Regulation of calvin cycle
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This presentation discusses the regulation of the Calvin cycle by Muhammad Usman Mughal. It begins with an introduction to the Calvin cycle and then examines four main systems that regulate the cycle: 1) the rubisco enzyme activation system, 2) the ferredoxin-thioredoxin system, 3) ionic movement that modulates enzymes, and 4) the formation of supramolecular enzyme complexes. It focuses on how light and carbon dioxide levels affect these regulatory systems and the activities of key Calvin cycle enzymes.
Regulation of calvin cycle
- 2. Presented by: Muhammad Usman Mughal Roll Number: 25 Class: Msc Botany 3rd Semester Session: 2013-2015
- 3. 1. Introduction 2. What is calvin cycle? 3. What is regulation of calvin cycle? 4. Rubisco enzyme activation system 5. Ferredoxin-thioredoxin system 6. Ionic movement modulate the enzymes 7. Formation of supramolecular complexes 8. Conclusion 9. References 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 3
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- 5. Carbon fixation cycle/ Reductive pentose phosphate cycle/ Calvin Benson cycle/ C3 cycle Series of biochemical redox reactions in stroma of chloroplast Independent of light CO2 convert into carbohydrates in the presence of ATP,NADPH Opposite to Kreb cycle/ citric acid cycle 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 5
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- 7. The rate of calvin cycle does not remain constant All intermediates present in adequate concentration in light e.g CO2, ATP, NADPH, ions, Enzymes Turned off when not needed in dark Mainly regulate by the amount of enzymes in stroma Light modulates the expression of stromal enzymes via specific photoreceptor (phytochrome and blue light receptor) Structure and activity of enzyme modified by two methods 1) covalent bonds 2) ionic composition 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 7
- 8. Calvin cycle itself independent of light but the enzymes which regulate calvin cycle are dependent on light Light dependent modulation mechanism change the activity of five key enzymes 1. Rubsico 2. Fructose-1,6-bisphosphatase 3. Sedoheptul0se-1,7-bisphosphatase 4. Phosphoribulokinase 5. NADPH-glyceraldehyde-3-phosphate dehydrogenase Generally there are four regulation systems 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 8
- 9. Ribulose bisphosphate carboxylase Most abundant protein on the earth to date Activity of Rubisco increases in the light CO2 play dual role in the activity of rubisco 1) activate the enzyme 2) substrate for carboxylation 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 9
- 10. Light controls the activity of four remaining enzyme via ferredoxin-thioredoxin system 1. Fructose-1,6-bisphosphatase 2. Sedoheptul0se-1,7-bisphosphatase 3. Phosphoribulokinase 4. NADPH-glyceraldehyde-3-phosphate dehydrogenase 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 10
- 11. Ferredoxin-thioredoxin system consist of 1. Ferredoxin 2. Ferredoxin-thioredoxin reductase 3. Thioredoxin (regulatory protein) Thioredoxin protect against damage caused by reactive oxygen species (H2O2, O2-,OH-) 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 11
- 12. Due to illumination of light H+ moves from stroma to thylakoid space (pH of stroma increases from 7 to 8) In this response of hydrogen ions, Mg2+ moves from thylakoid space to stroma (formation of E-carbamate complex) Enzymes require Mg2+ are more active at pH 8 than 7 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 12
- 13. Enzyme Phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) bound to CP12 (protein) with the help of disulfide bonds to hold the complex (supramolecular complex) 4-Dec-14 13Regulation of calvin cycle by: Muhammad Usman Mughal
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- 15. Taiz, T. and Zeiger, E. 2006, Plant physiology, 4th Edition, pp 205 to 208. https://www.boundless.com/microbiology/textbook s/boundless-microbiology-textbook/microbial- metabolism-5/biosynthesis-52/regulation-of-the- calvin-cycle-339-7097/ http://en.wikipedia.org/wiki/Light- independent_reactions#Light-dependent_regulation http://5e.plantphys.net/article.php?ch=8&id=81 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 15
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