PHOTOSYNTHESIS.pdf
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details of pigments, light reaction and dark reaction
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PHOTOSYNTHESIS.pdf
- 1. PHOTOSYNTHESIS Harvesting the Solar Energy 1 PHOTOSYNTHESIS
- 4. CONTENT ✓Definition ✓Photosynthetic pigments ✓Process- 4 PHOTOSYNTHESIS •HILL REACTION •RED-DROP & EMERSON EFFECT •PHOTOSYSTEMS •Z-SCHEME LIGHT REACTION •CALVIN CYCLE •HATCH & SLACK PATHWAY •CAM PATHWAY DARK REACTION
- 6. PIGMENTS ➢ Requires absorption of light ➢ PIGMENTS- ➢ CHLOROPHYLL – Primary pigment ➢ CAROTENOIDS – accessory pigment ➢ PHYCOBILINS – accessory pigment 7 PHOTOSYNTHESIS
- 7. CHLOROPHYLL ➢ Chl. a, Chl. b, Chl. c, Chl. d, Chl. e, Bacteriochl. etc. ➢ Porphyrin derivative ➢ Cyclic tetrapyrrolic str. ➢ Porphyrin ring & Phytol tail ➢ Empirical formula- Chl.a – C55 H72 O5 N4 Mg Chl.b – C55 H70 O6 N4 Mg ➢ Peaks of absorption – Chl. a - 662 & 430 nm Chl. b - 642 & 454 nm 8 PHOTOSYNTHESIS
- 11. CAROTENOIDS ➢ Orange-Yellow pigments ➢ 2 types- Carotenes Xanthophylls -Orange - Red -Yellow -Most common-β Carotene - Oxygenated carotenes ➢ Absorb λ not absorbed by Chl. ➢ Prevents photo-oxidation of Chl. by absorbing excess light energy 12 PHOTOSYNTHESIS
- 12. PHYCOBILINS ➢ Open chain tetrapyrroles ➢ Water sol. complexes of proteins & bile pigments ➢ Red algae & Cyanobacteria ➢ 3 Photosynthetic Phycobilins- *Phycocyanin *Phycoerythrin *Allophycocyanin 13 PHOTOSYNTHESIS
- 13. PROCESS ➢ Oxi.-Red. Reaction - H2O oxi O2 CO2 red. Carbohydrates ➢ 6CO2+12H2O C6H12O6+6O2+6H2O 14 PHOTOSYNTHESIS
- 14. LIGHT REACTION ➢ Site – Grana (Thyllakoid membrane) ➢ Dependent on light ➢ Water – oxidised ➢ Oxygen – evolved ➢ Energy produced as ATP & NADPH 15 PHOTOSYNTHESIS
- 15. HILL REACTION: ✓ The source of oxygen which is evolved during the photosynthesis is water. In 1937, an English bio-chemist named, Robin Hill proved this idea by a reaction. This reaction is named as Hill reaction. ✓ Isolated chloroplast release O2 in presence of suitable electron acceptor (Hill reagent DCPIP) ✓ Light driven split of water in absence of CO2 fixation-Hill reaction ✓ Ruben & Kamen (1940s)- 6CO2+12H2O18 C6H12O6+6O2 18+6H2O 16 PHOTOSYNTHESIS
- 16. RED DROP & EMERSON ENHANCEMENT EFFECT: ✓ 2 quanta light energy – required – drive 1 electron from water to NADP+ ✓ for red. of 1 CO2 – 4 electrons ✓ Therefore 8 quanta -1 CO2 red./1O2production ✓ No. of oxygen mol. released = Quantum Yield Quanta = 1/8 18 PHOTOSYNTHESIS
- 17. ✓ Emerson & Lewis – *Q.Y. decreases sharply – λ ˃ 680nm (red zone) - Red Drop *If λ ˂ & ˃ 680nm provided simultaneously – Q.Y. much greater than could be from adding rates when either λ was provided alone – Emerson enhancement effect 19 PHOTOSYNTHESIS
- 20. COMPONENTS OF LIGHT REACTION PHOTOSYSTEMS LIGHT HARVESTING COMPLEXES *Chl.a,chl.b,xanthophyll *little βcarotene *assists in light absorption ATPase COMPLEX/COUPLING FACTOR *catalyses ATP synthesis 22 PHOTOSYNTHESIS PS I •Stroma thylakoids •Chl.a,chl.b,βcarotene •Reaction centre P700 •Plastocyanin,FRS PS II •Grana thylakoids •Chl.a,chl.b,βcarotene •P680,phaeophytin •Plastoquinone,Mn proteins •Cyt.b6f ccomplex
