Lecture 7 Outline (Ch. 10) 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 VII. Lecture Concepts
Photosynthesis - overview
Photosynthesis - overview Overall purpose: photosynthesis light chemical energy complements respiration - light rxn: solar energy in - dark rxn: energy to organics
Cellular Respiration vs. Photosynthesis Cellular Respiration: (Exergonic) Photosynthesis: (Endergonic)
Photosynthesis chloroplast recap Outer membrane Inner membrane Thylakoid membrane Intermembrane space Stroma Thylakoid space Own DNA Own ribosomes
Photosynthesis - overview Photosynthesis - 1. light rxn: store energy & split water photo NADPH & ATP 2. dark rxn: fix CO 2 & make sugars synthesis Calvin cycle
Redox Reactions 6CO 2 + 12H 2 O + light energy Equation for photosynthesis C 6 H 12 O 6 + 6O 2 + 6H 2 O
light reactions: thylakoid membrane thylakoid space Photosynthesis - overview H 2 O CO 2 dark reactions: stroma Light Light Reactions NADP + ADP + P ATP NADPH Calvin Cycle Chloroplast O 2 [CH 2 O] (sugar)
Photosynthesis light absorption visible light ~380 to 750 nm chloroplast pigments abs blue-violet & red - transmit and reflect green
Photosynthesis light absorption pigments: chlorophyll a -energy-absorbing ring -hydrocarbon tail accessory pigments - chlorophyll b - carotenoids - photoprotective
Photosynthesis light absorption chlorophyll a abs blue-violet, red ~400-500, 650 chlorophyll b & carotenoids abs broadly blue-violet mid-400s more wavelengths used for photosynthesis = more light energy absorbed
Photosynthesis light absorption Pigments have two states: ground & excited chlorophyll abs light e- excited more energy energy transferred
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)
Photosynthesis energy transfer STROMA Light Photosystem II Light Photosystem I THYLAKOID SPACE Thylakoid membrane Photosystem I (PS I) & PS II Difference light wavelength, proteins, where e- from
Photosynthesis energy transfer PSII: absorbs 680 nm, splits water, powerful ETC, ATP made PS I: absorbs 700 nm, e- from PSII, short ETC, NADPH made (less energy)
Photosynthesis energy transfer e- in PS II, from split H 2 0 e- from PS II electron transport chain (ETC) PS I e- from PS I 2 nd ETC e- carrier: NADP+ NADPH
Photosynthesis chemiosmosis How is ATP produced? Chemiosmosis e- down ETC, H+ to thylakoid space H+ conc. gradient H+ down gradient, ATP synthase photophosphorylation
Light reaction - summary inputs: light energy, H 2 O PS II, ETC, PS I, ETC outputs: ATP NADPH O 2 (waste)
Self-Check Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced e- carriers loaded (don t need #) Light reaction overall PSII PSI Dark reaction overall Know figure 10.13, 10.16, 10.17
Light Reaction Review H 2 O CO 2 Light Light Reactions NADP + ADP + P i ATP NADPH Calvin Cycle Chloroplast O 2
Light reaction review 1 / 2 2 H + + O 2 3 H 2 O Primary acceptor 2 e Electron transport chain 4 Cytochrome complex Primary acceptor e Electron transport chain e e 7 8 NADP + reductase NADP + + H + NADPH e e P680 5 P700 Light 1 Light 6 ATP Photosystem II (PS II) Pigment molecules inputs: Energy (light) H 2 O Photosystem I (PS I) outputs: ATP NADPH O 2
Dark reaction (Light-independent Reaction) 6CO 2 + 12H 2 O + light energy C 6 H 12 O 6 + 6O 2 + 6H 2 O Dark reaction: Calvin cycle H 2 O CO 2 regenerative anabolic Light NADP + ADP + P i RuBP 3-Phosphoglycerate Calvin Cycle CO 2 in, sugar out ATP NADPH G3P Starch (storage) during daylight Chloroplast O 2 Sucrose (export)
3 stages of Calvin-cycle: Carbon fixation #1 carbon fixation CO 2 link to 5-C 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco 6-C unstable split 2(3-C) abundant
3 stages of Calvin-cycle: Reduction #2 reduction 3-C reduced e-from NADPH reduced 3-C: G3P
3 stages of Calvin-cycle: #3 regenerate C-acceptor Regeneration of C-acceptor still 5 G3P 3 RuBP multiple steps uses ATP every 3 cycles: 1 G3P made 3 RuBP regenerated C 3 plants CO 2 fixed into 3-C
Alternate methods of C fixation
Alternate methods of C fixation CO 2 in stomata H 2 O CO 2 Light open, lose water NADP + ADP + P i hot, dry open stomata less; lowers water loss, lowers CO 2 Chloroplast ATP NADPH O 2 fixed photorespiration inefficient RuBP 3-Phosphoglycerate Calvin Cycle G3P Starch (storage) O 2 fix CO 2 into 4-C molecules Sucrose (export)
Photosynthesis summary light reaction: Light energy + H 2 O O 2, NADPH, ATP Thylakoids light-independent: CO 2, NADPH, ATP G3P (sugar), RuBP Stroma
Photosynthesis summary Where do photosynthetic products go?
Self-Check Step of Photosynthesis Location IN chloroplast Inputs Outputs ATP produced e- carriers loaded (don t need #) Light reaction overall PSII PSI Dark reaction overall Know figure 10.13, 10.16, 10.17
Lecture 7 Concepts - Describe in words the purpose of photosynthesis - Write the equation for photosynthesis - List the steps of photosynthesis and where they occur - Understand why plants (chloroplasts) appear green - For the light reaction, describe inputs and outputs include what the splitting of water means and the step this is used - Describe the parts of the photosystems and how PSII and PSI are different - Compare photophosphorylation and oxidative phosphorylation - Be able to label on the equation for photosynthesis what is meant by splitting water and where in the chloroplast this takes place - For the Calvin cycle (light independent reaction) describe inputs and outputs include where in the chloroplast this happens - Write out a list of new terminology and provide descriptions