Lecture 5- Photosynthesis PDF

photons isource of energy ~ Photosynthesis 7 of carbohydrates Prof. Dr. Gerhard Grüber Nanyang Technological University School of Biological Sci...

photons isource of energy ~ Photosynthesis 7 of carbohydrates Prof. Dr. Gerhard Grüber Nanyang Technological University School of Biological Sciences [email protected]  Concept of the electron transport chain H2 + 1/2 O2 2H + /2 O2 1 Controlled 2 H+ + 2 e− release of energy provide stepwise ATP Free energy, G Free energy, G release of energy ATP Explosive release ATP 2 e− 1/ 2 O2 2 H+ H2O H2O (a) Uncontrolled reaction (b) Cellular respiration © 2017 Pearson Education, Ltd  Concept of the electron transport chain NADH (least electronegative) 50 2 e− NAD+ FADH2 Free energy (G) relative to O2 (kcal/mol) 2 e− Complexes I-IV FAD I 40 FMN Fe S II Fe S Q III Cyt b Fe S 30 Cyt c1 IV Cyt c Cyt a Electron transport Cyt a3 20 chain 2 e− 10 2 H+ + ½ O 2 final e-acceptor 0 (most electronegative) © 2017 Pearson Education, Ltd H2O  The respiratory chain for oxidative phosphorylation depwise e-trsf H+ Patie force H+ ATP H+ synthase H+ Protein complex Cyt c of electron carriers IV Q I III II 2 H+ + ½ O2 H 2O FADH2 FAD NADH NAD+ ADP + P i ATP (carrying electrons from food) H+ Electron transport chain Chemiosmosis Oxidative phosphorylation © 2017 Pearson Education, Ltd  The role of photosynthesis in metabolism lanabolic process Questions of today’s lecture: What are the general properties of photosynthesis? molecules that able to absorb light ~ form How is solar energy captured by chlorophyl? carbohydrate What kinds of photosystems are used to capture light energy? end pdt How does light drive the synthesis of ATP? fromTo of Sugar How is carbon dioxide used to make organic molecules? L like > used here carbohydrates w photosynthesis by-pot : On Mathews, van Holde, Ahern: Biochemistry 3rd edition  Global photosynthesis absorb Light ⚫ Essentially all free energy needed energy to drive all biological reactions on earth is trapped from solar energy ECOSYSTEM by the process of photosynthesis. – How much carbon is reduced to carbohydrate by Photosynthesis photosynthesis per year? in chloroplasts – How much solar energy is polts : stored? Organic CO2 + H2O + O2 molecules – How much energy is this as compared to the total solar Cellular respiration energy received by the earth? in mitochondria – Does that raise any question in your mind regarding world food production its scope and limitations? ⚫ It is estimated that 1011 tons of carbon is assimilated into organic ATP powers ATP matter annually by photosynthesis, most cellular work and the amount of free energy stored for this is 1.5 x 1022 kJ. Heat energy © 2017 Pearson Education, Ltd  Location of photosynthesis in the plant Leaf cross section Chloroplasts Vein Mesophyll Stomata CO O 2 2 Chloroplast Mesophyll cell Outer membrane Thylakoid Thylakoid Intermembrane stack of 20 mm Stroma Granum space space thylakoids grava (plural) Inner in chloroplast membrane © 2017 Pearson Education, Ltd Chloroplast 1 mm  Photosynthesis consists of both light- and dark reactions If a chloroplast suspension is illuminated in the absence of CO2, oxygen is evolved. If the illuminated chloroplasts are now placed in the dark and supplied with CO2, net hexose synthesis can be observed. Thus the evolution of oxygen can be temporally separated from CO2 fixation and also has a light dependency that CO2 fixation lacks. The light reactions of photosynthesis are associated with the thylakoid membranes, whereby the dark reactions (CO2 fixation) are located in the stroma. Garett & Grisham: Biochemistry 4th edition  An overview of photosynthesis Light H2O putsfromcatabolises CO2 enter as substrate into thylkoids NADP+ rat ADP + ~ LIGHT Pi CALVIN REACTIONS CYCLE ATP Thylakoid Stroma provided energy NADPH phosphorylated on