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Photosynthesis Chapter 8 Copyright The McGrawHill Companies Inc Permission required for reproduction or display RoyaltyFreeICorbis Photosynthesis amp Respiration Sugars are made with solar energy via ATP in photosynthesis and cellular respiration converts the energy of sugars back to ATP as needed Overview of Photosynthesis Solar energy drives ATP amp NADPH drive production of energyrich conversion of 302 to ATP amp NADPH energyrich sugar solar energy Chloroplast Ls Leaf cross section Plant photosynthesis occurs in chloroplasts o 39 1 l 39 Y I I I s I u a p I a a O I 39 quot a 7 I 0 39 quot7 s a quotJ r p g I I I 39 c r a 39 r V I Stomata 002 02 Outer membrane Chlroplast Mesophyce Inner membrane 2 Stroma 39 Thylakoids Thylakoid membrane Innerer membrane folded into stacks of poker chips Thylakoid space Inside the poker chips Stro a Ganum Thylakoid In both mitochondria and chloroplasts Carbon conversion cycles in fluid space Electron transport chain amp ATP synthase on inner membranes Photosynthesis Respiration in reverse Photosynthesis Respiration End with ETC End by making water End by making ATP Load up electron carriers in cycle phase then use electrons in ETC Cycle phase breaks down molecules into CO2 02 in CO2 out Start with ETC Start by splitting water First make ATP Load up electron carriers in ETC then use electrons in cycle phase Cycle phase builds molecules from C02 C02 in 02 out Similar processes different anatomy Respiration ETC proteins High proton concentration in Intermembrane space Low proton concentration in Matrix NAD amp FADH Citric Acid Cycle in Matrix Photosynthesis Photosystem amp N High proton concentration in Thylakoid space Low proton concentration in Stroma NADP NADPH Calvin Cycle in Stroma Light energy 391 A 7quot l 243 7 v I fPhotosyrI thesis quot39 in chloroplasts i 2 I LOW 002 H20quot 353333 0 High energy Celluler respiration g 4 In niltochondrra J energy l v 7 I ATP powers most cellular work I 1 Heat energy Copyright 3 2038 Pearson Education inc publishing as Pearson Benjamin Cummings And there are many similarities Both have ETC to create a proton gradient Proton gradient is used to crank ATP Synthase A cycle phase dealing with carbon Photosynthesis Overview Energy for all life on Earth ultimately comes from photosynthesis esoo2 6H20 gt 06H1206 6o2 Oxygenio photosynthesis is carried out by Cyanobaoteria 7 groups of algae All land plants chloroplasts More Chloroplast Thylakoid membrane internal membrane Contains chlorophyll and other photosynthetic pigments Like Inner membrane of mitochondria Stroma Semifluid liquid surrounding thylakoid membranes Like matrix in mitochondria Thylakoid space inside the Thylakoid stacks grana Like the intermembrane space in mitochondria Chloroplast Outer membrane lntermembrane Stroma space Inner membrane 12 Granum Thylakoid membrane Thylako39d 395 quot l Stroma 13 Two Stages 1 Lightdependent reactions Require light Capture energy from sunlight Make ATP and reduce NADP to NADPH 2 Carbon fixation reactions or light independent reactions Does not require light Use ATP and NADPH to synthesize organic molecules from 302 Calvin Chloroplast Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings THE NITTYGRITTY Pigments Molecules that absorb light in the visible range Light is a form of energy Photon particle of light Acts as a discrete bundle of energy Energy content of a photon is inversely proportional to the wavelength of the light Photoelectric effect removal of an electron from a molecule due to light energy 18 Copyright The McGraerll Companies Inc Pennissron required for reproduction or display A Increasing energy i V i Increasing wavelength 0001 nm 1 nm 10 nm 1000 nm 001 cm 1 cm 1 m 100 m I l UV Gamma rays Xrays light Infrared Radio waves Visible light I 400 nm 430 nm 500 nm 560 nm 600 nm 650 nm 740 nm 19 Pigments Organisms have evolved a variety of different pigments Rhodopsin Melanin others Only two general types are used in