- 22. -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 PS II P680 Phaeo PSI P700 P430 H2O 1/2O2+2H + e- PQ Cytb6f PC FR S Fd NADP NADPH NON-CYCLIC ELECTRON TRANSPORT CHAIN PHOTOSYNTHESIS 24
- 24. PHOTOPHOSPHORYLATION ➢ Formation of ATP in presence of light ➢ Mechanism – *Chemical coupling hypothesis - Slater *Conformational coupling hypo. - P. D. Boyer *Chemi-osmotic coupling hypo. - P. Mitchell 27 PHOTOSYNTHESIS
- 26. DARK REACTION ➢ Reductive Pentose Phosphate pathway / Calvin Cycle / Bassham & Calvin Cycle / Blackman Reaction / Photosyn. Carbon Reduction Cycle / C3 Cycle ➢ Steps- 29 PHOTOSYNTHESIS Synthesis of Carbohydrates Regeneration of RuBP
- 27. 6 RuBP 12 3PGA 12 G3P 3 G3P + 3 DHAP 3 FDP 3 F6P 2 F6P + 2 G3P 2 X5P + 2 E4P 2 E4P + 2 DHAP 2 SDP 2 S7P + 2 G3P 2 R5P + 2 X5P 4 X5P + 2 Ru5P 6 Ru5P 6CO2 RuBP Carboxylase 12NADPH 12ATP 12NADP 12ADP G3P Dehydrogenase PGA Kinase Isomerase FDP Aldolase Hexose Diphosphatse 3 iP G6P Glucose P Isomerase GLUCOSE Phosphatase iP Aldolase Diphosphatase 2 iP Transketolase Ribose P Isomerase Ribose P Epimerase 6ATP 6ADP 30 PHOTOSYNTHESIS
- 28. HATCH & SLACK PATHWAY / COOPERATIVE PHOTOSYNTHESIS / C4 PATHWAY ➢ Eg. Saccharum, Zea mays, Amaranthus, Atriplex, Cyperus etc. ➢ C4 plants – Specific anatomical, Physio. & Biochem. Characteristics that constitute C4 syndrome – ✓ 2 types of photosynthetic cells ✓ Each vas. bundle is surrounded by a layer of cells – BUNDLE SHEATH CELLS 31 PHOTOSYNTHESIS
- 29. ✓Bundle sheath cells-surrounded by one or more layers of mesophyll cells – this structural specialization – KRANZ ANATOMY ✓Tropical or sub-tropical in origin ✓Better equipped to withstand drought ✓Maintain active photosynthesis under water stress 32 PHOTOSYNTHESIS
- 30. SUB-TYPES NADP-ME TYPE Eg. Zea, Saccharum NAD-ME TYPE Eg. Chloris, Elusine PEP-CK TYPE Eg. Muhlenbergia, Sporobolus 34 PHOTOSYNTHESIS
- 32. MESOPHYLL CELL BUNDLE SHEATH CELL NADP-ME TYPE OAA MALIC ACID PEP PYRUVATE MALATE PYRUVATE 36 PHOTOSYNTHESIS CO2 NADPH NAD P Malate Dehydrogenase CO2 NADPH NADP C3 cycle 2ATP 2ADP Pyruvate P Dikinase NADP -ME PEP-Carboxylase
- 33. MESOPHYLL CELL BUNDLE SHEATH CELL NAD-ME TYPE OAA ASPARTATE PEP PYRUVATE ALANINE ASPARTATE OAA MALATE ALANINE PYRUVATE NADH NAD Malate Dehydrogenase 2ATP 2ADP NAD NADH NAD-ME CO2 CO2 C3 cycle PEP-Carboxylase Transaminase Transaminase Transaminase Transaminase Pyruvate P Dikinase 37 PHOTOSYNTHESIS
- 34. MESOPHYLL CELL BUNDLE SHEATH CELL PEP-CK TYPE OAA ASPARTATE PEP PYRUVATE ALANINE ASPARTATE OAA ALANINE PEP CO2 CO2 Transaminase Transaminase Transaminase ATP ADP 2ATP 2ADP PEP-CK Pyruvate P Dikinase PEP-Carboxylase C3 cycle 38 PHOTOSYNTHESIS
- 35. CAM PATHWAY ➢ Crassulaceae, cactaceae, orchidaceae, bromeliaceae, liliaceae, euphorbiaceae ➢ CAM plants- ➢ Nocturnal stomatal opening ➢ Large vacuoles in chlorophyllous cells ➢ Formation of malic at night, disappears during day time 39 PHOTOSYNTHESIS