PHOTORESPIRATION//C2 PATHWAY// PHOTOSYNTHETIC CARBON OXIDATION CYCLE//GLYCOLATE CYCLE

 

Photorespiration (C2 Cycle)

 

Photorespiration is also known as C2 cycle or Glycolate cycle.

Photorespiration occurs in temperate plants like rice, beans, wheat, barley.

Photorespiration occurs only in light and responsible for release of extra CO2.

This process involves participation of Chloroplast, Peroxisome and Mitochondria.

Photorespiration increases with increasing concentration of O2.

During photorespiration, O2 is used up and CO2 is released without production of ATP or NADPH2 .

When the CO2   conc., in the atmosphere  lower  then RuBP combines  with O2  from  Phosphoglyceric Acid (PGA)  and Phosphoglycolic Acid ( Phosphoglycolate) in Chloroplast.

Phosphoglycolic acid froms Glycolic Acid (Glycolate) which transported to the Peroxisome  where glycolic acid react with O2 and formed Glyoxylic acid (Glyoxylate) and H2O2. The H2O2 is destroyed by catalase enzyme.

Glyoxylic acid is then converted into Glycine and glycine is transported out of peroxisomes and move into mitochondria where it is converted into Serine , CO2 and NH3.

The CO2 is then released in photorespiration from mitochondria and NH3   incorporated into synthesis of Glycine.

The serine returns to Peroxisome  and reduced to Hydroxypyruvic acid and finally to Glyceric acid (Glycerate).

The Glyceric acid finally enter into Chloroplast and convert into Phosphoglyceric Acid (PGA) which enters into C3 Cycle.

Note: Generally Rubisco acts as a corboxylase enzyme but in case of photorespiration it works as oxygenase enzyme.

Drawback of C2 Cycle:

1.     It uses the assimilatory power which is formed during the light reaction.

2.     It inhibit the normal process of photosynthesis.



                               The pathway of photorespiration (C2Cycle)













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