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The summary equation of photosynthesis including the source and fate of the reactants and products. How leaf and chloroplast anatomy relates to photosynthesis. How photosystems convert solar energy to chemical energy. How linear electron flow in the light reactions results in the formation of ATP, NADPH, and O 2. How chemiosmosis generates ATP in the light reactions. How the Calvin Cycle uses the energy molecules of the light reactions to produce G3P. The metabolic adaptations of C 4 and CAM plants to arid, dry regions. 2
Chloroplasts fluid-filled interior chloroplast stroma Thylakoid membrane contains chlorophyll molecules electron transport chain ATP synthase H + gradient built up within thylakoid sac ATP H +H+ H + H + H +H+ H+ H + outer membrane thylakoid granum H +H+ H + thylakoid inner membrane
Plants and other autotrophs are producers of biosphere : use light E to make organic molecules : consume organic molecules from other organisms for E and carbon 4
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: sites of photosynthesis in plants Thylakoid space 6
Sites of Photosynthesis : chloroplasts mainly found in these cells of leaf : pores in leaf (CO 2 enter/o 2 exits) : green pigment in membranes of chloroplasts 7
6CO 2 + 6H 2 O + Light Energy C 6 H 12 O 6 + 6O 2 Reaction: is split transferred with H + to sugar Remember: OILRIG Oxidation: lose e - Reduction: gain e - 8
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis (C.B. van Niel) Reactants: 6 CO 2 12 H 2 O Products: C 6 H 12 O 6 6 H 2 O 6 O 2 9
photo synthesis 10
Nature of sunlight Light = Energy = radiation wavelength (λ): E Visible light - detected by human eye Light: reflected, transmitted or absorbed 11
chloroplast like in cellular respiration proteins in organelle membrane proton (H + ) gradient across inner membrane find the double membrane! ATP synthase enzyme ATP H +H+ H + H + H +H+ H + H + H+ H + H + H +H+ H + H + H +H+ H + H + H+ H + thylakoid H +
ETC of Respiration Mitochondria transfer chemical energy from food molecules into chemical energy of ATP use electron carrier generate H 2 O
ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP use electron carrier generate O 2
photosynthesis respiration sunlight breakdown of C 6 H 12 O 6 H + H + H + H + moves the electrons runs the pump pumps the protons builds the gradient drives the flow of protons through ATP synthase bonds P i to ADP generates the ATP ADP + P i ATP that evolution built H + H + H + H + H +
Chlorophylls & other pigments embedded in thylakoid membrane arranged in a photosystem collection of molecules structure-function relationship How does this molecular structure fit its function?
The spectrum of color V I B G Y O R
Interaction of light with chloroplasts 18
Pigments absorb different λ of light chlorophyll absorb violet-blue/red light, reflect green chlorophyll (blue-green): light reaction, converts solar to chemical E chlorophyll (yellow-green): conveys E to chlorophyll a (yellow, orange): photoprotection, broaden color spectrum for photosynthesis Types: xanthophyll (yellow) & carotenes (orange) (red, purple, blue): photoprotection, antioxidants 19
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1. Which color/wavelength of light provides the MOST energy to plants? 2. Why do most pigments have greater absorbance of shorter wavelengths of light vs. longer wavelengths? 3. Why would a plant not have pigments to capture ALL wavelengths of light? 21
4. Why do most plants appear green? 5. If a plant contained mostly carotenoids, what color would you expect them to appear? 22
Action Spectrum: plots rate of photosynthesis vs. wavelength (absorption of chlorophylls a, b, & carotenoids combined) Engelmann: used bacteria to measure rate of photosynthesis in algae; established action spectrum Which wavelengths of light are most effective in driving photosynthesis? 23
Photosystems of photosynthesis 2 photosystems in thylakoid membrane collections of chlorophyll molecules act as light-gathering molecules P 680 = absorbs 680nm wavelength red light P 700 = absorbs 700nm wavelength red light reaction center antenna pigments
