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Lecture 3 Outline (Ch. 8) I.Photosynthesis overview A. Purpose B. Location II.The light vs. the “dark” reaction III.Chloroplasts pigments A. Light absorption.

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Presentation on theme: "Lecture 3 Outline (Ch. 8) I.Photosynthesis overview A. Purpose B. Location II.The light vs. the “dark” reaction III.Chloroplasts pigments A. Light absorption."— Presentation transcript:

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

3 Photosynthesis - overview

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

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

6 Photosynthesis – chloroplast recap Outer membrane Inner membrane Thylakoid membrane Stroma Thylakoid space Intermembrane space

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

8 Redox Reactions Equation for photosynthesis 6CO H 2 O + light energy C 6 H 12 O 6 + 6O 2 + 6H 2 O

9 Photosynthesis - overview – thylakoid membrane – thylakoid space – stroma light reactions: dark reactions: Light H2OH2O Chloroplast Light Reactions NADP + P ADP + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)

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

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

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

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

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

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

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

17 Photosynthesis – energy transfer e- from PS II electron transport chain (ETC) PS I  NADPH e- from PS I 2 nd ETC e- carrier: NADP+ e- in PS II, from split H 2 0

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

19 Light reaction - summary inputs: light energy, H 2 O PS II, ETC, PS I, ETC outputs: ATP NADPH O 2 (waste)

20 Self-Check Step of Photosynthesis Location IN chloroplast InputsOutputsATP produced? (don’t need #) e- carriers loaded? Light reaction overall PSII PSI “Dark” reaction overall Know figures of chloroplast reactions/locations!

21 Photosynthesis – energy transfer

22 “Dark” reaction (Light-independent Reaction) 6CO H 2 O + light energy C 6 H 12 O 6 + 6O 2 + 6H 2 O “Dark” reaction: Calvin cycle regenerative anabolic CO 2 in, sugar out during daylight CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvin Cycle G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2OH2O O2O2

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

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

25 Regeneration of C-acceptor multiple steps uses ATP every 3 cycles: 1 G3P made 3 RuBP regenerated #3 – regenerate C-acceptor still 5 G3P  3 RuBP C 3 plants – CO 2 fixed into 3-C 3 stages of Calvin-cycle:

26 Self-Check Step of Photosynthesis Location IN chloroplast InputsOutputsATP produced (don’t need #) e- carriers loaded Light reaction overall PSII PSI “Dark” reaction overall

27 Alternate methods of C fixation

28 CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvin Cycle G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2OH2O O2O2 CO 2 in  stomata open, lose water O 2 fixed – photorespiration – inefficient hot, dry – open stomata less; lowers water loss, lowers CO 2 fix CO 2 into 4-C molecules

29 Photosynthesis – summary light reaction: Light energy + H 2 O light-independent: CO 2, NADPH, ATP O 2, NADPH, ATP Thylakoids G3P (sugar), RuBP Stroma

30 Photosynthesis – summary Where do photosynthetic products go?

31 Photosynthesis – in context of big picture

32 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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