Question

How many times does decarboxylation occur in the aerobic breakdown of one glucose molecule and when does it occur?

Answer 1

Hint :Decarboxylation is indeed a chemical reaction in which a carboxyl group is removed and carbon dioxide is released. Decarboxylation is usually described as a reaction between carboxylic acids that removes a carbon atom from a carbon chain. Carboxylation, or the addition of $ C{O_2} $ to a compound, is the reverse process, and is the first chemical step in photosynthesis.

Complete Step By Step Answer:
During the aerobic breakdown of one glucose molecule, decarboxylation happens six times.
Each of the six carbon atoms in a glucose molecule must be converted into $ C{O_2} $ .
The glucose molecule gets split into two three-carbon fragments during glycolysis (pyruvate).
In a preparatory step, these fragments are fed into the Tricarboxylic Acid Cycle.
Preparatory Step:
As pyruvate is converted into $ Acetyl - CoA $ by pyruvate dehydrogenase, the first carbon atom of pyruvate is removed as $ C{O_2} $ .
 $ \underbrace {C{H_3}COCO{O^ - }}_{pyruvate} + NA{D^ + } + H - SCoA\xrightarrow[{dehydrogenase}]{{pyruvate}}NADH + C{O_2} + \underbrace {C{H_3}CO - SCoA}_{Acetyl - CoA} $
Tricarboxylic Acid Cycle:
The Tricarboxylic Acid Cycle is shown in detail.

In Steps $ 3 $ and $ 4 $ of the Tricarboxylic Acid Cycle, the remaining two carbons are lost as $ C{O_2} $
Step $ 3 $ . Isocitrate to $ \alpha - ketoglutarate $
In this step, the second $ C{O_2} $ molecule is formed.
 $ \underbrace {\mathop O\limits^ - COH\left( {OH} \right)C\left( {CO{O^ - }} \right)C{H_2}CO{O^ - }}_{isocitrate} + NA{D^ + }\xrightarrow[{dehydrogenase}]{{isocitrate}}\underbrace {\mathop O\limits^ - COCOCH\left( {CO{O^ - }} \right)C{H_2}CO{O^ - }}_{oxaloacetate} + NADH + {H^ + } $
 $ \underbrace {\mathop O\limits^ - COCOCH\left( {CO{O^ - }} \right)C{H_2}CO{O^ - }}_{oxaloacetate} + NADH + {H^ + }\xrightarrow[{dehydrogenase}]{{isocitrate}}\underbrace {\mathop O\limits^ - COCOC{H_2}C{H_2}CO{O^ - }}_{\alpha - ketoglutarate} + C{O_2} $
Step $ 4 $ . $ \alpha - ketoglutarate $ to $ succinyl - CoA $
In this step, the third $ C{O_2} $ molecule is formed.
 $ \underbrace {\mathop O\limits^ - COCOC{H_2}C{H_2}CO{O^ - }}_{\alpha - ketoglutarate} + CoASH + NA{D^ + } \\
  \xrightarrow[{dehydrogenase}]{{\alpha - ketoglutarate}}\underbrace {CoA - S - COC{H_2}C{H_2}CO{O^ - }}_{succinyl - CoA} + C{O_2} + NADH \\ $

Note :
The Tricarboxylic acid cycle (TCA cycle), also known as the Krebs cycle or the citric acid cycle, is the second stage of the three-stage mechanism by which living cells break down organic fuel molecules which is in the presence of oxygen to harvest the energy they need to expand and divide.