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Lecture 3 Outline (Ch. 8)

Lecture 3 Outline (Ch. 8). Photosynthesis overview A. Purpose B. Location The light vs. the “dark” reaction Chloroplasts pigments A. Light absorption B. Types Light reactions A. Photosystems B. Photophosphorylation V. The light independent reaction (“dark” reaction)

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Lecture 3 Outline (Ch. 8)

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  1. Lecture 3 Outline (Ch. 8) • Photosynthesis overview • A. Purpose • B. Location • The light vs. the “dark” reaction • Chloroplasts pigments • A. Light absorption • B. Types • Light reactions • A. Photosystems • B. Photophosphorylation • V. The light independent reaction (“dark” reaction) • A. Carbon “fixation” • B. Reduction • C. Regeneration • VI. Alternative plants

  2. Photosynthesis - overview

  3. Photosynthesis - overview Overall purpose: • photosynthesis – light chemical energy • complements respiration Energy for all life on earth ultimately comes from photosynthesis

  4. Cellular Respiration: (Exergonic) Photosynthesis: (Endergonic) Cellular Respiration vs. Photosynthesis

  5. Photosynthesis – chloroplast recap Outer membrane Inner membrane Thylakoid membrane Stroma Thylakoid space Intermembrane space

  6. Photosynthesis - overview • Photosynthesis - 1. light rxn: store energy & split water – “photo” NADPH & ATP 2. dark rxn: “fix” CO2 & make sugars – “synthesis” Calvin cycle

  7. 6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O Redox Reactions Equation for photosynthesis

  8. CO2 H2O Light NADP+ ADP + P Calvin Cycle Light Reactions ATP NADPH Chloroplast [CH2O] (sugar) O2 Photosynthesis - overview • light reactions: • dark reactions: – thylakoid membrane – stroma – thylakoid space

  9. Photosynthesis – light absorption • visible light ~380 to 750 nm • chloroplast pigments – abs blue-violet & red - transmit and reflect green

  10. Photosynthesis – light absorption • pigments: • chlorophyll a -energy-absorbing ring -hydrocarbon tail • accessory pigments - chlorophyll b - carotenoids - photoprotective

  11. Photosynthesis – light absorption • chlorophyll a – abs blue-violet, red 400-450, 650-700 nm • chlorophyll b & carotenoids – abs broadly blue-violet mid-400s • more wavelengths used for photosynthesis = more light energy absorbed

  12. Photosynthesis – light absorption Pigments have two states: ground & excited • chlorophyll abs light • e- excited • more energy • energy transferred

  13. Photosynthesis – light absorption Pigments are held by proteins in the thylakoid membranes light harvesting complex • energy absorbed from light - to pigments • to reaction center - two special chlorophyll a - proteins - 1° electron acceptor • light harvesting complex & reaction center = photosystem (PS)

  14. STROMA Photosystem I Photosystem II Light Light THYLAKOID SPACE Thylakoid membrane Photosynthesis – energy transfer • Photosystem I (PS I) & PS II • Difference – light wavelength, proteins,  where e- from

  15. Photosynthesis – energy transfer • PSII: absorbs 680 nm, splits water, powerful ETC, ATP made • PS I: absorbs 700 nm, (less energy) e- from PSII, short ETC, NADPH made

  16. • e- from PS II electron transport chain (ETC) PS I • e- from PS I 2nd ETC e- carrier: NADP+ Photosynthesis – energy transfer • e- in PS II, from split H20  NADPH

  17. Photosynthesis – chemiosmosis • How is ATP produced? Chemiosmosis • e- down ETC, H+ to thylakoid space • H+ conc. gradient • H+ down gradient, ATP synthase photophosphorylation

  18. Light reaction - summary • inputs: light energy, H2O • PS II, ETC, PS I, ETC • outputs: ATP NADPH O2 (waste)

  19. Self-Check Know figures of chloroplast reactions/locations! 

  20. Photosynthesis – energy transfer

  21. H2O CO2 Light NADP+ 6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O ADP P + i RuBP 3-Phosphoglycerate Calvin Cycle ATP G3P Starch (storage) NADPH Chloroplast O2 Sucrose (export) “Dark” reaction (Light-independent Reaction) • “Dark” reaction: Calvin cycle • regenerative • anabolic • CO2 in, sugar out • during daylight

  22. Carbon fixation • 3 stages of Calvin-cycle: • #1 – carbon fixation • CO2 link to 5-C • 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco abundant • 6-C unstable – split  2(3-C)

  23. Reduction • 3 stages of Calvin-cycle: • #2 – reduction • 3-C reduced • e- from NADPH • reduced 3-C: G3P

  24. Regeneration of C-acceptor • 3 stages of Calvin-cycle: • #3 – regenerate C-acceptor • still 5 G3P  3 RuBP • multiple steps • uses ATP • every 3 cycles: 1 G3P made 3 RuBP regenerated • C3 plants – CO2 fixed into 3-C

  25. Self-Check

  26. Alternate methods of C fixation

  27. H2O CO2 Light NADP+ ADP P + i RuBP 3-Phosphoglycerate Calvin Cycle ATP G3P Starch (storage) NADPH Chloroplast O2 Sucrose (export) Alternate methods of C fixation • CO2 in  stomata • open, lose water • hot, dry – open stomata less; lowers water loss, lowers CO2 • O2 fixed – photorespiration – inefficient • fix CO2 into 4-C molecules

  28. Photosynthesis – summary • light reaction: Light energy + H2O O2, NADPH, ATP Thylakoids • light-independent: CO2, NADPH, ATP G3P (sugar), RuBP Stroma

  29. Photosynthesis – summary Where do photosynthetic products go?

  30. Photosynthesis – in context of big picture

  31. Lecture 3 Summary • 1. Photosynthesis Overview (Ch. 8) • Purpose • Redox reactions • Electron carriers & sugars • 2. Light (Ch. 8) • Absorption pigments • Light spectra/wavelengths • 3. Locations of steps, inputs/outputs, purpose, description (Ch. 8) • PSI vs. PS II • Whole light reaction [includes chemiosmosis] • “dark” reaction/Calvin cycle [3 steps] • 4. Alternate modes of photosynthesis (Ch. 8) • 5. Photosynthesis context (Ch. 8) • - Uses for products • - Relationship of cell respiration and photosynthesis

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