Photorespiration c2 cycle

Photorespiration - Introduction, why is it occur in plants, pathway of photorespiration, Enzymes names, pathway step by step explanation, Benefits of photorespiration, additional information related to photorespiration, Rubisco enzyme, Oxygenase enzyme, Oxygen concentration higher leads to photorespiration, problem to carry out calvin cycle.

1. Photorespiration (C2 Cycle) Jasmine Juliet .R Biochemistry Agricultural College & Research Institute, Madurai.

2. Photorespiration - Introduction Photorespiration is a metabolic pathway that occurs in photosynthetic organisms and releases carbon dioxide, consumes oxygen, and produces no chemical energy or food . This process limits the growth rates of plants . Photorespiration generally occurs on hot, dry, sunny days causing plants to close their stomata and the oxygen (O 2 ) concentration in the leaf to be higher than the carbon dioxide (CO 2 ) concentration.

3. Photorespiration(C2 cycle)

4. Photorespiration - Introduction When a plant leaf contains a high concentration of oxygen, instead of carbon dioxide, this poses a problem for the normal photosynthetic process , including the light reactions and the Calvin cycle.

5. Photorespiration - Oxygenase Photorespiration involves the light dependent uptake of O 2 and evolution of CO 2 during photosynthesis in green plant tissues. The first step in photorespiration is associated with the oxygenase activity of the photosynthetic enzyme Rubisco .

6. Photorespiration(C2 cycle)

7. Photorespiration - Pathway The reactions of photorespiration cycle occur in three organelles : chloroplasts, peroxisomes , and mitochondria . The C2 cycle is initiated in the chloroplast with the formation of 2-phosphoglycolate , which is subsequently converted to glycolate and Pi by the action of phosphoglycolate phosphatase . The glycolate exits the chloroplast and enters into the peroxisome .

8. Photorespiration - Pathway The glycolate reacts with O 2 to produce glyoxylate and H 2 O 2 which is catalysed by glycolate oxidase . Two molecules of glyoxylate are aminated to form glycine in a reaction catalysed by glutamate:glyoxylate aminotransferase . H 2 O 2 is removed by the abundant catalase present in peroxisomes to H 2 O and O 2 .

9. Photorespiration - Pathway The glycine produced in the peroxisome moves into the mitochondria. For every two molecules of glycine , one molecule of serine, CO 2 and NH 3 is produced , and one NAD + is reduced to NADH. This takes place through the action of glycine decarboxylase complex. One CO 2 is produced for every two molecules of O 2 taken up by the action of RuBP oxygenase .

10. Photorespiration - Pathway The serine produced in the mitochondria now moves into the peroxisome , where it is deaminated to hydroxypyruvate by serine:glyoxylate aminotransferase . Then, hydroxypyruvate is reduced to glycerate by hydroxypyruvate reductase . The glycerate exits the peroxisome and enters the chloroplast and is phosphorylated by glycerate kinase to 3-phosphoglycerate. This reaction completes the conversion of two molecules of phosphoglycolate to one of 3-PGA , which can now enter the C3 cycle.

11. Photorespiration (C2 cycle)

12. Photorespiration - Benefits Photorespiration have some benefits for plants. There's some evidence that photorespiration can have: Photoprotective effects (preventing light-induced damage to the molecules involved in photosynthesis), Help maintain redox balance in cells , and Support plant immune defenses .

13. Photorespiration (C2 cycle) Additional information:   The 2-phosphoglycolate is a very toxic product and cell cannot metabolise it . So, to bypass this photorespiration takes place in some higher plans.

14. Videolinks https://www.youtube.com/watch?v=fWsU4_Zau0c https://www.youtube.com/watch?v=gtNL1U6j5ZM https://www.youtube.com/watch?v=Xxf5aqvFlNs https://www.youtube.com/watch?v=xW-VkFyxmhg

15. Thank you