C3 cycle

introduction
stages
signification of c3 cycle

1. C3 CYCLE Presented by : - Salvi Pinky P. M.sc sem : - 3 Paper : - Botany 503 Department of Life sciences, H. N. G. U., Patan

2. CONTENTS Introduction Stages : — 1) Fixation 2) Reduction 3) Regeneration Significance of C3 cycle Difference between C3 and C4 cycle

3. Introduction It is a cyclic reaction occuring in the dark phase of photosynthesis. In this reaction CO2 is converted in to sugar and hence it is a process of carbon fixation. The Calvin cycle was first observed by Melvin Calvin in chlorella, unicellular green algae. Calvin was awarded Nobel prize for this work in 1961.

4. Other names for Calvin Cycle : — 1) Dark reactions C3 Cycle 3 ) Reductive Pentose phosphate Cycle 4 ) Calvin Cycle 5 ) Photosynthetic Carbon Reduction Cycle [ PCR ]

5. Calvin and other workers are working at the University of Berkeley, he used a carbon – 14 isotopes to understand the Photosynthesis process in plants. This radioactive isotope helped him determine how the light independent reaction works in Singal – celled algae. Calvin and co - workers found that after three second, radioactivity appeared in phosphoglyceric acid or PGA. Phosphoglyceric acid is, therefore, the first stable product of Photosynthesis as known as C3 Cycle .

6. Stages of C3 cycle These energy carrying molecules are made in the stroma of the chloroplast where the Calvin takes place. The Calvin cycle is not totally independent of light since it relies on ATP and NADPH, which are products of the light dependent reactions. The light reactions of the Calvin cycle can be organised in to three basic stages : - 1) Fixation 2) Reduction 3) Regeneration

7. FIXATION In the stroma, in addition to CO2, two other components are present to initiate the light independent reactions : an enzyme called ribulose Bi phosp hate carboxylase( RUBISCO) and three molecules of Ribulose bisphosphate (RUBP). RUBP has five atoms of carbon, flanked by two phosphatase. For each CO2 molecules that reacts with one RUBP, two molecules of 3 phosphoglyceric acid ( 3 PGA) from, 3 PGA has three carbons and one phosphate.

8. Each turn of the cycle involves only one RUBP and one carbon dioxide and forms two molecules of 3 - PGA. 3 phosphoglyceric acid ( PGA ) is the first stable product of Calvin cycle. This prosses is called carbon fixation because CO2 is " fixed" from an inorganic form into organic molecules. 3 unstable intermediate 6C + 3 H2O Carbon 3 phoshpo- Compound dismutase glyceric acid

9. REDUCTION 6 molecules of 3 PGA are phosphorylated by 6 molecules of 1, 3 diphosphoglyceric acid and 6 molecules of ADP. Six molecules of 1,3 diphosphoglyceric glyceric acid are 6 molecules of 1, 3 diphosphoglyceric acid are reducedhe use of molecules of NADPH2 to from 6 Molecules of 3 phosphoglyceric. 3 Phospho Kinase 1,3 diphosphate glyceric acid + ATP glyceric acid + ADP

10. 1,3 diphospho Triose phosphate + NADPH2 Dehydrogenase glyceric acid 3 Phospho + NADP + H3 PO4
glyceraldehyde

11. REGENERATION In the regeneration phase, the ribose diphosphate is regenerated it involves the following steps. Some of the molecules of 3 phosphoglyceraldyde convert into dihydroxy acetone phosphate ( DHAP ). 3 Phospho Triose phosphate Dihydroxy acetone isomerase Phosphate glyceraldehyde ( DHAP )

12. 2. Both 3 PGAL and DHAP then unite in the presence of enzyme, aldolase to from fructose 1,6 diphosphate. 3. Fructose 1,6 d isphosphate is converted into Fructose 6 phosphate in the presence of phosphorylase. 4. Some of the 4 phosphate combines with DHAP in the presence of the enzyme aldolase to form sedoheptose 1,7 diphosphate. 3 Phospho Aldolase Fructose 1,6
glyceraldehyde + DHAP diphosphate

13. 5. 3PGAL react with Fructose 6 phosphate in the presence of enzyme transeketolase to from erythrose 4 phosphate and xylulose 5 phosphate. 6. Erythrose 4 phosphate combines with DHAP in the presence of the enzyme aldolase to form sedoheptose 1,7 diphosphate. 3 Phospho Fructose 6 Trans Erythrose 4 glyceraldehyde + phosphate ketolase phosphate + Xylulose 5 phosphate

14. 7. Sedoheptulose 1,7 diphosphate loses one phosphate group in the presence of the enzyme phosphatase to from sedoheptulose 7 phosphate. 8. Sedoheptulose 7 phosphate react with 3 PGAL in the presence of transeketolase to form xylulose 5 phosphate and ribose 5 phosphate. Erythrose 4 Aldolase Sedoheptulose 1,7 phosphate + DHAP diphosphate

15. 9. Ribose 5 phosphate is converted into Ribulose 1,5 bisphosphate in the presence of enzyme phosphopentose kinese and ATP. Sedoheptulose + 3 Phospho Trans Xylulose 7 phosphate Glyceraldehyde Ketolase 5 phosphate + Ribose 5 phosphate Ribose + ATP Phospho Ribulose 5 phosphate pento 1,5 di- + ADP kinese Phosphate

16. 10. Two Molecules of xylulose 5 phosphate are also converted into one molecule of Ribulose 5 phosphate. Ribulose 5 phosphate is phosphorylated by ATP to form Ribulose 1,5 bisphosphate and ADP. 2 moles Phosphopento 2 moles Xylulose + ATP Kinese Ribulose + ADP 5 phosphate 1,5 diphosphate

17. Net reaction : — 3CO2 + 5H2O + 6NADPH + 9ATP glyceraldehyde - 3 - phosphate + 6NADP+ + 3H+ + 9 ADP + 8Pi

18. SIGNIFICANCE OF C3 CYCLE It is the main biochemical pathway during the dark reaction (phase – II) of Photosynthesis. It result in the synthesis of carbohydrates from CO2 [ assimilation of carbon ]. It depends on the light reaction ( phase I ) for the supply of the assimiatory power ( ATP and NADPH2 ) required for carbon assimilation.

19. It stores the ATP energy formed during light reaction in the carbohydrate molecules as the food energy. It is the primary source of organic food and food energy for all the organisms. Calvin cycle [ C3 cycle ] reaction occur in all photosynthetic plants ; i.e. C3, C4 and CAM plants, during the dark phase of Photosynthesis.

20. DIFFERENT BETWEEN C3 AND C4 CYCLE

21. REFERENCES Plant physiology By : - Taize & Zeiger Plant physiology By : - Verma P. S. and P. K. Agarwal Principles of biochemistry By : – Albert lehninger https:// biologydictionary.net https:// eagri.org www.losal.org

22. Thank you