Short Notes For Neet Glycolate Pathway

The Glycolate Pathway, also known as the C2 Cycle of Photosynthesis, Photorespiration or Glycolate-Glyoxylate Metabolism, reduces the Photosynthesis efficiency of C3 Plants. Additionally, Glycolate Metabolism is also found in Unicellular Green Algae.

The 2-phosphoglycolate cycle helps in removing a toxic metabolite produced by the oxygenation reaction of RuBisCO. It produces PGA eventually, but ~25% of C is released as CO2 in the process and ATP is also utilised.

Key Features of Glycolate Pathway

  • Involves the oxidation of glycolate to glyoxylate
  • Involves the conversion of glyoxylate to glycine
  • Involves the conversion of glycine to serine
  • Involves the conversion of serine to pyruvate

The process competes with photosynthesis, resulting in the wastage of some of the energy produced.

It occurs in Chloroplast, Peroxisomes, and Mitochondria.

RuBisCO, the main enzyme of the Calvin cycle, has an affinity for both CO2 and O2, and they both compete for binding with RuBisCO. The binding of either species is dependent on the concentration of both of them, and at mild temperatures, RuBisCO has a higher affinity for carbon dioxide.

The process begins when O2 binds with RuBisCO, an enzyme that oxygenates RuBP (Ribulose-1,5-bisphosphate), resulting in the formation of 2-phosphoglycolate and 3PGA (3-phosphoglycerate). This process takes place in the chloroplast.

The production of 3PGA has been decreased, and it is now part of the Calvin cycle.

Glycolate oxidase is the enzyme that catalyses the reaction of 2-phosphoglycolate being translocated to peroxisomes and being oxidised to glyoxylate by hydrogen peroxide (H2O2).

Catalase breaks down Hydrogen Peroxide into Water and Oxygen.

Glyoxylate is converted to Glycine in peroxisomes by Glutamate-glyoxylate Aminotransferase.

Glycine is transported to mitochondria.

In mitochondria, an enzyme called Glycine decarboxylase catalyzes the conversion of two Glycine molecules (2C) into a Serine (3C), with CO2 and NH3 being released in the process.

Serine is transported back to peroxisomes, where it is then converted to Glycerate.

Glycerate is transported back to the chloroplast, where it is phosphorylated to form 3PGA. ATP is used in this reaction. 3PGA then enters the Calvin cycle.

It is important to note that RubisCO has a higher affinity for oxygen at increased temperatures, resulting in a higher rate of photorespiration in hot and dry environments. To counteract this, C4 plants and CAM plants have evolved different mechanisms for carbon fixation; these plants accumulate carbon dioxide around RuBisCO to suppress its oxygenation activity.

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