eC-atom of ribose of NAD molecule Chloroplast MADPH mostly used in biosynthesis O2 processes [CH2O] (sugar) © 2017 Pearson Education, Ltd  The two subprocesses of photosynthesis ⚫ The overall process (CO2 + H2O → [C H2O] + O2) occurs in two phases: energy from ⚫ Light reactions: ~ photons – H2O + NADP+ + ADP + Pi + n(h·ν) → O2 + ATP + NADPH Go of – Consider the energetics aspects of this reaction. · photons ⚫ Dark reactions: – CO2 + NADPH + ATP → [C H2O] + NADP+ + ADP + Pi ⚫ The light reactions of photosynthesis generate energy rich NADPH and ATP at the expense of solar energy. These products are used in the carbon assimilation reactions, which occur in light or darkness, to reduce CO2 to form trioses and more complex compounds (such as glucose) derived from trioses. Campbell: Biology in Focus 2nd edition  Basic chemical reactions ⚫ Overall photosynthetic reaction is an oxidation-reduction reaction: – CO2 + H2O → [CH2O] + O2 This is oxygenic photosynthesis. – CO2 is reduced and H2O is oxidized. The O2 is evolved as by-product ⚫ Where does the O2 come from? Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2 ⚫ In anoxygenic photosynthesis, H2O is not the reductant. In green sulfur bacteria: – CO2 + H2S → [C H2O] + S, hydrogen sulfide is the reductant.  Examples of oxygenic and anoxygenic photosynthesis itself oxidised - Organisms Reductant Reaction Plants, algae, Cyanobacteria H2O CO2 + 2H2O → [C H2O] + H2O + O2 Sulfur bacteria H2S, S CO2 + 2H2S → [C H2O] + H2O + 2S [0) D Non-sulfur bacteria H2 or CO2 + 2 Lactate → [C H2O] + H2O + 2 Pyr organic molecules Anoxygenic photosyntesis began about 3.5 billion years ago when the atmosphere lacked O2. Oxygenic photosynthesis evolved about 2 billion years ago.  Basic energetics of photosynthesis ⚫ How much free energy is required to reduce 1 mole of CO2? ⚫ Standard ∆G of glucose oxidation to CO2 is -2870 kJ/mol glucose. & divide 6 C6H12O6 → 6 CO2 + 6 H2O by & strate of photosynthesis ⚫ So, standard ∆G is required to reduce 1 mol CO2 is + 480 kJ. every proud by photons ⚫ In photosynthesis, the source of this energy is light. Considering this requirement, the basic reaction should be: CO2 + 2 H2O + n photons → [C H2O] + H2O + O2 Where n is the number of moles of photon required to reduce one mole of CO2 into carbohydrate. Remember: H2O is a poor donor of electrons (E°’ = 0.815 V). Therefore light is required to create a good electron donor.  The spectrum of electromagnetic radiation far UV far infrared shorter wavelength have more energy The energy, E, in a “mole” of photons of visible light is 170 to 300 KJ. These amounts of energy are almost an order of magnitude greater than the 30 to 50 KJ required to synthesize a mole of ATP from ADP and Pi. Visible light is : perfect provider of energy in e frm of photons D. L. Nelson, M. & M. Cox, Lehninger Principles of Biochemistry, 4th edition  Why leaves are green: interaction of light with chloroplasts Light mostwavelength of light is Reflected light Chloroplast Absorbed Granum light Transmitted green light © 2017 Pearson Education, Ltd  White Refracting Chlorophyll Photoelectric light prism solution tube Galvanometer high amt of (green) a is light transmitted light transmitted Slit moves to Green pass light light of selected wavelength. only a little bit of light is transmitted , The low transmittance most light is (high absorption) reading Blue absorbed indicates that chlorophyll light absorbs most blue light. © 2017 Pearson Education, Ltd  Examples of photosynthetic pigments Chlorophylls are excellent light absorbers because of their porphyrin ring system aromaticity. That is, they possess delocalized π electrons difference above and below the planar ring structure. The energy L difference between electronic states in these π-orbitals diff toi conjugated correspond to the energies of visible light photons. When