Todays topics: of various • Finish molecules • Leaves and

• How light energy is captured – light reactions produce ATP and NADPH – Photosystems 1 and 2 The arrows go both directions • How sugars are made – “dark” reactions reduce CO2 to sugars Oct 11, 2021 – Calvin cycle 1

Glucose AMP Photosynthesis H O The control of 2 CO2 Fructose-6-phosphate Stimulates + cellular Phosphofructokinase – – Light energy Fructose-1,6-bisphosphate respiration Inhibits Inhibits NADP+

ADP + LIGHT P i CALVIN Pyruvate REACTIONS CYCLE

ATP Citrate ATP Acetyl CoA Stroma NADPH

Citric acid cycle

O2 [CH2O] (sugar) Oxidative phosphorylation

Figure 9.2 Chloroplast Mesophyll Cell Light Leaf cross section energy Vein Chloroplast

ECOSYSTEM Mesophyll

Photosynthesis 5 µm

in CO2 O CO + H O Organic Stomata 2 2 2 molecules+ O2 Cellular respiration in mitochondria

Outer membrane

Thylakoid Intermembrane space

Stroma Inner ATP powers membrane ATP most cellular work

Heat energy 6

1 µm

1 Chlorophyll molecules are embedded in the thylakoid membrane

Light Reactions (energy capture)

Dark Reactions (energy utilization) 8

Pigments Absorption Spectra of Antenna Reflected Pigments absorb certain Light Light wavelengths of Chlorophyll a light Chlorophyll b Chloroplast

Carotenoids chloroplast pigments pigments chloroplast Absorption of light by light of Absorption

Absorbed Granum

light Figure 10.9 Transmitted light 9 Wavelength of light (nm) 10

Excited – Capture e state

• Reaction Center Chlorophyll electron boosted to high energy x level Heat • e- transferred to Energy of election an electron x Photon transport chain () • need Ground replacement state Photon Chlorophyll electron molecule

11 12

2 STROMA Photosystem II Photosystem II Reaction STROMA Light 2 H+ Light center

Fd

Antenna Photon

pigments e– Pq Pc Thylakoid membrane

H2O 1⁄ O THYLAKOID 2 2 e- SPACE 2 H+ 2 H+ THYLAKOID SPACE H2O – O2 Water Splitting Complex 13 14

STROMA Linear Electron Flow Photosystem II Photosystem I Photosystem II Photosystem I Light 2 H+ Light - Light Energy used to - Light Energy used Form H+ gradient to reduce NADPH Fd (ATP Synthesis)

e ATP – Pq e e Pc – – NADPH e – e e – H2O – 1 THYLAKOID ⁄2 O2 SPACE 2 H+ 2 H+ e –

16 15 Photosystem II Photosystem I

H2O CO2 LIGHT NADP+ Cyclic Electron Flow ADP CALVIN LIGHT Light CYCLE REACTOR ATP Photosystem I can also Dependent NADPH + e– make H gradient by ATP Reactions O STROMA 2 [CH2O] (sugar) itself. (Low H+ concentration) Cytochrome Produce Photosystem II complex Photosystem I + e– e– Light NADP reductase + 2 H 3 Fd NADP+ + 2H+ NADPH NADPH e– NADPH + H+ e– Pq e– And Pc 2

H2O 1 ⁄2 O Mill ATP 2 THYLAKOID SPACE 1 + +2 H+ 2 H makes (High H+ concentration)

ATP Photon Photon To To power Calvin cycle e– The

Calvin ATP Thylakoid synthase membrane Photon Cycle STROMA ADP (Low H+ concentration) ATP P 17 + Photosystem II Photosystem I H 18

3

H O CO 2 2 The Dark Reactions Light NADP+ • The Calvin Cycle (C3) ADP – Reduce CO2 à Sugars CALVIN – Requires ATP and NADPH LIGHT CYCLE from light reactions REACTIONS ATP

NADPH

O2 [CH2O] (sugar) 20

“RUBISCO” is Phase 1: H2O CO2 theLight Input NADP+ 3 (Entering one ADP CO at a time) Carbon 2 LIGHT CALVIN that REACTIONSfixes CYCLE ATP 1: Carbon NADPH fixation carbon dioxide fixation Rubisco O 2 [CH2O] (sugar) 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate 3-Phosphoglycerate (RuBP) 6 ATP 6 ADP

3 ADP CALVIN CYCLE 6 P P 3 ATP 1,3-Bisphosphoglycerate

6 NADPH

6 NADP+

6 P Phase 3: i 5 P G3P 6 P Regeneration of Glyceraldehyde-3-phosphate 2: (G3P) the CO acceptor ReductionPhase 2: 2 Reduction (RuBP) 1 P G3P Glucose and (a sugar) other organic Output compounds 21

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