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Photosynthesis presentation
The document summarizes key aspects of photosynthesis. It describes: 1) The two main stages of photosynthesis - the light-dependent reactions where light energy is captured to form ATP and NADPH, and the light-independent Calvin cycle where carbon is fixed into sugars. 2) The role of chlorophyll, carotenoids, and other pigments in absorbing light and driving photosynthesis. 3) How the electron transport chain and chemiosmosis are used in the light reactions to generate ATP. 4) The steps of the Calvin cycle including carbon fixation, reduction, and regeneration of RuBP.
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- 1.
- 4. The processwhere by light energy is converted to chemical energy that is store in glucose or other organic compounds. In the presence of light, green plant produce organic compound and oxygen from carbon dioxide and water.
- 5. The overallequation for photosynthesis is: Twelve molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen and six molecules of water. 6CO2 + 12H2O + 18ATP + 12NADPH C6H12O6 + 18ADP + 12NADP+ + 18Pi
- 7. Chlorophyll a The most importance and abundance pigments Absorbs light mainly in the blue-violet and red wavelength Blue green colour Has a methyl (-CH3) side group in porphyrin ring Function to initiate light dependent reaction
- 8. Chlorophyll b Yellowish green in colour Absorbs blue and red wavelength Has an aldehyde (-CHO) side group in porphyrin ring Pass the light energy to chlorophyll a in the reaction center. Helps to increase the range of light a plant can utilize for photosynthesis. Found in green plants and green algae
- 9. Carotenoids Absorbslight maximally in the blue violet region Red, orange or yellow pigments Functions as accessory or antenna pigments Assists by capturing energy from light of wavelength that are not absorb by chlorophyl a and b Protects the chloropyll from oxidation (photoprotection)
- 10. Photosystem Networkof chlorophyll a, b, accessory pigments and associated protein embedded in the thylakoid membrane Functions to channel the excitation energy gathered by any one of its pigments molecule to the reaction centre Passes the energy out of the photosystem for ATP synthesis Consists of : Antenna complex
- 12. Antenna complex Pigments molecule that gathers photon and channel it to the reaction centre Reaction centre Consists of chlorophyll a Pass excited electron to the primary electron acceptor
- 14. Two typesof photosystem: Photosystem I (PSI) / P700 It is called P700 because reaction centre chlorophyll a of a photosystem I absorbs wavelength of 700 nm
- 16. Two typesof photosystem: Photosystem II (PSII) / P680 It is called P680 because reaction centre chloropyll a of a photosystem II absorbs wavelength of 680 nm
- 18. Photosynthesis occursin two main stages: the first stage being towards light dependent reaction the second stage being the light independent reaction (Calvin Benson Cycle) In short the light reactions capture the light energy and utilize it to make high-energy molecule (ATP) ATP are used by the Calvin-Benson Cycle to capture carbon dioxide and make the
- 19. The lightreaction convert solar energy to chemical energy. In the light reaction, light energy absorbed by chlorophyll in the thylakoid drives the transfer of electrons and hydrogen from water to NADP+ (nicotinemide adenine dinucleotide phosphate), forming NADPH. The light reaction also generate ATP by photophosphorylation for the Calvin Cycle.
- 20. Photophosphorylation Photophosphorylation isthe process of creating ATP using a proton gradient created by the energy gathered from sunlight. The process of creating the proton gradient resembles that of the electron transport chain of cellular respiration. But since formation of this proton gradient is light-dependent, the process is called photophosphorylation. Two types of photophosporylation:
- 21. Non-cyclic photophosphorylation Light energy is absorbed by accessory (antenna) pigments of PS II / P680 Then transferred to reaction centre (chlorophyll a) Electron is photoactivated / excited and released This creates an electron deficiency P680 oxidized to P680+ Photolysis of water molecule to form 2 electrons, 2H+ and 1 oxygen atom
- 22. There are2H+ released into the thylakoid lumen The oxygen atom immediately combined with an oxygen atom generated by the splitting of another water molecule forming oxygen molecule (O2) Electron from photolysis of water replace the electrons released from PS II The P680 /PS II molecule returns to its reduced / stabilized state
- 23. The electronsreleased from PS II are accepted by primary electron acceptor/ pheophytin And pass along the ETC; consists of plastoquinone/ Pq, cyctochrome complex, plastocyanin/ Pc and then toP700/ PS I
- 24. As theelectron passed through the cytochrome complex, energy is released through redox reaction. The energy is used to pump H+ from the stroma (low concentration of H+ ) into the thylakoid lumen (high concentration of H+ ) Creating a proton gradient between the stroma and thylakoid lumen that is used in chemiosmosis
- 25. At thesame time, high energy electrons in P700 / PS I are ejected and accepted by primary electron acceptor This creates an electron deficiency P700 oxidized to P700+ PSI functions as electron acceptor, accepting electron from PSII
- 26. The excitedelectron pass along ferredoxin/ Fd NADP+ reductase transfers the electron to NADP+ NADP+ receives proton from photolysis of water to form NADPH (which is released into the stroma) The process also produces oxygen, water and ATP ATP and NADPH produced will be used in the Calvin cycle
- 29. chemiosmosis Production ofATP is by chemiosmosis High concentration of H+ in the thylakoid space Low concentration of H+ in the stroma H+ diffuse from the thylakoid space back into the stroma through ATP synthase The energy release is used to phosphorylate ADP to form ATP (in the stroma) ATP and NADPH produced by non-cyclic photophosphorylation will be used in the
- 30. Cyclic photophosphorylation Involves PSI only No production of NADPH, no release of oxygen Produces ATP Occurs less commonly in plants than noncyclic photophosphorylation, most likely occurring when there is too little NADP+ available.
- 32. Light energyis absorbed by accessory (antenna) pigments of PS I / P700 Then transferred to reaction centre (chlorophyll a) Electron is photoactivated / excited and released Accepted by primary electron acceptor The electron pass to ferredoxin (Fd), cytochrome complex, plastocyanin (Pc) and back to chlorophyll a at the reaction centre PS I / P
- 34. 17.3 LIGHT INDEPENDENT REACTION/CALVINCYCLE A series of reaction lead to the production of NADP+ and ADP and sugar. Occur in stroma of the chloroplast. Input are NADPH, ATP and CO2. First step in carbon fixation which is catalyzed by an enzyme name RuBP carboxylase
- 35. Carbohydrate produceddirectly from the Calvin cycle is actually not glucose but a three carbon sugar named glyceraldehyde- 3-phosphate (G3P). The Calvin cycle involves three phases : Carbon fixation Reduction of PGAL/G3P Regeneration of the CO2 acceptor Ribulose bisphosphate (RuBP)
- 38. I) CARBON FIXATION The Calvin cycle incorporates each CO2 molecule one at the time by attaching it to a five carbon sugar named ribulose biphosphate (RuBP). The enzyme that catalyze this first step is RuBP carboxylase The product of the reaction is a six-carbon intermediately split in half forming two molecules of 3-phosphoglycerate (for each
- 39. II) REDUCTION Eachmolecules of 3-phosphoglycerate receives an additional phosphate from ATP becoming 1,3-biphosphoglycerate A pair of electron donated from NADPH reduces 1,3-biphosphoglycerate to G3P , which store more potential energy. G3P is a sugar ,the same three carbon sugar formed by splitting of glucose (glycolysis)
- 40. Every 3molecules of CO2 that enter the cycle, there are six molecules of G3P formed. But only one molecule of G3P will exit the cycle become the starting material for metabolic pathway that synthesize other organic compound (lipid , amino acid) including glucose and other carbohydrate.
- 41. III) REGENERATION OFTHE CARBON DIOXIDE ACCEPTOR (RuBP) In the complex series of reaction, the carbon skeletons of five molecules of G3P are rearranged by the last step of the Calvin cycle into three molecules of RuBP. To accomplish this, the cycle spend three more molecules of ATP. The RuBP is now prepared to receive CO2 again and the cycle continues. For the net synthesis of one G3P molecule, the Calvin cycle requires a total of nine molecules of ATP, and six molecule
- 42. Plants whichuse only the Calvin cycle for fixing the carbon dioxide from the air are known as C3 plants. About 85% of plant species are C3 plants. They include the cereal grains: wheat, rice, barley, oats. Peanuts, cotton, sugar beets, tobacco, spinach, soybeans, and most trees are C3 plants. C3 plants have the disadvantage that in 17.5 Alternative Mechanism Of Carbon Fixation: Hatch-Slack(C4) And Crassulacean Acid Metabolism (CAM) Pathways
- 43. PHOTORESPIRATION Photorespiration occurswhen the CO2 levels inside a leaf become low. This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss. If the plant continues to attempt to fix CO2 when its stomata are closed, the CO2 will get used up and the O2 ratio in the leaf will increase relative to CO concentrations.
- 44. PG (phosphoglycolate) PGA (glycerate3 phosphate)
- 46. When theCO2 levels inside the leaf drop to around 50 ppm(part per million), RuBP carboxylase starts to combine O2 with RuBP instead of CO2. Photorespiration uses the ATP and NADPH produced in the light reaction. The process result in the loss of fixed carbon dioxide from the plant, reducing photosynthetic efficiency and plant growth.
- 47. Hatch-Slack(C4) pathway C4 plantsuch as sugarcane ,maize and other tropical grasses have evolved a special metabolic adaptation which reduce photorespiration. The metabolic adaptation to reduce photorespiration is Hatch-Slack pathway.
- 48. Comparison between C3and C4 plant leaves C3 plant leaves C4 plant leaves
- 49. C4 plantshave Krantz anatomy // mesophyll cells are arranged concentrically around the bundle sheath cells Plants conduct C4 pathway in the mesophyll cell and Calvin cycle in the bundle sheath cells Use PEP carboxylase to fix CO2 in the mesophyll cells With phosphoenolpyruvate (PEP) forming oxaloacetate (OAA) PEP carboxylase has very a high affinity
- 51. OAA willbe converted to malate Transported to bundle sheath cells Malate converted to pyruvate Releasing CO2 for normal CO2 fixation using Calvin cycle Ensure RuBP carboxylase will be exposed to high CO2 level (reduce photorespiration) Pyruvate transported back to mesophyll cell Converted to PEP (using energy from ATP)
- 52. Crassulacean Acid Metabolism(CAM) Pathway A second strategy to minimize photorespiration is found in succulent plants, cacti, pineapples and several other plant families. Open stomata during the night and close them during the day.
- 53. During thenight, stomata are open. CO2 enters the leaf tissue. CO2 combine with PEP to form oxaloacetate. Oxaloacetate converted into malate. Malate is transported into the vacuole for storage. During the day, stomata are close. Malate is moved into the chloroplasts. Malate converted into pyruvate and