Dr. Mahesha H B Associate Professor and Head Department of Sericulture Yuvaraja s College University of Mysore, Mysuru, India

Transcription

1 PHOTOSYNTESIS Dr. Mahesha H B Associate Professor and Head Department of Sericulture Yuvaraja s College University of Mysore, Mysuru, India 1

2 PHOTOSYNTHESIS The process in green plants and certain other organisms by which carbohydratesare synthesized from carbon dioxide and water using lightas an energy source. Or The synthesis of complex organic material using carbon dioxide, water, inorganic saltsand light energy (from sunlight) captured by lightabsorbing pigments such as chlorophylland other accessory pigments. 2

3 6 CO ATP+12 12H 2 O+12 NADPH + / 2H + C 6 H 12 O Pi + 18 ADP + 12 NADP + + 6(O 2 ) 12 According to Biological Economists ALL WEAALTH ORIGINATES DIRECTLY OR INDIRECTLY AS A CONSEQUENCE OF PHOTOSYNTHESIS 3

4 Photosynthesis is the biggest photochemical & biochemical phenomena acting as a master key for the existanceof life on this globe. Inturnsolar energy is the chief driver of this reaction 4

5 Nature of radiant energy 5

6 ELECTROMAGNETIC SPECTRUM OF SUN LIGHT nm induces sensation in photosynthesis 6

7 Photochemical Changes in Chlorophyll A. Loss as heat. B. Loss of light. C. Resonance energy transfer. D. Energy transduction 7

8 Photochemical Changes in Chlorophyll 8

9 Photosynthetic pigments Chlorophyll a, b, c, d, e, bacteriochlorophyll Carotenoids β carotene Xanthophylls Phycobilins - Phycocyanin Phycoerythrin 9

10 Absorption Spectra of Photosynthetic pigments 10

11 Site of Photosynthesis The light reactions of photosynthesis, are associated with the thylakoid membranes. In contrast, the lightindependent reactions, or so-called dark reactions, notably CO2 fixation, are located in the stroma. 11

12 PHOTOSYNTHETIC UNIT AND PHOTOCHEMICAL REACTION CENTRE 12

13 Steps/out line of Photosynthesis Light Reactions of Photosynthesis converts solar energy into potential energy. The light reaction converts ADPand NADP + into the ATPand NADPHand produces oxygen. Cyclic Phosphorylation: Non-cyclic Phosphorylation: Calvin Benison Cycle of Photosynthesis The light independent reactions fixes CO2in to C 6 H12O 6 using the products of light reaction 13

14 Photosystems The photochemical phase requires the interaction of 2 photosystems. Photosystem I: consists ~200 light harvesting chlorophylls, ~50 Carotenoids, a mol. of P700, 1 mol. of an unidentified compound (X), one cytochrome f, one plastocyanin, two cytochrome b 563, Ferredoxin reducing substance and 1/2 membrane bound ferredoxin molecule. ItproducesastrongreductantwhichreducesNADP + tonadph 2+. Photosystem II: consists~200 light harvesting chlorophylls, ~50 Carotenoids, a trapping chlorophyll mol. of P680, one mol. of an unidentified compound (Z), a plastoquinone, ~4 plastoquinone equivalents, 3 mn mole., two cytochrome b 559 and chloride. ThesystemisconcernedwiththereleaseofO 2. InassociationbothI&IIproduces,ATPandNADPH. 14

15 Mechanism of Light Reaction Photophoshoriyation: The synthesis of ATP from ADP and phosphate that occurs in a plant using radiant energy absorbed during photosynthesis: ADP + pi ATP Photolysis of Water: 4H 2 O --->4H + + 4OH - 4OH - 2H 2 O 2 2H 2 O + O 2 15

16 Cyclic Photophosphorylation Redox potential: The tendency to release and acceptance of electrons. Expressed in volts/milivolts. The term Redox has been derived from Reduction-Oxidation. 16

17 Non cyclic photophosphorylation 17

18 Non cyclic photophosphorylation X Q 4H 2 O --->4H + + 4OH - 4OH - 2H 2 O 2 2H 2 O + O 2 18

19 Dark reaction/c3 cycle/calvin Benson reaction/ Blackman reaction 19

20 Reaction steps of C3 cycle 20

21 Out line of C 3 cycle reactions Glyceric acid 3 Phosphate 3 phosphoglyceric acid 1,3 bisphosphoglyceric acid Ribulose 1,5 bisphosphate Fructose 1,6 bis phosphate Ribose 5 Phosphate Dihydroxy acetone p Ribulose 5 Phosphate Fructose 6 Phosphate Xylulose 5 Phosphate Sedoheptulose 7 Phosphate Sedoheptulose 1,7 bisphosphate Erythrose 4 Phosphate Glucose 6 Phosphate 21

22 Out line of C 3 cycle reactions 22

23 THE OVERALL REACTION OF PHOTOSYNTHESIS 6 CO ATP + 12 H 2 O + 12 NADPH + / 2 H + C 6 H 12 O Pi + 18 ADP + 12 NADP + +6O 2 23

24 C 3 Plants A plantthat utilizes the C 3 carbon fixation pathway as the sole mechanism to convert CO 2 into an organic compound(i.e. 3- phosphogylycerate). 24

25 C 4 Plants A plant that utilizes the C 4 carbon fixation pathway in which the CO 2 is first bound to a phosphoenolpyruvate in mesophyll cell resulting in the formation of four-carbon compound (oxaloacetate) that is shuttled to the bundle sheeth cell where it will be decarboxylated to liberate the CO 2 to be utilized in the C 3 pathway. 25

26 Kranz Anatomy 26

27 27

28 Tansaminase Aspartate Oxaloacetate Aspartate Tansaminase 28

29 Photorespiration The processby which in the presence of lightplant consumes oxygen and releases carbon dioxide(in stead of fixing (CO 2 ) during Photosynthesis, resulting in a decrease in Photosynthetic output. 29

30 Photorespiration Pathway Glycine Glyoxolate Glycolate Serine Phosphoglycolate Hydroxypyruvate 30

31 Photorespiration Pathway Rubisco Kinase α-oh reductase Oxidase Transamination Catalase > H 2 O+O Released in photorespiration 31

32 Acknowledgements to INTERNET FOR PICTURES AND PHOTOGRAPHS 32