system & ring It light energy is absorbed, an electron is promoted to a higher abs of light takes orbital, enhancing the potential for transfer of this electron to place in conjugated a suitable acceptor. Loss of such a photoexcited electron to systems an acceptor is an oxidation-reduction reaction. The absorption spectra of chlorophylls a and b differ somewhat. Plants that posses both chlorophylls can harvest a wider spectrum of incident energy. to anchor in membrane no significant abs & green/yellow chlorophylls & absorb lower & higher wavelengths Garett & Grisham: Biochemistry 4th edition  Absorption spectra of various photosynthetic pigments diff photosynthetic pigments all being able to absorb light, can make of entire use solar spectrum optimizat of absorbing , as much light photons , Voet, Voet: BIOCHEMISTRY 3rd edition  Examples of photosynthetic pigments Other pigments in photosynthetic organism, so- called accessory light harvesting pigments, increase the possibility for absorption of incident light of wavelengths not absorbed by the chloro- phylls. Carotenoids and lutein, like chlorophyll, possess many conjugated double bonds and thus absorb visible light. Carotenoids have two primary roles in photosynthesis-light harvesting and photo-protection through destruction of reactive oxygen species that arise as by- products of photo- excitation. © 2017 Pearson Education, Ltd Mathews, van Holde, Ahern: Biochemistry 3rd edition  Linear electron flow folding of memb. ↑ size & more p can be embedded evolutionnare - Cytochrome NADP+ reduce MADP to Photosystem II complex Photosystem I reductase O2 is generated MADPH 4 H+ Light Light NADP+ + H+ Fd Pq NADPH transport i ofmemb H2O e− e− Pc e-along ½ O2 pump It into THYLAKOID SPACE +2 H+ 4 H+ thylakoid space (high H+ concentration) from I cleavage ofHo give H + poton motive - To force Calvin Cycle Thylakoid [F-type) membrane ATP STROMA synthase + (low H concentration) ADP + ATP Pi H+ © 2017 Pearson Education, Ltd Garett & Grisham: Biochemistry 4th edition  A photosystem is composed of a reaction center complex surrounded by several light harvesting complexes absorb light Photon - Photosystem ② STROMA ① Light-harvesting Reaction- Primary complexes center electron complex acceptor Thylakoid membrane to ② Chlorophyll (green) STROMA Thylakoid membrane e− released O Transfer Special pair of Pigment of energy chlorophyll a molecules Protein provd by photons molecules subunits from one harvesiq THYLAKOID SPACE THYLAKOID (INTERIOR OF THYLAKOID) (purple) complex to another SPACE (a) How a photosystem harvests light (b) Structure of a photosystem © 2017 Pearson Education, Ltd  Excitation of isolated chlorophyll by light Excited e− state release energy Energy of electron in terms of Heat or Photon (fluorescence) Photon Ground Chlorophyll state molecule (a) Excitation of isolated chlorophyll molecule (b) Fluorescence © 2017 Pearson Education, Ltd  Light absorption and energy transfer Resonance transfer from I ground State Molecule I is excited to a higher energy state1 by absorbing a energyt neighbouring molecule photon. The excited molecule can dissipate its energy in the molecule becomes excited following ways: If there is a suitable (or identical) molecule close to it, the excitation energy can be transferred. When that happens, 1st molecule back molecule I comes back to its ground state, and molecule II goes goes to ground to an excited state. This process occurs among the light- State harvesting (or accessory) pigments. Mathews, van Holde, Ahern: Biochemistry 3rd edition Campbell: Biology in Focus 2nd edition  Light absorption and energy transfer Electron transfer ⚫ If molecule II is a suitable electron 2nd molecule acceptor, the excited electron from is molecule I can be transferred to molecule molecule II. This is photochemistry. In this case, molecule