Question

In muscles, from three molecules of glucose, two are completely oxidized and one is incompletely oxidized (anaerobic) then, what will be the number of total NAD⁺ molecules utilized?
(a) 20
(b) 10
(c) 14
(d) 08

Answer 1

Hint: Glycolysis is the common step in both aerobic and anaerobic respiration where NAD⁺ is utilized when glyceraldehydes 3-phosphate forms 1, 3-diphosphoglycerate while in Krebs cycle NAD⁺ are utilized at three stages.

Complete answer:
If we consider aerobic respiration, the first step will be Glycolysis and here, 2 molecules of NAD⁺ are utilized per molecule of glucose. Between Glycolysis and Kreb’s cycle, 2 molecules of NAD⁺ are utilized. Again, in the next step of aerobic respiration i.e. the Kreb’s cycle, NAD⁺ is utilized in following reactions:
1. 2 NAD⁺ molecules are utilized when isocitrate is converted to alpha-ketoglutarate
2. 2 NAD⁺ molecules are utilized when alpha-ketoglutarate forms succinyl-CoA
3. 2 NAD⁺ molecules are utilized when malate forms oxaloacetate
Thus, for aerobic respiration, a total of 10 NAD⁺ molecules are utilized per molecule of glucose.
Now, in the anaerobic respiration, as the Glycolysis is a common step, 2 molecules of NAD⁺ will be utilized but these are regenerated in the next step and hence in the anaerobic respiration there is no net utilization of NAD⁺.
Since two glucose molecules are going in aerobic respiration and one molecule in the anaerobic respiration so the number of NAD⁺ molecules utilized will be 20.
So, the correct answer is ‘20’.

Note: The glucose molecule is completely oxidized in the process of aerobic respiration while incomplete oxidation of glucose molecule occurs in the anaerobic respiration and hence less energy is produced in the anaerobic respiration in comparison to the aerobic respiration. Krebs cycle mainly occurs in the matrix of the mitochondria.