green plant photosynthesis Chlorophylls Carotenoids Chlorophylls Chlorophyll a Main pigment in plants and cyanobacteria Only pigment that can act directly to convert light energy to chemical energy Absorbs violetblue and red light Chlorophyll b Accessory pigment or secondary pigment absorbing light wavelengths that chlorophyll a does not absorb Carotenoids Can absorb photons with a wide range of energies but usually only in the blue range Also scavenge free radicals antioxidants Protective role 22 Absorption spectrum When a photon strikes a molecule its energy is either Lost as heat Absorbed by the electrons of the molecule Boosts electrons into higher energy level Absorption spectrum range and efficiency of photons that a molecule is capable of absorbing Copyright The McGraw Hill Companies Inc Permission required for reproduction or display high 39 carotenoids chlorophyll a Chlorophyll b A I C 9 12 g 3 8 0 lt1 low Wavelength nm Autumn u w Step 1 of Photosynthesis LightDependent Reactions LightDependent Reactions 1 Photon of light is captured by a pigment molecule 2 Pigment transfers this energy to an electron grabbed from water 3 High energy electrons move through proteins ETC to reduce NADP to NADPH and create a proton gradient 4 ATP Synthase produces ATP from ADP amp Pi Chloroplasts have two connected photosystems Photosystem l Functions like sulfur bacteria Photosystem ll Can generate an oxidation potential high enough to oxidize water Working together the two photosystems carry out a transfer of electrons that is used to generate both ATP and NADPH while creating a Proton Gradient In sequence Photosystem ll splits water to get electrons amp excite them with light energy Electrons transferred to Photosystem l Photosystem l transfers electrons ultimately to NADPt producing NADPH Proteins use energy of electrons to move H from Stroma to Thylakoid space proton gradient Oneway flow of electrons Water 9 P82 9 PS1 9 NADPH 29 Primary sleotro 0 acceptor I trans t 39 39 bn Cytochrome complex chain OLight gt Pigment molecules Photosystem 11 PS 11 Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Photosystem I P3 I 9quot 9 e NADP NADP H reductase NADPH Light 30 STROMA low H concentration Cytochrome Photosystem 1 complex Photosystem I 4H Light NADP v 7 39 39 reductase a Light NADP H imam mm 1miniiiquot 5 quot 39WWW uxixiiuiiiiiiiium Hlt39Q9 i lt77 7 4 H H 1 7 I I I Ul L r v t 4 439 AV V J V 7 gt 39 139 i 5 i v 39 73105 A 393 l 1 quot39 1 174 000001313013i yOCIDDDDDDDEMCIDUDCIDO o Hv V gt O i u n 4 b l I iisu mm WiztziliilQiii 39 To Calvin Cycle 39 A I 39 Iliam 39 t 39 v 39 39 gt 39 39 3 f 39 7 1 E m miimam I s Ii w g uwuu I g i mm 39 I I i 4 A l I I r t I 4 5 39 39WquotquotW i iiiiiii mum Thylakoid membrane ATP STROMA synthase low H concentration quot7 Hi l Copyright 2008 Pearson Education inc publishing as Pearson Benjamin Cummings 31 ATP Synthase action Proton gradient is used to synthesize ATP Chloroplast has ATP synthase enzymes in the thylakoid membrane Allows protons back into stroma Stroma also contains enzymes for the Calvin cycle reactions The LightDependent Reactions In Out Light ATP ADP NADPH R 02 NADP water The electron acceptor at the end of the electron transport chain in chloroplasts is AHg Bo2 oNAD DNADP ENADPH Step 2 of Photosynthesis Calvin Cycle Carbon Fixation Calvin Cycle To build carbohydrates cells use Energy ATP from lightdependent reactions Reduction potential NADPH from Photosystem co2 Calvin cycle Named after Melvin Calvin 1911 1997 Also called 33 photosynthesis Many steps but we will focus on only 3 Key step is attachment of 302 to RuBP to form PGA Uses the enzyme ribulose bisphosphate carboxylaseoxygenase or rubisco Rubisco 38 3 steps 1 Carbon fixation RuBP co2 gt PGA 2 Reduction PGA is reduced to G3P 3 Regeneration of RuBP PGA is used to regenerate RuBP 3 turns of Calvin Cycle incorporate enough carbon to produce a new extra G3P 6 turns incorporate enough carbon for 1 glucose Input 30Entering one CO2 at a time Phase 1 Carbon