Question

Which is the correct reaction:
(a) $Pyruvic\quad acid\quad +\quad NAD^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+NAD\cdot H^{ + }+CO_{ 2 }$

(b) $Pyruvic\quad acid\quad +\quad FAD^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+FAD\cdot H^{ + }+CO_{ 2 }$

(c) $Pyruvic\quad acid\quad +\quad NADP^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+NADP\cdot H^{ + }+CO_{ 2 }$

(d) $Pyruvic\quad acid\quad +\quad NAD^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+NAD\cdot H^{ + }$

Answer 1

Hint: Formation of Acetyl Co-A is important as it enters the Krebs cycle for the acetylation of Oxaloacetic acid. Formation of Acetyl Co-A requires several coenzymes.

Complete answer:
Pyruvate which is formed by the glycolytic catabolism of carbohydrates in the cytosol, after it enters the mitochondrial matrix undergoes oxidative decarboxylation by a complex set of the reactions catalyzed by pyruvate dehydrogenase. It requires several coenzymes like NAD+ and Coenzyme A.

The reaction is:
$Pyruvic\quad acid\quad +\quad NAD^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+NAD\cdot H^{ + }+CO_{ 2 }$
Two molecules of pyruvic acid formed from one glucose molecule during glycolysis undergo the formation of two molecules of Acetyl CoA, ${ CO }_{ 2 }$ and 2NADH+2H+. This reaction is called the Link Reaction of aerobic respiration.
So, the answer is, ‘$Pyruvic\quad acid\quad +\quad NAD^{ + }\quad +\quad Co-A\quad \xrightarrow [ Mg^{ ++ } ]{ Pyruvatedehydrogenase } Acetyl\quad Co-A+NAD\cdot H^{ + }+CO_{ 2 }$.’

Note: -For aerobic respiration to take place within mitochondria the pyruvic acid formed during glycolysis is transported from the cytoplasm into the mitochondria.
- The complete oxidation of pyruvate occurs in two steps, Formation of Acetyl CoA and TCA cycle.
-The TCA cycle occurs in the inner mitochondrial matrix. The $NADH_2$ molecule formed in the process enters the ETS of the mitochondria to release energy.
-The link reaction is also known as Transition Reaction or gateway Reaction.