Photosynthesis

  1. Photosynthesis    Ecological importance    Photoautotrophs fix organic C (CO2); producers    Heterotrophs obtain C material from organic sources (other organisms); consumers    All energy from sun, flows through system    Redox; H2O oxidized to O2, CO2 reduced to C6H12O6    Endergonic -> E boost from light E; + delta G    Energy + 6CO2 + 6H2O -> C6H12O6 + 6O2    Nature of light    Light = form of electromagnetic E, radiation travels in waves    Photon: small particle of light E    E in photon: shorter wavelength = > energy/photon; longer wavelength = < energy/photon    Effects of photon on e-    Molecule absorbs photon light E -> e- energized -> shifts to higher e-    Can return to lower E orbital or leave atom -> captured by e- acceptor -> acceptor reduced    Plant organization    Absorbs visible light (red,blue); leaves are green bc chlorophyll reflects/transmits green light; chloroplasts are photosynthetic organelle    Structure of chloroplasts: 2 outer membranes, inner membrane = thylakoid, inner cytosol is stroma    Photosynthetic pigments    Chlorophyll is pigment, head absorbs visible light and has HC tails    Chlorophyll a is main one    Overview of photosynthesis    All E from sun, flows through system    Redox: H2O oxidized, CO2 reduced    Endergonic: E boost from light E; + delta G    Light dependent reactions    Light reactions in thylakoid (membrane), split H2O, release O2, reduce NADP+ -> NADPH, generates ATP from ADP    PS I/II trap sun energy, converted -> NADPH/ATP    Most reactions are linear e- flow (excite e-/use E/replace e-)    Light-dependent, PSII/PSI, ATP/NADPH/O2, more recent: cause of O2 revolution    Cyclic e- flow: only produces ATP, older so predates O2 revolution (@ PSI)    Photosystems    2 light-harvesting complexes: PS I (700) and PS II (680)    Capture light/produce ATP/NADH; each has pigment (680/700) capturing specific wavelength    2 ETCs    Protein chain pass e- from 2 protein to next (redox), each time some E from excited e- used/lost    PSII ETC uses e- -> pumps H+ -> fill thylakoid with H+    PSI ETC: catalyzes building NADPH    ATP synthase: protein (proton channel) and as H+ flow -> catalyzes ADP + Pi -> ATP    Light reaction builds 2 molecules: ATP is cellular E, NADPH is e- carrier    Boost PSII e-    Photon hits pigment, E passed to 680 (reaction center), 680 oxidized to P680+, excited e- transformed to 1^o e- acceptor (redox)    Use E in e- passed down ETC -> ATP    E- from 1^o e- acceptor -> ETC (Pq oxidized, Cyt reduced)    Passed from protein to protein, H+ pumped into thylakoid    Generates H+ gradient in thylakoid space (acidic in lumen)    H+ diffuses through ATP synthase (fac. diffusion) in ATP synthesis    Replace PSII e- from H2O    P680+ is oxidizing agent -> H2O oxidized (photolysis) to replace e-    e- -> P680+ -> P680+ reduced to P680; O2 is product; now e- has low E    Boost PSI e-    Light E excited e- in pigments -> excited P700 -> oxidized to P700+ -> e- acceptor reduced    Use E in e- (make NADPH)    e- moves through PSI ETc -> Ferredoxin (Fd)    e- transferred -> enzyme NADP+ reductase    NADP+ + e- + H+ -> NADPH    Replace PSI e- (with PSII e-)    PSII e- -> ETC -> uses E    Low E e- donated to PSI to replace lost e-

ETC Pigment Both purpose PSII Uses e- to pump H+ -> fill thylakoid with H+ P680 Light dependent Trap sun energy -convert -> NADPH/ATP PSI Catalyzes building NADPH P700 -cyclic e- flow

Carbon fixation reactions (stroma): Reduce CO2 -> C6H12O6 using NADPH/ATP 3C enter as CO2; CO2 + RuBP; catalyzed by Rubisco -> 6 PGAs (phosphoglycerides, 3 C each) Carbon reduction: 6 PGA use 6 ATP -> bi-phosphoglycerate -> reduced with 6 NADPH -> 6 G3P -> 1 G3P leaves to be sugar Regeneration: 5-3 carbon G3P; Converted -> 3 mol. 6 C RuBP with 3 ATP