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Regulation of calvin cycle

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Regulation of calvin cycle

  1. 1. Presented by: Muhammad Usman Mughal Roll Number: 25 Class: Msc Botany 3rd Semester Session: 2013-2015
  2. 2. 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
  3. 3. 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 4
  4. 4.  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
  5. 5. 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 6
  6. 6.  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
  7. 7.  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
  8. 8.  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
  9. 9.  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
  10. 10.  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
  11. 11.  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
  12. 12.  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
  13. 13. 4-Dec-14Regulation of calvin cycle by: Muhammad Usman Mughal 14
  14. 14. 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
  15. 15. 4-Dec-14 Regulation of calvin cycle by: Muhammad Usman Mughal 16

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