TCA Cycles

What is TCA cycle?

TCA stands for Tri Carboxylic Acid. TCA cycle is one of the metabolic pathways for aerobic organism. This process carried out in the cyclic manner, that's why it is called TCA cycle. This cycle is called by other names; they are 'Citric acid cycle', because the initial formed product is Citric acid, which is tricarboxylic acid and it is the naming reason for TCA cycle. One more name is Krebs cycle named after the scientist Adolf Hans Krebs

Schematic representation of TCA cycle:

Step wise explanation of krebs cycle:

• Oxalo acetic acid is the final product of krebs cycle; to initiate next cycle acetyl coA should be added to OAA to produce Citric acid. This reaction is catalysed by citrate synthetase.
• Citric acid is converted into its isomeric form called iso-citric acid. This reaction is catalysed by aconitase. Here, hydration and dehydration takes place.
• Iso-citric acid is converted into alpha - keto glutarate. This reaction is catalysed by iso citrate dehydrogenase. Here, oxidation and decarboxylation takes place.
• alpha - keto glutarate is converted into succinyl coA. This is facilitated by alpha - keto glutarte dehydrogenase. Here, oxidative decarboxylation takes place.
• Succinyl coA is converted into succinic acid. This is done by succinly coA synthetase. Here, substrate level phosphorylation takes place.
• Succinic acid is converted into fumaric acid. This is done by succinate dehydrogenase. Here, oxidation takes place.
• Fumaric acid is converted into malic acid by fumarase and hydration takes place here.
• Malic acid is converted into oxalo acetic acid (OAA) by malate dehydrogenase with the help of oxidation.
• Oxalo acetic acid again combine with acetyl coA to form citric acid to continue the cycle.

Significance of TCA cycle:

• It is the essential metabolic pathway for all types of food stuffs such as carbohydrates, proteins, lipids.
• It possess substrate level phosphorylation i.e., formation of ATP in the middle of the reaction without the help of electron carriers.