Question

How many ATP molecules are produced during aerobic respiration of one molecule of glucose?

• A. 24
• B. 3
• C. 2
• D. 38

Answer 1

The correct option is D 38

During aerobic respiration, complete oxidation of one glucose molecule produces 38 ATP molecules. Aerobic respiration involves glycolysis, link reaction (oxidative decarboxylation of pyruvate), Krebs cycle and oxidative phosphorylation.

During glycolysis, there is net gain of 2 molecules of ATP and also 2 molecules of $NADH+H^{+}$ are produced.
Oxidation of 1 molecule of $NADH+H^{+}$ yields 3 molecules of ATP, so, 2 molecules of $NADH+H^{+}$ yield 6 molecules of ATP. Therefore in glycolysis:

Total ATP produced = 2 ATP + 6 ATP (produced by oxidation of $NADH+H^{+}$)
= 8 ATP.

Thus glycolysis yields 8 ATP molecules.

Pyruvate formed during glycolysis in the cytoplasm enters mitochondria and undergoes oxidative decarboxylation to form acetyl CoA. During this reaction, one $NADH+H^{+}$ is produced.
As 2 molecules of pyruvate are formed from one molecule of glucose, 2 molecules of pyruvate undergo oxidative decarboxylation and produce 2 molecules of $NADH+H^{+}$.
Oxidation of 2 molecules of $NADH+H^{+}$ yields 6 ATP molecules. Oxidative decarboxylation of pyruvate results in formation of acetyl CoA.

Acetyl CoA enters the Krebs cycle which is a cyclic pathway. In one turn of Krebs cycle, 3 molecules of $NADH+H^{+}$, 1 molecule of $FAD{H}_2$ and 1 molecule of ATP are produced.
As 2 molecules of acetyl CoA are produced, there are two turns of the Krebs cycle. So, for 2 turns of Krebs cycle, 6 molecules of $NADH+H^{+}$, 2 molecules of $FAD{H}^2$ and 2 molecules of ATP are produced.

Oxidation of 1 molecule of $NADH+H^{+}$ yields 3 molecules of ATP.
Oxidation of 1 molecule of $FAD{H}_2$ yields 2 molecules of ATP.
Total ATP produced in Krebs cycle = 18 ATP (oxidation of 6 $NADH+H^{+}$) + 4 ATP (oxidation of 2 $FAD{H}_2$) + 2ATP
= 24 ATP
Thus, Krebs cycle yields 24 ATP molecules.

Oxidation of $NADH+H^{+}$ and $FAD{H}_2$ occurs in the inner mitochondrial membrane that has an electron transport chain.
Hence, during the complete oxidation of one molecule of glucose, 38 molecules of ATP are produced.