I becomes positively charged, and molecule II is in an excited state with a negative charge. The molecule that does photochemistry is called the reaction centre molecule. Both energy transfer and photochemistry are bimolecular reactions. movin g simultaneously within ps system Mathews, van Holde, Ahern: Biochemistry 3rd edition  Resonance and electron transfer in a light harvesting (LH) complex photochemistry taking place , tre - ve Lexcited) Schematic diagram of a photosynthetic unit. A photosynthetic unit can be envisioned as an antenna of several hundred light harvesting chlorophyll molecules plus a special pair of photochemically reactive chlorophyll a molecules called the reaction center. The purpose of the vast majority of chlorophyll in a photosynthetic unit is to harvest light incident within the unit and funnel it, via a resonance energy transfer, to the reaction center chlorophyll dimers that are photochemically acitve. Oxidation of chlorophyll leaves a cationic free radical, Chl +, whose properties as an electron acceptor have important consequences for photosynthesis. Mathews, van Holde, Ahern: Biochemistry 3rd edition D. L. Nelson, M. & M. Cox, Lehninger Principles of Biochemistry, 4th edition Campbell: Biology in Focus 2nd edition  The light reactions and chemiosmosis Cytochrome NADP+ Photosystem II complex Photosystem I reductase 4 H+ Light Light NADP+ + H+ Fd Pq NADPH e− Pc e− H2O THYLAKOID SPACE ½ O2 +2 H+ 4 H+ (high H+ concentration) To Calvin Cycle Thylakoid membrane ATP STROMA synthase + (low H concentration) ADP + ATP Pi H+ Cyanobacteria, green algae, and higher plants are oxygenice phototrophs, because they can generate O2 from water. They have two distinct photosystems: photosystem I (PSI) and photosystem II (PSII). Type I photosystems use ferredoxin as terminal electron acceptors; type II photosystems use quinones as terminal e- acceptor. PSI is defined by reaction center chlorophylls with max. red light absorption at 700 nm; PSII uses reaction centers that exhibit max. red light absorption at 680 nm. The reaction center Chl of PSI is referred to as P700 because it absorbs light of 700 nm wavelength; the reaction center Chl of PSII is called P680 for analogous reasons. Both P700 and P680 are chlorophyll a dimers situated within protein complexes. PSI provides the reducing power in the form of NADPH. PSII splits water, producing O2, and feeds the e- released into an e- transport chain that couples PSII and PSI. e- transfer between PSII and PSI pumps protons for chemiosmotic ATP synthesis. © 2017 Pearson Education, Ltd  The pathway of photosynthetic transfer The individual redox components of PSI and PSII are arranged as an e- transport chain according to there standard reduction potential, the zigzag result resembles the letter Z laid sideways. This “Z scheme” shows the pathway of electron transfer from H2O (lower left) to NADP (far right) in noncyclic photosynthesis. The position on the vertical scale of each electron carrier reflects its cascade of standard reduction potential. To raise the energy of electrons derived from H2O to the energy level e trsf required to reduce NADP to NADPH, each electron must be “lifted” twice (heavy arrows) by photons absorbed in PSII and PSI. One photon is required per electron in each photosystem. After excitation, the high-energy electrons flow “downhill” through the carrier chains shown. Protons move across the thylakoid membrane during the water-splitting reaction and during electron transfer through the cytochrome b6f complex, producing the proton gradient that is central to ATP formation. The dashed arrow is the path of cyclic electron transfer, which involves only PSI; electrons return via the cyclic pathway to PSI, instead of reducing NADP to NADPH. D. L. Nelson, M. & M. Cox, Lehninger Principles of Biochemistry, 4th edition  The