this requires energy. As a result, between 1 and 2 ATP are generated from these NADH. Also ATP generated in eukaryotes & prokaryotes can be different.