Question

NADH is a high energy electron carrier molecule. During which reactions is NADH produced?
I. Glycolysis
II. Krebs cycle
III. Conversion of pyruvate to Acetyl-CoA

• A. I only
• B. II only
• C. I and II only
• D. l and Ill only
• E. I, II, and III

Answer 1

Answer: (E)

I, II, and III

I. Glycolysis is basically an anaerobic pathway as it does not use oxygen. It is an enzyme controlled 10 steps reaction by which glucose, fructose or sucrose is reduced to form pyruvic acid with the production of ATP and NADH₂.

II. Krebs cycle is basically a catabolic reaction as it oxidizes acetyl Co-A and organic acids into C‎O₂ and H₂O. One molecule of pyruvic acid after entering into mitochondrion undergoes three decarboxylation and five oxidation steps. On oxidation, one molecule of pyruvic acid through Krebs cycle yields 15 ATP. Krebs cycle involve eight steps to oxidise two molecules of acetyl Co-A produced in transition reaction completely into 4C‎O₂, 10H₂O , 2ATP, 2FADH₂ and 6NADH + H⁺.

III. In the presence of O₂, pyruvic acid is further degraded into Acetyl Co-A in mitochondrion with the help of enzyme pyruvate dehydrogenase. This reaction produces C‎O₂ and reduction of NAD⁺ to NADH₂ takes place.

Hence NADH is produced in all the processes given in the question.

So, the correct answer is 'I, II and III'.