mechanical analogy for linear electron flow during the light reaction D. L. Nelson, M. & M. Cox, Lehninger Principles of Biochemistry, 4th edition Campbell: Biology in Focus 2nd edition  Structure and function of plastoquinone in PSII ito ~ eacceptor [H] The structure o f plasto quinone A and its red uced form, Electrons flow from pheophytin via plastoquinone to a pool plastohydroquinone (or plastoquinol). Plastoquinone A has nine of plastoquinone with in the membrane. Because of its lipid isoprene units and is the most abundant Lembedded nature, plastoquinone is mobile within the membrane and plastoquinone in plants and algae. hence serves to shuttle e- from the PSII to the cytochrome b6f in I memb complex. Alternative oxidation-reduction of plastoquione to its hydroquinone form involves the uptake of protons. Note that plastoquinone is an analog of coenzyme Q, the mitochondrial electron carrier. Garett & Grisham: Biochemistry 4th edition D. L. Nelson, M. & M. Cox, Lehninger Principles of Biochemistry, 4th edition  The cytochrome b6f complex in PSII cy + bo Cytochrome b6f complex. The heme groups of cytochromes b6N, b6P, and f are shown in red; the iron-sulfur clusters are blue. Cytochrome b6f complex or plastoquinol:plastocyanin oxidoreductase possesses 26 transmembrane α-helices. The protein is structurally and functionally homolougs to the cytochrome bc1 complex (Complex III) of mitochondria. It includes the two heme-containing e- transfer proteins for which it is named, as well as iron-sulfur clusters, which also participate in e- transport. The purpose of this complex is to mediate the transfer of e- from PSII to PSI and to pump H+ across the thylakoid membrane via the Q-cycle. Cytochrome f is a c-type cytochrome. Cytochrome b6 in two forms (low and high potential) participates in the oxidation of plastoquinol and the Q cycle of the b6f complex. Garett & Grisham: Biochemistry 4th edition  Plastocyanin transfers electrons from cytochrome b6f to PSI A copper protein plastocyanin Plastocyanin (PC) is a 10.4 kDa protein with a copper atom bound. PC functions as a single e- carrier as its copper atom undergoes alternate oxidation-reduction between Cu+ and Cu2+ states. PSI is a light-driven plastocyanin:ferredoxin oxidoreductase. When P700 is excited by light and oxidized by transferring its e- to an adjacent Chl a molecule that serves as its immediate e- acceptor and P700+ is formed. P700+ readily gains an electron from plastocyanin. Voet, Voet: BIOCHEMISTRY 3rd edition Garett & Grisham: Biochemistry 4th edition  Linear electron flow from PS II to I and light absorption in PS I Electron Electron transport Primary e- transport Primary chain acceptor chain acceptor Pq e− Fd NADP+ 2 H+ H2 O e− e− e− + H+ + Cytochrome NADP+ complex reductase 1/2 O2 NADPH e− Pc P700 enter e e− P680 calvin cce Light Light ATP enter Calvin cycle Pigment molecules Photosystem I Photosystem II (PS I) (PS II) © 2017 Pearson Education, Ltd  Energetics of two light reactions ⚫ All these constitute an electron transfer chain from water to NADP+. Electron transfer is coupled with H+ transport. 2Fd (red) + H + + NADP+ Reductase 2Fd (ox) + NADPH The X-ray structure of the pea ferredoxin–NADP+ reductase (FNR) in complex with FAD and NADP+. Mathews, van Holde, Ahern: Biochemistry 3rd edition Voet, Voet: BIOCHEMISTRY 3rd edition Coffee break  Photophosphorylation: ATP synthase (CF1FO) uses ∆pH to make ATP Cytochrome NADP+ Photosystem II complex Photosystem I reductase 4 H+ Light Light NADP+ + H+ Fd Pq NADPH e− Pc e− H2O THYLAKOID SPACE ½ O2 +2 H+ 4 H+ (high H+ concentration) To Calvin Cycle Thylakoid membrane ATP STROMA synthase + (low H concentration) ADP + ATP Pi H+ © 2017 Pearson Education, Ltd  The mechanism of photophosphorylation in chemiosmotic Experimental proof that the mechanism of photophosphorylation is chemiosmotic