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Summary: 1. Light energy splits to releasing high energy electrons (e - ) 2. Movement of e - used to generate 3. Electrons end up on NADP +, reducing it to 26
Electrons in chlorophyll molecules are excited by absorption of light 27
Photosystem: reaction center & light-harvesting complexes ( + ) 28
Two routes for electron flow: A. (noncyclic) electron flow B. electron flow 29
1. Chlorophyll excited by light absorption 2. E passed to reaction center of (protein + chlorophyll ) 3. e - captured by Redox reaction e - transfer e- prevented from losing E (drop to ground state) 4. is split to replace e - formed 30
5. e - passed to via 6. E transfer pumps to thylakoid space 7. produced by 8. e - moves from PS I s primary electron acceptor to 2 nd ETC 9. NADP + reduced to NADPH 31
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Mechanical analogy for the light reactions 33
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Proton motive force generated by: (1) H + from water (2) H + pumped across by cytochrome (3) Removal of H + from stroma when NADP + is reduced 36
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Occurs in the Uses,, Produces 3-C sugar (glyceraldehyde-3-phosphate) Three phases: 1. fixation 2. Reduction 3. Regeneration of (CO 2 acceptor) 38
Phase 1: 3 CO 2 + (5-C sugar ribulose bisphosphate) Catalyzed by enzyme (RuBP carboxylase) 39
Phase 2: Use and to produce 1 net 40
Phase 3: Use to regenerate 41
Alternative mechanisms of carbon fixation have evolved in hot, arid climates Problem for C 3 plants Hot or dry days gain H 2 O = stomates open lose H 2 O = stomates close adaptation to living on land, but creates PROBLEMS! 42
When stomates close Closed stomates lead to build up from light reactions is depleted in Calvin cycle causes problems in Calvin Cycle O 2 xylem (water) CO 2 phloem (sugars) O 2 CO 2 H 2 O 43
Alternative mechanisms of carbon fixation have evolved in hot, arid climates Photorespiration Metabolic pathway which: Uses & produces Uses ATP No production (rubisco binds breakdown of RuBP) Occurs on hot, dry bright days when stomata close (conserve H 2 O) Why? Early atmosphere: low O 2, high CO 2? 44
Evolutionary Adaptations 1. Problem with C 3 Plants: CO 2 fixed to 3-C compound in Calvin cycle Ex. Rice, wheat, soybeans Hot, dry days:» partially close stomata, CO 2» Photorespiration» photosynthetic output (no sugars made) 45
Evolutionary Adaptations 2. C 4 Plants: CO 2 fixed to 4-C compound Ex. corn, sugarcane, grass Hot, dry days stomata close 2 cell types = & cells» mesophyll : fixes CO 2 (4-C), pump CO 2 to bundle sheath» bundle sheath: CO 2 used in Calvin cycle 2 stages of photosynthesis are separated photorespiration, sugar production 46
C 4 Leaf Anatomy 47
3. CAM Plants: Crassulacean acid metabolism (CAM) NIGHT: stomata open CO 2 enters converts to, stored in cells DAY: stomata light reactions supply ATP, NADPH; CO 2 released from organic acids for Calvin cycle Ex. cacti, pineapples, succulent (H 2 O-storing) plants 2 stages of photosynthesis are separated 48
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C 3 C 4 CAM C fixation & Calvin together C fixation & Calvin in different C fixation & Calvin at different Rubisco PEP carboxylase Organic acid 51
Plant: Global: for respiration Cellulose Production source 52
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Light ENERGY organic molecules released stored in Photosynthesis split Light Reaction ATP energized electrons using involves both in which Reduce NADP+ to regenerate Calvin Cycle fixed to RuBP C 3 phosphorylated and reduced G3P to form in process called photophosphorylation & other carbs 55
RESPIRATION Plants + Animals Needs O 2 and food Produces CO 2, H 2 O and ATP, NADH Occurs in mitochondria membrane & matrix Oxidative phosphorylation Proton gradient across membrane PHOTOSYNTHESIS Plants Needs CO 2, H 2 O, sunlight Produces glucose, O 2 and ATP, NADPH Occurs in chloroplast thylakoid membrane & stroma Photorespiration Proton gradient across membrane 56
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