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Photosynthesis

Photosynthesis. Light energy (kinetic) converted into chemical energy (potential) Anabolic, endergonic 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Light (chlorophyll + accessory pigments) Light = electromagnetic radiation; waves. Photosynthesis. CO 2 and H 2 O are ‘energy-poor’

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Photosynthesis

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  1. Photosynthesis • Light energy (kinetic) converted into chemical energy (potential) • Anabolic, endergonic • 6CO2 + 6H2O C6H12O6 + 6O2 Light(chlorophyll + accessory pigments) • Light= electromagneticradiation; waves

  2. Photosynthesis • CO2 and H2O are ‘energy-poor’ • Become energy-rich; C-H bond • CO2 is reduced; H2O is oxidized • CO2 + H2 CH2O (glucose) + O2

  3. Autotroph; Photoautotroph – plants, algae Chemoautotroph – Bacteria Heterotroph Photoheterotroph Bacteria Chemoheterotroph Animals, Fungi 2 Ways Organisms Get Energy

  4. Photosynthesis • 2 step process: • ‘Light reactions’; water is split, ATP generated, H gathered • Calvin Cycle; CO2 incorporated into other organic molecules; (‘carbon fixation’)

  5. Leaves • Chlorophyll= 1o pigment • Most chloroplasts are in the Mesophyll of leaf • Stomata = pores in leaf (?) • Vascular bundles • Transport water and glucose

  6. Chloroplasts • Divided into 3 areas: 1. Intermembrane space 2. Thylakoid = membrane folded into flattened discs; cristae 3. Stroma = viscous fluid around grana (stacks of thylakoids); matrix

  7. Light reactions in thylakoid membrane, and thylakoid space (lumen) Calvin cycle instroma

  8. Nanometers; nm The Nature of Light • Sun produces electromagnetic energy by fusion of H • Quantum mechanics; duality of light • Wave-like; frequency, wavelength • Particle-like; photons

  9. Light • White light ‘split’ by diffraction gradient (prism); ‘bent’ • Longer wavelengths = less energy; refracted more • Shorter wavelengths = more energy; refracted less • Spectrum

  10. Light • Spectrophotometer • Measures light transmittance/absorption at adjustable frequencies • ? Wavelengths are absorbed • Absorbed waves are ‘useable’ • ‘Green’ is reflected; Green must not be used

  11. Spectrophotometer

  12. Use of light in Photosynthesis • Engelmann, 1883. (science) • Used prism to expose algae to various wavelengths • Measured growth of aerobic bacteria (?) • Measured rate of photosynthesis by measuring the appearance of O2

  13. Process of Science • Action spectrum (how much photosynthesis is occurring) does not match absorption spectrum (what wavelengths are being absorbed) • Absorption is also occurring between ‘blue’ and ‘red’ • What is going on? • Must be more pigments than chlorophyll(s)

  14. Pigments • Chlorophyll a; b • C – G • Accessory pigments; • Carotenoids - yellows, oranges, reds • Keep chlorophyll from ODing

  15. Pigment = molecule that has color

  16. Overview of Photosynthesis • Light reactions: membrane-bound proteins • Noncyclic photophosphorylation • Chemiosmosis • Cyclic photophosphorylation • Calvin cycle – chemical ‘soup’

  17. Light Reactions • Production of ATP • Capture of H+ • Formation of O2

  18. Photoexcitation of Chlorophyll e_ Heat Photon Fluorescence: dinoflagellates e_ Chlorophyll

  19. Photoexcitation of Chlorophyll • Photosystem = cluster of pigment molecules • Chlorophyll a, b, and accessory pigments • Most pigment molecules are ‘antennae’ • Pass excited energy to one chlorophyll a • Reaction center - chlorophyll molecule

  20. Electron not allowed to drop back to ground state photosystem

  21. 2 Types of Photosystems • Named in order of discovery • Photosystem I; 700 nm (red) • Photosystem II: 680 nm (red) • Photosystem II is ‘beginning’

  22. e- isexcited to a higher level of energy; picked up by electron acceptor

  23. Photosystem II • PS II receives light photons (from sun) • Electrons from chlorophyll become ‘excited’ • Excited electrons picked up by 1o acceptor molecule • Excited electrons passed down ETC to PS I (series of cytochromes)

  24. Enzyme splits water releasing e-and oxygen; e- goes to P680 replacing one lost from the photon

  25. Photosystem II • Chemiosmotic generation of ATP • Photophosphorylation • Electrons from water are extracted and donated back to PS II (cycle) • Water splits into H2 + O2 (waste)

  26. e- passed down an ETC; generates ATP; by chemiosmosis

  27. e- travelsETCtoPhotosystemI;P700boostse-toitsprimaryacceptor

  28. e- passed from I down ETC to NADP; NADPH goes to Calvin

  29. 1o Acceptor 2 e_ 2 e_ H2O Chemiosmosis 2 e_ 2 e_ O2 2 e_ H+ Photosystem II P680 Reaction center

  30. Photosystem I 1o Acceptor 2 e_ Fd 2 e_ NADP+ 2 e_ e from PS II NADP+ reductase H+ NADPH To Calvin

  31. Cyclic photophosphorylation

  32. Melvin Calvin • Used tracers to determine carbon fixation and the sequence of events • Lab next to atomic reactor • Also used H2 to discover that water is the source of H

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