Which of the following best describes the reduction of the coenzyme NAD?
A. [tex]$NAD + H \rightarrow NADH$[/tex]
B. [tex]$NAD ^{+}+ H \rightarrow NADH$[/tex]
C. [tex]$NAD ^{+}+ H \rightarrow NADH _2$[/tex]
Answer (2)
The problem asks to identify the correct equation for the reduction of NAD.
Reduction involves gaining electrons or hydrogen atoms.
N A D + + H → N A DH correctly represents NAD+ gaining a hydrogen atom and an electron to form NADH.
Therefore, the correct answer is N A D + + H → N A DH .
Explanation
Understanding the Problem We need to identify the correct equation that represents the reduction of the coenzyme NAD. Reduction involves gaining electrons or hydrogen atoms. We need to check each option to see which one correctly shows NAD gaining a hydrogen atom and an electron to form NADH.
Analyzing Option 1 Let's analyze the first option: N A D + H r i g h t a rro wN A DH . This equation seems to balance in terms of atoms, but it doesn't explicitly show the charge aspect of the reduction. NAD is not usually written without a charge when it's being reduced.
Analyzing Option 2 Now let's analyze the second option: N A D + + H r i g h t a rro wN A DH . This equation shows that N A D + gains a hydrogen atom and an electron (implicitly) to become NADH. The positive charge on N A D + is neutralized, which is consistent with reduction.
Analyzing Option 3 Finally, let's analyze the third option: N A D + + H r i g h t a rro wN A D H 2 . This equation shows N A D + gaining a hydrogen atom to become N A D H 2 . While it might seem like a reduction by gaining hydrogen, the standard reduced form of NAD is NADH, not N A D H 2 . Also, balancing charges would be an issue here.
Conclusion Based on the analysis, the second option, N A D + + H r i g h t a rro wN A DH , best describes the reduction of the coenzyme NAD because it correctly represents the gain of a hydrogen atom and an electron to form NADH, while also balancing the charge.
Examples
In cellular respiration, NAD acts as an electron carrier. The reduction of N A D + to NADH is a crucial step in glycolysis, the Krebs cycle, and the electron transport chain. NADH then donates these electrons in the electron transport chain to generate ATP, the energy currency of the cell. Understanding this reduction is key to understanding how cells produce energy.
The best description of the reduction of the coenzyme NAD is given by the equation NAD^+ + H → NADH. This correctly shows NAD in its oxidized form gaining a hydrogen atom and an electron to become NADH. Therefore, the correct answer is Option B.
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