Question

The oxygen we breathe is consumed during which process during the oxidation of glucose?

Generation of Metabolic Water

Glycolysis

Alcohol Dehydrogenase

Pyruvate Dehydrogenase

Oxidation of NADH to NAD+

Answer 1

Aerobic oxidation of glucose is a multi-step process which includes (a) glycolysis ( conversion of glucose to pyruvate), (b) the tricarboxyllic acid (TCA) cycle, and (c) the electron transport chain (ETC). NAD+ acts as a key electron acceptor molecule in several of the oxidation processes catalyzed by dehydrogenases. In the Glycolysis, for example, Glyceraldehyde 3-phosphate dehydrogenase oxidizes Glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate by reducing NAD+ to NADH. Other dehydogenases including those required in TCA cycle and pyruvate oxidation also need NAD+ as electron acceptor, reducing it to NADH in the process. NADH must replenish itself to NAD+ if the oxidation reactions including that of glucose oxidation are to be continued.

The replenishment  occurs in the mitochondrial electron transport system where NADH reoxidizes itself to NAD+ by donating its electron to the inner mitochindrial membrane enzyme NADH-coenzyme Q oxidoreductase a.k.a Complex 1. This electron is then transferred by a chain of molecules ultimately to molecular O2 ( The last ETC enzyme Complex IV donates its electron to O2 atom). Oxygen, upon recieving electron is thereby reduced to water. Thus, the O2 we breath is utilized for replenishment of NAD+ by oxidation of NADH to NAD+.