3Energy needs of life All life needs a constant input of energy Heterotrophs (Animals)get their energy from “eating others”make energy through respirationAutotrophs (Plants)produce their own energy (from “self”)convert energy of sunlightbuild organic molecules (CHO) from CO2make energy & synthesize sugars through photosynthesisconsumersproducers
4making energy & organic molecules from ingesting organic molecules How are they connected?Heterotrophsmaking energy & organic molecules from ingesting organic moleculesglucose + oxygen carbon + water + energydioxideC6H12O66O26CO26H2OATP+oxidation = exergonicAutotrophsWhere’s the ATP?making energy & organic molecules from light energySo, in effect, photosynthesis is respiration run backwards powered by light.Cellular Respirationoxidize C6H12O6 CO2 & produce H2Ofall of electrons downhill to O2exergonicPhotosynthesisreduce CO2 C6H12O6 & produce O2boost electrons uphill by splitting H2Oendergonic+ water + energy glucose + oxygencarbondioxide6CO26H2OC6H12O66O2lightenergy+reduction = endergonic
5What does it mean to be a plant ATPNeed to…collect light energytransform it into chemical energyneed to get building block atoms from the environmentC,H,O,N,P,K,S,MgglucoseCO2H2ONPK…
6Plant structure Obtaining raw materials sunlight CO2 H2O nutrients leaves = solar collectorsCO2stomates = gas exchangeH2Ouptake from rootsnutrientsN, P, K, S, Mg, Fe…
8chloroplasts in plant cell chloroplasts contain chlorophyll absorb sunlight & CO2cross section of leafleavesCO2chloroplasts in plant cellchloroplasts contain chlorophyllchloroplastmake energy & sugar
9Plant structure Chloroplasts Thylakoid membrane contains ATPthylakoidChloroplastsdouble membranestromafluid-filled interiorthylakoid sacsgrana stacksThylakoid membrane containschlorophyll moleculeselectron transport chainATP synthaseouter membraneinner membranegranumstromathylakoidA typical mesophyll cell has chloroplasts, each about 2-4 microns by 4-7 microns long.Each chloroplast has two membranes around a central aqueous space, the stroma.In the stroma are membranous sacs, the thylakoids.These have an internal aqueous space, the thylakoid lumen or thylakoid space.Thylakoids may be stacked into columns called grana.
10It’s not the Dark Reactions! PhotosynthesisLight reactionslight-dependent reactionsenergy conversion reactionsconvert solar energy to chemical energyATP & NADPHCalvin cyclelight-independent reactionssugar building reactionsuses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6It’s not the Dark Reactions!
11Light reactions Electron Transport Chain thylakoidchloroplastH+Light reactionsH+ATPElectron Transport Chainproteins in organelle membraneelectron acceptorsNADPHproton (H+) gradient across inner membranefind the double membrane!ATP synthase enzymeNot accidental that these 2 systems are similar, because both derived from the same primitive ancestor.
12ETC of PhotosynthesisChloroplasts transform light energy into chemical energy of ATPuse electron carrier NADPHTwo places where light comes in.Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.Need to look at that in more detail on next slidegenerates O2
13Pigments of photosynthesis How does this molecular structure fit its function?Chlorophylls & other pigmentsembedded in thylakoid membranearranged in a “photosystem”collection of moleculesstructure-function relationship
15Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of lightchlorophyll aabsorbs best in red & blue wavelengths & least in greenaccessory pigments with different structures absorb light of different wavelengthschlorophyll b, carotenoids, xanthophyllsWhy are plants green?