was provided in an elegant experiment by Andre Jagendorf and Ernest Uribe in 1966. Jagendorf and Uribe reasoned that if photophosphorylation were indeed driven by an electrochemical gradient established by photosynthetic electron transfer reactions, they might artificially generate such a gradient by first incubating chloroplasts in an acid bath in the dark and then quickly raising the pH of the external medium. The resulting inequality in hydrogen ion electrochemical activity across the membrane should mimic the conditions normally found upon illumination of chloroplasts and should provide the energized condition necessary to drive ATP formation. To test this interpretation, they bathed isolated chloroplasts in a weakly acidic (pH 4) medium for 60 seconds, allowing the pH inside the chloroplasts to equilibrate with the external medium. The pH of the solution was then quickly raised to slightly alkaline pH (pH 8), artificially creating a pH gradient across the thylakoid membranes. When ADP and Pi were added, ATP synthesis was observed as the pH gradient collapsed. Photophosphorylation then can be summarized by noting that thylakoid vesicles accumulate H+ upon illumination and that the electrochemical gradient thus created represents an energized state that can be tapped to drive ATP synthesis. Collapse of the gradient—that is, equilibration of the ion concentration difference across the membrane—is the energy-transducing mechanism: the chemical potential of a concentration difference is transduced into synthesis of ATP. Garett & Grisham: Biochemistry 4th edition  Cyclic photophosphorylation generates ATP but not NADPH or O2 produced e- trsf e back to PSI pumps In cyclic photophosphoylation, the “e- hole” in P700+ created by e- loss from P700 is filled not by an e- derived from H2O via PSII but by a cyclic pathway in which the photoexited e- returns ultimately to P700+. This pathway diverts the activated e- lost from PSI back through the PQ pool, the cytochrome b6f complex, and plastocyanin to re-reduce P700+. H+ trans- location accompany these e- transfer events so that ATP synthesis can be achieved. In cyclic photophosphorylation, ATP is the sole product of energy conversion. No NADPH is generated, and because PSII is not involved, no oxygen is evolved. & NADP reductase not involved Garett & Grisham: Biochemistry 4th edition  Light reactions of photosynthesis ⚫ The phase of light reactions consists of several distinct events: (a) Light absorption and energy transfer (b) Photochemistry (c) Water-splitting (d) Electron transfer and formation of proton gradient (e) ATP synthesis (photophosphorylation) ⚫ Light is absorbed by molecules called pigments. The most common class of natural pigments are chlorophylls.  An overview of photosynthesis Light H2O CO2 NADP+ ADP + LIGHT Pi CALVIN REACTIONS CYCLE ATP Thylakoid Stroma NADPH Chloroplast O2 [CH2O] (sugar) © 2017 Pearson Education, Ltd  Schematic view of the Calvin cycle + IG GC cleared to give (x2) (5C) used CHY Carbon dioxide fixation is accomplished by adding one CO2 at a time to an acceptor molecule Ribulose-1,5-bisphosphate (RuBP) and passing the molecule through a cyclic series of reaction, called Calvin cycle. The cycle results in the formation of hexoses and in the regeneration of the acceptor molecule. The Calvin cycle can be divided into two stages. Stage I, the carbon dioxide is trapped as a carboxylate and reduced to the aldehyde-ketone level found in sugars, resulting in net carbohydrate synthesis. Stage II is dedicated to regenerating the acceptor molecule. Mathews, van Holde, Ahern: Biochemistry 3rd edition  The process of CO2 fixation in the Calvin cycle hydrated cleavage ~ real molecule that is fixing it is The true substrate for the carbon dioxide fixation is the enediol intermediate, and the product is hydrated and then cleaved