Chapter 10 Photosynthesis

LE 10-2 Plants Unicellular protist Purple sulfur bacteria 10 µm Purple sulfur bacteria 1.5 µm Multicellular algae Cyanobacteria 40 µm

LE 10-3 Leaf cross section Vein Mesophyll Stomata CO2 O2 Mesophyll cell Chloroplast 5 µm Outer membrane Thylakoid Stroma Granum Thylakoid space Intermembrane space Inner membrane 1 µm

LE 10-4 Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2

LE 10-5_1 H2O Light LIGHT REACTIONS Chloroplast

LIGHT REACTIONS ATP NADPH O2 LE 10-5_2 H2O Light LIGHT REACTIONS ATP NADPH Chloroplast O2

H2O CO2 Light NADP+ ADP + CALVIN CYCLE LIGHT REACTIONS ATP NADPH Chloroplast [CH2O] (sugar) O2

Light Reflected light Chloroplast Absorbed Granum light Transmitted

Slit moves to pass light of selected wavelength Green light LE 10-8a White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer 100 The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. Slit moves to pass light of selected wavelength Green light

Slit moves to pass light of selected wavelength LE 10-8b White light Refracting prism Chlorophyll solution Photoelectric tube 100 Slit moves to pass light of selected wavelength The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. Blue light

Absorption of light by chloroplast pigments LE 10-9a Chlorophyll a Chlorophyll b Carotenoids Absorption of light by chloroplast pigments 400 500 600 700 Wavelength of light (nm) Absorption spectra

“head” of molecule; note magnesium atom at center CH3 in chlorophyll a CHO in chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown

Excitation of isolated chlorophyll molecule Fluorescence Excited state e– Heat Energy of electron Photon (fluorescence) Photon Ground state Chlorophyll molecule Excitation of isolated chlorophyll molecule Fluorescence

(INTERIOR OF THYLAKOID) LE 10-12 Thylakoid Photosystem STROMA Photon Light-harvesting complexes Reaction center Primary electron acceptor Thylakoid membrane e– Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)

LE 10-13_1 Primary acceptor e– Energy of electrons Light P680 H2O CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH O2 [CH2O] (sugar) Primary acceptor e– Energy of electrons Light P680 Photosystem II (PS II)

LE 10-13_2 Primary acceptor H2O e– 2 H+ + O2 1/2 Energy of electrons CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH O2 [CH2O] (sugar) Primary acceptor H2O e– 2 H+ + 1/2 O2 e– e– Energy of electrons Light P680 Photosystem II (PS II)

LE 10-13_3 Primary Electron transport chain acceptor Pq H2O e– CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH O2 [CH2O] (sugar) Primary acceptor Electron transport chain Pq H2O e– Cytochrome complex 2 H+ + 1/2 O2 e– Pc e– Energy of electrons Light P680 ATP Photosystem II (PS II)

LE 10-13_4 Primary acceptor Primary Electron transport chain acceptor H2O CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH O2 [CH2O] (sugar) Primary acceptor Primary acceptor Electron transport chain Pq e– H2O e– Cytochrome complex 2 H+ + 1/2 O2 e– Pc e– P700 Energy of electrons Light P680 Light ATP Photosystem I (PS I) Photosystem II (PS II)

LE 10-13_5 ADP Electron Transport chain Primary acceptor Primary H2O CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH O2 Electron Transport chain [CH2O] (sugar) Primary acceptor Primary acceptor Electron transport chain Fd Pq e– e– H2O e– e– NADP+ Cytochrome complex 2 H+ NADP+ reductase + 2 H+ + 1/2 O2 NADPH Pc e– + H+ Energy of electrons e– P700 Light P680 Light ATP Photosystem I (PS I) Photosystem II (PS II)

Electron transport chain Mitochondrion Chloroplast MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE H+ Diffusion Intermembrane space Thylakoid space Electron transport chain Membrane Key ATP synthase Matrix Stroma Higher [H+] Lower [H+] ADP + P i ATP H+

LE 10-17 STROMA (Low H+ concentration) Cytochrome complex H2O CO2 Light NADP+ ADP LIGHT REACTIONS CALVIN CYCLE ATP NADPH STROMA (Low H+ concentration) O2 [CH2O] (sugar) Cytochrome complex Photosystem II Photosystem I Light NADP+ reductase Light 2 H+ Fd NADP+ + 2H+ NADPH + H+ Pq Pc H2O THYLAKOID SPACE (High H+ concentration) 1/2 O2 +2 H+ 2 H+ To Calvin cycle Thylakoid membrane ATP synthase STROMA (Low H+ concentration) ADP + ATP P i H+

Phase 1: Carbon fixation Ribulose bisphosphate LE 10-18_1 H2O CO2 Input Light 3 (Entering one at a time) NADP+ ADP CO2 LIGHT REACTIONS CALVIN CYCLE ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE

RuBisCo Enzyme which fixes carbon from air ribulose bisphosphate carboxylase the most important enzyme in the world! it makes life out of air! definitely the most abundant enzyme It’s not easy being green! I’m green with envy!

LE 10-18_3 Input 3 (Entering one at a time) CO2 H2O CO2 Input Light 3 (Entering one at a time) NADP+ ADP CO2 LIGHT REACTIONS CALVIN CYCLE ATP Phase 1: Carbon fixation NADPH Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 ATP 6 ADP 3 ADP CALVIN CYCLE 3 6 P P ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of the CO2 acceptor (RuBP) 6 NADP+ 6 P i 5 P G3P 6 P Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 1 P G3P (a sugar) Glucose and other organic compounds Output

Adaptations to hot, dry climates: Needles, waxy coatings, not losing leaves in winter, no leaves CAM – close stomates during day - cacti, jade, pineapple C4 –plants in hot regions with intense sunlight – sugarcane, corn. Leaves are modified so p.s. occurs in 2 different types of cells.

LE 10-20 Sugarcane Pineapple C4 CAM CO2 CO2 Mesophyll cell CO2 incorporated into four-carbon organic acids (carbon fixation) Night Organic acid Organic acid Bundle- sheath cell CO2 CO2 Day Organic acids release CO2 to Calvin cycle CALVIN CYCLE CALVIN CYCLE Sugar Sugar Spatial separation of steps Temporal separation of steps

Photosystem II Electron transport chain Photosystem I Light reactions Calvin cycle H2O CO2 Light NADP+ ADP + P i RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP G3P Starch (storage) NADPH Amino acids Fatty acids Chloroplast O2 Sucrose (export)

Photosynthesis summary 1.Where did the energy come from? 2.Where did the electrons come from? 3.Where did the H2O come from? 4.Where did the O2 come from? 5.Where did the O2 go? 6.Where did the H+ come from? 7.Where did the ATP come from? 8.What will the ATP be used for? 9.Where did the NADPH come from? 10.What will the NADPH be used for? Where did the energy come from? The Sun Where did the electrons come from? Chlorophyll Where did the H2O come from? The ground through the roots/xylem Where did the O2 come from? The splitting of water Where did the O2 go? Out stomates to air Where did the H+ come from? The slitting of water Where did the ATP come from? Photosystem 2: Chemiosmosis (H+ gradient) What will the ATP be used for? The work of plant life! Building sugars Where did the NADPH come from? Reduction of NADP (Photosystem 1) What will the NADPH be used for? Calvin cycle / Carbon fixation