16Photosystems of photosynthesis 2 photosystems in thylakoid membranecollections of chlorophyll moleculesact as light-gathering moleculesPhotosystem IIchlorophyll aP680 = absorbs 680nm wavelength red lightPhotosystem Ichlorophyll bP700 = absorbs 700nm wavelength red lightreaction centerPhotons are absorbed by clusters of pigment molecules (antenna molecules) in the thylakoid membrane.When any antenna molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule = the reaction center.At the reaction center is a primary electron acceptor which removes an excited electron from the reaction center chlorophyll a.This starts the light reactions.Don’t compete with each other, work synergistically using different wavelengths.antenna pigments
17ETC of Photosynthesis Photosystem II Photosystem I chlorophyll a chlorophyll bPhotosystem ITwo places where light comes in.Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.Need to look at that in more detail on next slide
18Photosystem II P680 chlorophyll a ETC of Photosynthesissun1ePS II absorbs lightExcited electron passes from chlorophyll to the primary electron acceptorNeed to replace electron in chlorophyllAn enzyme extracts electrons from H2O & supplies them to the chlorophyllThis reaction splits H2O into 2 H+ & O- which combines with another O- to form O2O2 released to atmosphereChlorophyll absorbs light energy (photon) and this moves an electron to a higher energy stateElectron is handed off down chain from electron acceptor to electron acceptorIn process has collected H+ ions from H2O & also pumped by Plastoquinone within thylakoid sac.Flow back through ATP synthase to generate ATP.Photosystem II P680 chlorophyll a
19Photosystem II P680 chlorophyll a Inhale, baby!ETC of PhotosynthesisthylakoidchloroplastH+H+ATPPlants SPLIT water!1OH2eOOHe-H++Heefill the e– vacancyPhotosystem II P680 chlorophyll a
20energy to build carbohydrates Photosystem II P680 chlorophyll a ETC of PhotosynthesisthylakoidchloroplastH+H+ATPeH+312eH+ATP4to Calvin CycleH+ADP + Pienergy to build carbohydratesPhotosystem II P680 chlorophyll aATP
21Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a ETC of Photosynthesiseesunfill the e– vacancye5Need a 2nd photon -- shot of light energy to excite electron back up to high energy state.2nd ETC drives reduction of NADP to NADPH.Light comes in at 2 points.Produce ATP & NADPHeePhotosystem I P700 chlorophyll bPhotosystem II P680 chlorophyll a
22ETC of Photosynthesis e e electron carrier 6 NADPH to Calvin Cycle 5 sunNADPH to Calvin CycleNeed a 2nd photon -- shot of light energy to excite electron back up to high energy state.2nd ETC drives reduction of NADP to NADPH.Light comes in at 2 points.Produce ATP & NADPHPhotosystem I P700 chlorophyll bPhotosystem II P680 chlorophyll a$$ in the bank… reducing power!
23ETC of Photosynthesis e e O split H2O H+ sun sun to Calvin Cycle ATP Two places where light comes in.Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.Need to look at that in more detail on next slideOto Calvin Cyclesplit H2OATP
24ETC of Photosynthesis ETC uses light energy to produce ATP & NADPHgo to Calvin cyclePS II absorbs lightexcited electron passes from chlorophyll to “primary electron acceptor”need to replace electron in chlorophyllenzyme extracts electrons from H2O & supplies them to chlorophyllsplits H2OO combines with another O to form O2O2 released to atmosphereand we breathe easier!
25Experimental evidence Where did the O2 come from?radioactive tracer = O186CO26H2OC6H12O66O2lightenergy+Experiment 16CO26H2OC6H12O66O2lightenergy+6CO26H2OC6H12O66O2lightenergy+Experiment 2Proved O2 came from H2O not CO2 = plants split H2O!
26Photosynthesis summary Where did the energy come from?Where did the electrons come from?Where did the H2O come from?Where did the O2 come from?Where did the O2 go?Where did the H+ come from?Where did the ATP come from?What will the ATP be used for?Where did the NADPH come from?What will the NADPH be used for?Where did the energy come from? The SunWhere did the electrons come from? ChlorophyllWhere did the H2O come from?The ground through the roots/xylemWhere did the O2 come from? The splitting of waterWhere did the O2 go? Out stomates to airWhere did the H+ come from? The slitting of waterWhere did the ATP come from?Photosystem 2: Chemiosmosis (H+ gradient)What will the ATP be used for?The work of plant life! Building sugarsWhere did the NADPH come from?Reduction of NADP (Photosystem 1)What will the NADPH be used for? Calvin cycle / Carbon fixation…stay tuned for the Calvin cycle