to yield 2 molecules 3-phosphoglycerate. The reaction is essentially irreversible. The key reaction of CO2 fixation is catalyzed by ribulose bisphosphate carboxylase/oxygenase (rubisco). The name reflects that rubisco catalyzes the reaction of CO2 or, alternatively, O2 with RuBP. It is probably the world’s most abundant protein. As shown in the structure of rubisco (left) the enzyme consists of 8 equivalents each of two subunits. Clusters of small subunits (orange and red) are located at each end of the octamer. The active sites are revealed in the ribbon diagram by bound ribulose-1,5-bisphosphate (yellow). 8 active sites Mathews, van Holde, Ahern: Biochemistry 3rd edition Garett & Grisham: Biochemistry 4th edition  Stage I of the Calvin cycle release of phosphate [o) & [H) At this stage of the cycle a molecule of CO2 has already been fixed into a three carbon monosaccharide. It is useful to note the requirements in ATP and NADPH up to this point. For each CO2 molecule that has passed through these steps, two molecules of ATP have been hydrolyzed and two molecules of NADPH have been oxidized. Mathews, van Holde, Ahern: Biochemistry 3rd edition  Stoichiometry of the Calvin cycle In six turns of the Calvin cycle, 6 CO2 molecules will have entered and bound to 6 molecules of ribulose-1,5- ~ bisphosphate (RuBp) to yield 12 to get a 60 molecules of glyceraldehyde -3- molecule ribuloce-1 , 5-bisphosphate phosphate (G3P). Since G3P is in isomeric equilibrium with learned dihydroxyacetone phosphate (DHAP), - in the 12 G3P may be considered an glycolysis interconvertible stock of 12 molecules of (G3P + DHAP). Of these, 6 are used to make 3 molecules of fructose-1,6- bisphosphate (FBP), of which one constitutes the next hexose product of the 6 turns. The other 2 FBPs are used, together with the 6 remaining molecules of ribulose-5-phosphate (Ru5P), which are then phosphorylated to regenerate the required 6 molecules of RuBP. ~ glucose-6-phosphate Mathews, van Holde, Ahern: Biochemistry 3rd edition  Schematic view of the Calvin cycle Mathews, van Holde, Ahern: Biochemistry 3rd edition  The Calvin cycle regenerat of RuBP come from diff can sources CO2 fixat" precurser for & other carbohydrates (to generate C6 , C7, 25, etc molecules all don'treed to know e details Voet, Voet: BIOCHEMISTRY 3rd edition  The role of photosynthesis in metabolism 3[ by-pot ↑ provide sufficient energy Mathews, van Holde, Ahern: Biochemistry 3rd edition  Animation Photosynthesis © 2017 Pearson Education, Ltd  SINGAPORE: Think of mangroves as a bank account, but instead of storing money, this account stores carbon and actively takes in carbon dioxide from the atmosphere. And while Singapore’s mangroves make up a small part of its total land area - about one per cent - they have a role to play when it comes to carbon storage. “What’s great about mangroves compared to other types of forests is that they store a lot more carbon (in the same amount of area),” Associate Professor Daniel Friess (NUS) told CNA. “Mangroves are great because they can store three to five times more carbon per hectare than other forest types (typically) do,” he explained. https://www.channelnewsasia.com/news/singapore  Quiz 1. What is the function of an uncoupler? Uncouplers act by dissipating the proton gradient across the inner mitochondrial membrane created by the electron-transport system. 2. What does Z-scheme mean? The individual redox components of PSI and PSII are arranged as an e- transport chain according to there standard reduction potential, the zigzag result resembles the letter Z laid sideways 3. Call the five distinct events in the phase of light reactions. (a) Light absorption and energy transfer (b) Photochemistry (c) Water-splitting PSI (d) Electron transfer and formation of proton gradient (e) ATP synthesis (photophosphorylation) Thank you!