xation tie 3 Shortlived a intermediate 3 6 W Ribulose bisphosphate 3PhOSphogycerate FiuBP I C 6 i i 6ADP Calvi n I i C cle y GG C4349 13Bisphosphoglycerate 6 6 NADP 6Qi iL 6 W cheraIdehyde3phosphate if39ggg g 39 e 63quot i infis aji ism Glucose and other organic compounds 40 Output Copyright 2008 Pearson Education lnc publishing as Pearson Benjamin Cummings What is the role of ATP amp NADPH in Calvin Cycle NADPH electron carrier Provides electrons amp protons H ATP provides energy for reaction 302 H from NADPH HCOH 6 x HCOH glucose Output of Calvin cycle Glucose is not a direct product of the Calvin cycle GSP a 3 carbon sugar is the main product Used to form sucrose Major transport sugar in plants Disaccharide made of fructose and glucose Used to make starch Insoluble glucose polymer Stored for later use Used to make cellulose lignin Calvin Cycle In Out 002 ADP gti NADP GSP gtSucrose gtStarch gtEtc Photosynthesis Bioflix 45 Copyright The McGrawHill Companies Inc Permission required for reproduction or display Heat Electron Transport System Pyruvate VATP ADPPi j ATP ADPlPi 46 A little leaf anatomy Stoma not stroma leaf pores leaf s nose 302 in 02 out also H20 out Problems with Rubisco Under normal conditions Plenty of 002 O2 is leaving through leaf stoma noses Rubisoo adds RuBP to CO2 Uh oh Photorespiration Condition where too much 02 in a leaf and not enough CC2 because stoma are closed Rubisoo will then add RuBP to 02 Can t make sugar from oxygen Why close your nose When too hot lose too much water v Can t avoid losing water through stoma CO in 0 out Therefore To live in hot and dry environments two adaptations have arisen 1 C4 photosynthesis 2 CAM photosynthesis Types of photosynthesis 33 Plants that fix carbon using only C3 photosynthesis the Calvin cycle C4 and CAM Use PEP carboxylase not RuBP Greater affinity for 002 no oxidase activity Add 302 to PEP to form 4carbon molecule C4 spatial solution CAM temporal solution C4 plants Corn sugarcane sorghum and a number of other grasses Initially fix carbon using PEP carboxylase in outer mesophyll cells to form C4 C4 molecule is transported to inner bundle sheath cells Within the bundlesheath cells C4 is converted back into CC2 Carbon fixation then by rubisco and the Calvin cycle in the inner cells C4 leaf anatomy Mesophyll cell Photosynthetic cells of C4 lt Bundle plant leaf sheath C9quot Copyright 2008 Pearson Education lnc publishing as Pearson Benjamin Cummings 54 The C4 pathway 321 fesophyll oxaloacetate 4C PEP 3C A 39 Vascular ssue Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings 55 Why aren t all plants C4 C4 pathway although it overcomes the problems of photorespiration does have a cost To produce a single glucose requires 12 additional ATP compared to the Calvin cycle alone C4 photosynthesis is advantageous in hot dry climates where photorespiration would remove more than half of the carbon fixed by the usual C3 pathway alone CAM plants Many succulent waterstoring plants such as cacti pineapples and some members of about two dozen other plant groups Stoma open during the night and close during the day Reverse of what most plants do CAM plants Fix 302 using PEP carboxylase during the night and store as C4 in vacuole When stoma closed during the day return carbonstorage molecule to 302 High levels of 302 drive the Calvin cycle and minimize photorespiraticn Copyright The McGrawHill Companies Inc Permission required for reproduction or display Eric SederT om Stack 8 Associates 60 Compare C4 and CAM Both use both 33 and C4 pathways C4 The two pathways occur in different cells CAM C4 pathway at night and the C33 pathway during the day Sugarcane Pineapple C4 CAM C02 C02 MeSOPhYquot 0 CO2 incorporated Night cell Organic acid into fourcarbon Organic acid organic acids carbon fixation Bundle C02 CO2 Day sheath cequot 6 Organic acids release CO2 to Calvin cycle Sugar Sugar a Spatial separation of steps b Temporal separation of steps 62 Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings