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Photosynthesis final

Photosynthesis presentation

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Photosynthesis final

  1. 1. Photosynthesis It’s not simple being green
  2. 2. Objectives • Understand the difference between autotroph and heterotroph • Describe the location and structure of a chloroplast. Explain how chloroplast structure is related to its function • Recognize and explain the summary equation for photosynthesis • Understand the role of REDOX reactions in photosynthesis • Understand the properties of light discussed in class • Describe the relationship between action and absorption spectrum • Explain what happens when chlorophyll or accessory pigments absorb photons
  3. 3. Objectives continued • List the function and components of a photosystem • Compare cyclic and noncyclic electron flow and explain the relationship between these components of the light reactions • Summarize the light reactions of photosynthesis • Summarize the carbon fixing reactions of the Calvin cycle • Describe the role of NADPH and ATP in the Calvin cycle • Understand why variations of photosynthesis evolved
  4. 4. Overview of Photosynthesis • Process by which chloroplast bearing organisms transform solar light energy into chemical bond energy • 2 metabolic pathways involved • Light reactions: convert solar energy into cellular energy • Calvin Cycle: reduce CO2 to CH2O •Organisms that can perform photosynthesis are called autotrophs whereas those that cannot are called heterotrophs
  5. 5. Photosynthesis Equation • Reduction of carbon dioxide into carbohydrate via the oxidation of energy carriers (ATP, NADPH) • Light reactions energize the carriers • Dark reactions (Calvin Cycle) produce PGAL (phosphoglyceraldehyde) Photosynthesis 6CO2 +6H20 + light → C6H1206 + 6O2
  6. 6. Where is all this happening?
  7. 7. Structure of the Chloroplast • Thylakoid: membranous system within the chloroplast (site of light reactions). Segregates the chloroplast into thylakoid space and stroma. • Grana stacks of thylakoids in a chloroplast • Stroma: region of fluid between the thylakoids and inner membrane where Calvin Cycle occurs
  8. 8. Light • Electromagnetic energy travelling in waves • Wavelength (λ): distance from peak of one wave to the peak of a second wave • inverse relationship between wavelength and energy ↑ λ ↓energy
  9. 9. Visible Spectrum • The portion of the electromagnetic spectrum that our eyes can see • White light contains all λ of the visible spectrum • Colors are the reflection of specific λ within the visible spectrum ∀ λ not reflected are absorbed • Composition of pigments affects their absorption spectrum
  10. 10. Absorption vs. Action • Absorption spectrum is the range of wavelengths that can be absorbed by a pigment • Action spectrum means the wavelengths of light that trigger photosynthesis
  11. 11. Why are plants green? • Pigments contained within the chloroplast absorb most λ of light but absorb the green λ the least • Pigments include – Chlorophyll a – Chlorophyll b – Carotenoids • Carotenes • Xanthophylls
  12. 12. Chlorophyll a • Is only pigment that directly participates in the light reactions • Other pigments add energy to chlorophyll a or dissipate excessive light energy • Absorption of light elevates an electron to a higher energy orbital (increased potential energy)
  13. 13. Photosystems • Collection of pigments and proteins found associated with the thylakoid membrane that harness the energy of an excited electron to do work • Captured energy is transferred between photosystem molecules until it reaches the chlorophyll molecule at the reaction center
  14. 14. What Next? • At the reaction center are 2 molecules – Chlorophyll a – Primary electron acceptor • The reaction-center chlorophyll is oxidized as the excited electron is removed through the reduction of the primary electron acceptor • Photosystem I and II
  15. 15. Electron Flow • Two routes for the path of electrons stored in the primary electron acceptors • Both pathways – begin with the capturing of photon energy – utilize an electron transport chain with cytochromes for chemiosmosis • Noncyclic electron flow – uses both photosystem II and I – electrons from photosystem II are removed and replaced by electrons donated from water – synthesizes ATP and NADPH – electron donation converts water into ½ O2 and 2H+ • Cyclic electron flow – Uses photosystem I only – electrons from photosystem I are recycled – synthesizes ATP only
  16. 16. Noncyclic Electron Flow 1 Electrons at reaction- center are energized 2 H2O split via enzyme catalysed reaction forming 2H+ , 2e- , and 1/2 O2. Electrons move to fill orbital vacated by removed electrons 3,4 Each excited electron is passed along an electron transport chain fueling the chemiosmotic synthesis of ATP
  17. 17. 5 The electrons are now lower in energy and enters photosystem I via plastocyanin (PC) where they are re-energized 6 The electrons are then passed to a different electron transport system that includes the iron containing protein ferridoxin. The enzyme NADP+ reductase assists in the oxidation of ferridoxin and subsequent reduction of NADP+ to NADPH Noncyclic Electron Flow
  18. 18. Non-cyclic Electron Flow
  19. 19. Cyclic Electron Flow • Electrons in Photosystem I is excited and transferred to ferredoxin that shuttles the electron to the cytochrome complex. • The electron then travels down the electron chain and re-enters photosystem I
  20. 20. Where are the photosystems found on the thylakoid membrane?
  21. 21. Chemiosmosis in 2 Organelles • Both the Mitochondria and Chloroplast generate ATP via a proton motive force resulting from an electrochemical inbalance across a membrane • Both utilize an electron transport chain primarily composed of cytochromes to pump H+ across a membrane. • Both use a similar ATP synthase complex • Source of “fuel” for the process differs • Location of the H+ “reservoir” differs
  22. 22. Calvin Cycle • Starts with CO2 and produces Glyceraldehyde 3- phosphate • Three turns of Calvin cycle generates one molecule of product • Three phases to the process – Carbon Fixation – Reduction of CO2 – Regeneration of RuBP
  23. 23. 1 A molecule of CO2 is converted from its inorganic form to an organic molecule (fixation) through the attachment to a 5C sugar (ribulose bisphosphate or RuBP). – Catalysed by the enzyme RuBP carboxylase (Rubisco). • The formed 6C sugar immediately cleaves into 3- phosphoglycerate
  24. 24. 2 Each 3- phosphoglycerate molecule receives an additional phosphate group forming 1,3- Bisphosphoglycerate (ATP phosphorylation) • NADPH is oxidized and the electrons transferred to 1,3- Bisphosphoglycerate cleaving the molecule as it is reduced forming Glyceraldehyde 3- phosphate
  25. 25. 3 The final phase of the cycle is to regenerate RuBP • Glyceraldehyde 3-phosphate is converted to RuBP through a series of reactions that involve the phosphorylation of the molecule by ATP
  26. 26. Variations Anyone? • In hot/arid regions plants may run short of CO2 as a result of water conservation mechanisms • C4 Photosynthesis CO2 may be captured by conversion of PEP (Phosphoenolpyruvate) into oxaloacetate and ultimately malate that is exported to cells where the Calvin cycle is active • CAM Photosynthesis CO2 may be captured as inorganic acids that my liberate CO2 during times of reduced availability
  27. 27. Why are CAM and C4 versions necessary?

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  • JudithSaladaga

    Jul. 27, 2019
  • NilDhasmana

    Dec. 25, 2019

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