Question
Asked Sep 16, 2019
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  1. Why is the citric acid cycle called a cycle?
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Expert Answer

Step 1

Citric acid cycle is also known as Krebs cycle. It is a chain of chemical reactions. It takes place in the mitochondrial matrix and is a part of aerobic respiration. This cycle is used by all the aerobic organisms to produce energy by the oxidative metabolism of acetyl units.

Step 2

Citric acid cycle steps:

  1. In this cycle, the acetyl group from the acetyl Coenzyme A (Co-A) is linked to a four-carbon oxaloacetate molecule. This reaction produces a six-carbon citrate molecule.
  2. Citrate is oxidized through a chain of reactions. It release two CO2 molecules for each acetyl group and fed into the reaction cycle.
  3. In the whole series of reactions:
  4. i) Three molecules of Nicotinamide adenine dinucleotide (NAD+ molecules) get reduced to NADH.

ii). One molecule of flavin adenine dinucleotide (or FAD molecule) is reduced to FADH2.

iii). Depending on the cell type, either one Adenosine Triphosphate (or ATP) or Guanosine-5'-triphosphate (or GTP) molecule is produced by the process of substrate-level phosphorylation.

  1. The final product of this cycle is oxaloacetate.
Step 3

Citric acid cycle is known as a cycle because of the following reason:

As oxaloacetate is the first reactant as well as the final product of this cycle...

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