What is an Amphibolic pathway? Why Citric acid cycle is called Amphibolic?

What does an Amphibolic pathway means?

Definition of Amphibolic pathway:

An Amphibolic pathway is a biochemical pathway that includes both anabolic and catabolic processes

(Amphi means both)

Anabolism is the synthesis of complex molecules from simpler ones with input of energy. Catabolism is the breakdown of complex molecules into simpler ones with the release of energy

Examples of Amphibolic pathway : Glycolysis, Krebs cycle,  Pentose phosphate pathway, Gluconeogenesis

These pathways play an important role in cellular metabolism as it can shift between anabolic and metabolic reactions depending on the requirement of the cell

Amphibolic pathway? Why Citric acid cycle is called Amphibolic?
Why Citric acid or Krebs cycle is called Amphibolic?

The Citric acid cycle is amphibolic; i.e., it serves as a catabolic and an anabolic pathway.

The catabolic part of Krebs cycle is the oxidation of acetyl coA forming CO2 along with GTP, NADH, FADH2.

Anabolic Reaction of Krebs cycle

Krebs cycle intermediates are used as precursors for the formation of various cellular macromolecules.

Let’s take some examples

1.Citrate+ATP+CoA→acetyl-CoA+oxaloacetate+ADP+Pi. This reaction takes place in the cytoplasm and is a source of acetyl-CoA for fatty acid biosynthesis.

2.α-Ketoglutarate + alanine↔glutamate + pyruvate.

3.α-Ketoglutarate→succinate + CO2. This reaction is involved in the hydroxylation of prolyl and lysyl residues of protocollagen, a step in the synthesis of collagen.

4.Succinyl-CoA + glycine→Δ-aminolevulinic acid (ALA). ALA is then utilized for the synthesis of heme.

5..Oxaloacetate + alanine↔aspartate + pyruvate.

As citric acid cycle serves as both anabolic and catabolic pathway; it is called amphibolic.

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