3Energy needs of life All life needs a constant input of energy Heterotrophs (Animals)get their energy from “eating others”eat food = other organisms = organic moleculesmake energy through respirationAutotrophs (Plants)get their energy from “self”get their energy from sunlightbuild organic molecules (food) from CO2make energy & synthesize sugars through photosynthesis
4Energy needs of life Heterotrophs Autotrophs consumers animals fungi most bacteriaAutotrophsproducersplantsphotosynthetic bacteria (blue-green algae)
5making energy & organic molecules from ingesting organic molecules How are they connected?Heterotrophsmaking energy & organic molecules from ingesting organic moleculesglucose + oxygen carbon + water + energydioxideC6H12O66O26CO26H2OATP+exergonicWhere’s the ATP?AutotrophsSo, 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 H2Oendergonicmaking energy & organic molecules from light energy+ water + energy glucose + oxygencarbondioxide6CO26H2OC6H12O66O2lightenergy+endergonic
6The Great Circle of Life,Mufasa! sunEnergy cyclePhotosynthesisplantsH2OCO2glucoseO2animals, plantsCellular RespirationATPThe Great Circle of Life,Mufasa!
7What does it mean to be a plant Need to…collect light energytransform it into chemical energystore light energyin a stable form to be moved around the plant & also saved for a rainy dayneed to get building block atoms from the environmentC,H,O,N,P,K,S,Mgproduce all organic molecules needed for growthcarbohydrates, proteins, lipids, nucleic acidsATPglucoseH2OCO2NPK…
8Plant structure Obtaining raw materials sunlight CO2 H2O nutrients leaves = solar collectorsCO2stomates = gas exchangeH2Ouptake from rootsnutrientsN, P, K, S, Mg, Fe…
11Chloroplasts absorb sunlight & CO2 Leaf Leaf Chloroplasts Chloroplasts containChlorophyllChloroplastmake energy & sugar
12Plant structure Chloroplasts Thylakoid membrane contains double membranestromafluid-filled interiorthylakoid sacsgrana stacksThylakoid membrane containschlorophyll moleculeselectron transport chainATP synthaseH+ gradient built up within thylakoid sacA 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.H+
14It’s the Dark Reactions! PhotosynthesisLight reactionslight-dependent reactionsenergy production reactionsconvert solar energy to chemical energyATP & NADPHCalvin cyclelight-independent reactionssugar production reactionsuses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6It’s the Dark Reactions!
15Light Reactions produces ATP produces NADPH H2OATPO2lightenergy+NADPHH2Osunlightproduces ATPproduces NADPHreleases O2 as a waste productEnergy BuildingReactionsNADPHATPO2
16Calvin Cycle builds sugars uses ATP & NADPH CO2C6H12O6+NADPATPNADPHADPCO2builds sugarsuses ATP & NADPHrecycles ADP & NADP back to make more ATP & NADPHADPNADPSugar BuildingReactionsNADPHATPsugarsC6H12O6
17Putting it all together CO2H2OC6H12O6O2lightenergy+H2OCO2Plants make both:energyATP & NADPHsugarssunlightADPNADPEnergy BuildingReactionsSugar BuildingReactionsNADPHATPsugarsC6H12O6O2
18Light reactions Electron Transport Chain electron acceptors membrane-bound proteins in organelleelectron acceptorsNADPHproton (H+) gradient across inner membraneATP synthase enzymeNot accidental that these 2 systems are similar, because both derived from the same primitive ancestor.
19The ATP that Jack built sunlight breakdown of C6H12O6 photosynthesisrespirationsunlightbreakdown of C6H12O6H+ADP + Pimoves the electronsruns the pumppumps the protonsforms the gradientdrives the flow of protons through ATP synthaseattaches Pi to ADPforms the ATP… that evolution builtATP
20ETC of RespirationMitochondria transfer chemical energy from food molecules into chemical energy of ATPuse electron carrier NADHNADH is an inputATP is an outputO2 combines with H+’s to form waterElectron is being handed off from one electron carrier to another -- proteins, cytochrome proteins & quinone lipidsSo what if it runs in reverse??generate H2O
21Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPHETC of PhotosynthesisTwo 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
22Pigments of photosynthesis Chlorophyll & other pigmentsembedded in thylakoid membranearranged in a “photosystem”structure-function relationship
24Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of lightchlorophyll aabsorbs best in red & blue wavelengths & least in greenother pigments with different structures absorb light of different wavelengthsWhy are plants green?
25Photosystems of photosynthesis 2 photosystems in thylakoid membranecollections of chlorophyll moleculesact as light-gathering “antenna complex”Photosystem IIchlorophyll aP680 = absorbs 680nm wavelength red lightPhotosystem IP700 = 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
26ETC of Photosynthesis Photosystem II Photosystem I 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 slide
27ETC of Photosynthesis to the Calvin Cycle 3 1 H+ 4 H+ PS 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.4H+ADP + PiATP
28ETC of Photosynthesis to the Calvin Cycle 3 1 2 H+ 4 H+ ATP ADP + Pi
29$$ in the bank… reducing power ETC of Photosynthesiselectron carrier6to the Calvin Cycle5Need a 2nd photon -- shot of light energy to excite electron back up to high energy state.2nd ETC drives reduction of NADP to NADPH.Light comes in at 2 points.Produce ATP & NADPH$$ in the bank… reducing power
30ETC of Photosynthesis split H2O 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 slidesplit H2O
31ETC of Photosynthesis ETC produces from light energy 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!
32Experimental evidence Where did the O2 come from?radioactive tracer = O186CO26H2OC6H12O66O2lightenergy+Experiment 16CO26H2OC6H12O66O2lightenergy+6CO26H2OC6H12O66O2lightenergy+Experiment 2Proved O2 came from H2O not CO2 = plants split H2O
35Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I)PS II generates energy as ATPPS I generates reducing power as NADPH1 photosystem is not enough.Have to lift electron in 2 stages to a higher energy level. Does work as it falls.First, produce ATP -- but producing ATP is not enough.Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!
36Cyclic photophosphorylation If PS I can’t pass electron to NADP… it cycles back to PS II & makes more ATP, but no NADPHcoordinates light reactions to Calvin cycleCalvin cycle uses more ATP than NADPHX
37Photosynthesis 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?…stay tuned for the Calvin cycle