Lecture 12: Photosynthesis • Chapter 10, pp. 185-203 • Homework (WebCT), due next Monday, Feb. 7, before 12PM (noon), based in part on independent reading of Ch. 10 • Today’s office hour is canceled. Instead, I’ll hold an office hour on Friday, 1-2PM, Espresso Roma (Price Center)Overview: The Process That Feeds the Biosphere Autotrophs (producers): produce their organic molecules from CO2 and raw inorganic materials Photosynthetic organisms are called photoautotrophs Heterotrophs (consumers): consume autorophs and other heterotrophs to obtain basic organic moleculesFig.%10(2!(a)%Plants%(c)%Unicellular%%pro9st%10!µm!1.5!µm!40!µm!(d)%Cyanobacteria%(e)%Purple%sulfur%%%%%%%bacteria%(b)%Mul9cellular%alga%Photosynthesis: the process in which the energy of sunlight is used to make organic molecules from H2O and CO2 Directly or indirectly, photosynthesis nourishes almost the entire living world Examples of photoautotrophs:Fig. 10-3a 5 µm Mesophyll cell Stomata!CO2 O2 Chloroplast Mesophyll!Vein!Leaf cross section!Photosynthesis is carried out in the mesophyll cells of the leavesFig.%10(3b!1!µm!Thylakoid!space!Chloroplast!Granum!Intermembrane!space!Inner!membrane!Outer!membrane!Stroma!Thylakoid!Chloroplast – the photosynthetic organelle• Photosynthesis can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O 6 CO2 12 H2O 6 O2 6 H2O C6H12O6Photosynthetic Reactions 1. Light Reaction: – Solar energy is captured in energized electrons – Electrons move down electron transport chain • Pumps H+ into thylakoids • Used to make ATP out of ADP and NADPH out of NADP 2. Calvin Cycle (dark) Reaction – CO2 is reduced to a carbohydrate – Reduction requires the ATP and NADPH produced aboveLight!Fig.%10(5(2!H2O!Chloroplast!Light!ReacEons!NADP+!P!ADP!i!+!ATP!NADPH!O2!Light!Fig.%10(5(4!H2O!Chloroplast!Light!ReacEons!NADP+!P!ADP!i!+!ATP!NADPH!O2!Calvin!Cycle!CO2![CH2O]!(sugar)!Fig. 10-11 Heat Excited state Photon Ground state Photon Energy of electron e– Chlorophyll molecule Fig.%10(10!Porphyrin!ring:!lightQabsorbing!“head”!of!molecule!in!chlorophyll!a!CH3!Hydrocarbon!tail:!interacts!with!hydrophobic!regions!of!proteins!inside!thylakoid!membranes!of!chloroplasts!CHO!in!chlorophyll!b!The Light reaction: Chlorophyll is a pigment that absorbs lightFig.%10(12!THYLAKOID!SPACE!(INTERIOR!OF!THYLAKOID)!STROMA!e–!Pigment!molecules!Photon!Transfer!of!energy!Special!pair!of!chlorophyll!a#molecules!Thylakoid!membrane!Photosystem!Primary!electron!acceptor!ReacEonQcenter!complex!LightQharvesEng!complexes!Photosystem a complex of pigments and proteins that captures light energy and harvests it in the form of high-energy electrons Two types of Photosystems work together: Photosystem II Photosystem IFig.%10(14!Mill!makes!ATP!e–#NADPH!Photon!e–#e–#e–#e–#e–#Photon!ATP!Photosystem!II! Photosystem!I!e–#A mechanical analogy for the light reaction. Main goal: generation of ATP and NADPHPigment!molecules!Light!P680!e–#Primary!acceptor!2!1!e–#e–!2!H+!O2!+!3!H2O!1/2!4!Pq!Pc!Cytochrome!complex!5!ATP!Photosystem!I!(PS!I)!Light!Primary!acceptor!e–#P700!6!Fd!NADP+!reductase!NADP+!+!H+!NADPH!8!7!e–#e–#6!Fig.%10(13(5!Photosystem!II!(PS!II)!Fig. 10-17 Light Fd Cytochrome complex ADP + i H+ ATP P ATP synthase To Calvin Cycle STROMA (low H+ concentration) Thylakoid membrane THYLAKOID SPACE (high H+ concentration) STROMA (low H+ concentration) Photosystem II Photosystem I 4 H+ 4 H+ Pq Pc Light NADP+ reductase NADP+ + H+ NADPH +2 H+ H2O O2 e– e– 1/2 1 2 3Clicker question 12-2 Which of the following is NOT common between Cellular Respiration in mitochondria and Photosynthesis in chloroplasts? A) Chemiosmotic coupling B) Generation of proton gradient C) Electron Transport Chain D) NADH as electron donorsThe Calvin Cycle - Takes place in the stroma – CO2 is reduced to a carbohydrate – Reduction requires the ATP and NADPH produced in the Light reactionFig. 10-18-3 Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO2 P 3 6 3 3 P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P 6 6 6 NADP+ NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle 3 3 ADP ATP 5 P Phase 3: Regeneration of the CO2 acceptor (RuBP) G3PImportance of Calvin Cycle • G3P (glyceraldehyde-3-phosphate) can be converted to many other molecules • The hydrocarbon skeleton of G3P can form – Fatty acids and glycerol to make plant oils – Glucose phosphate (simple sugar) – Fructose (which with glucose = sucrose) – Starch and cellulose – Amino acidsa.____ c.____ d.____ b.____ e.____ f.____ h.____ g.____ Label the following diagram using these labels: water, G3P, carbon dioxide, oxygen, ATP, ADP + P, NADPH, and