AP Exam Review: Photosynthesis and Respiration AP Biology
AP Exam Review: Photosynthesis and Respiration AP Biology Photosynthesis: Life from Light and Air AP Biology 2007-2008 Chloroplasts leaves cross section absorb of leaf sunlight & CO2 CO2 chloroplasts in plant cell chloroplast AP Biology chloroplasts contain chlorophyll make energy & sugar chloroplast H+ Plant structure ATP + + H+ H H+ + H H + H+ H+ H+ + H H Chloroplasts double membrane stroma outer membrane thylakoid inner membrane fluid-filled interior thylakoid sacs grana stacks stroma Thylakoid membrane contains chlorophyll molecules electron transport chain ATP synthase H+ gradient built up within AP Biology thylakoid sac thylakoid granum Photosynthesis Light reactions light-dependent reactions energy conversion reactions convert solar energy to chemical energy ATP & NADPH Calvin cycle It’s not the Dark Reactions! light-independent reactions sugar building reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 AP Biology thylakoid chloroplast +H+ H+ H+ + + + H+ H+H +H+ H H H H Light reactions Electron Transport Chain like in cellular respiration proteins in organelle membrane electron acceptors NADPH proton (H+) gradient across inner membrane find the double membrane! ATP synthase enzyme AP Biology ATP +H+ H+ H+ H+ H+H + + + + H+H H H H ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP generates O2 AP Biology use electron carrier NADPH The ATP that “Jack” built photosynthesis respiration sunlight breakdown of C6H12O6 H+ H+ H+ moves the electrons H+ H+ H+ H+ H+ runs the pump pumps the protons builds the gradient drives the flow of protons through ATP synthase bonds Pi to ADP generates the ATP ADP + Pi … that evolution built ATP H+ AP Biology Pigments of photosynthesis How does this molecular structure fit its function? Chlorophylls & other pigments embedded in thylakoid membrane arranged in a “photosystem” collection of molecules AP Biology structure-function relationship A Look at Light The spectrum of color V AP Biology I B G Y O R Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll a absorbs best in red & blue wavelengths & least in green accessory pigments with different structures absorb light of different wavelengths chlorophyll b, carotenoids, xanthophylls Why are plants green? AP Biology Photosystems of photosynthesis 2 photosystems in thylakoid membrane collections of chlorophyll molecules act as light-gathering molecules Photosystem II reaction chlorophyll a center P680 = absorbs 680nm wavelength red light Photosystem I chlorophyll b P700 = absorbs 700nm wavelength red light AP Biology antenna pigments chlorophyll a ETC of Photosynthesis Photosystem II chlorophyll b Photosystem I AP Biology ETC of Photosynthesis sun 1 e e AP Biology Photosystem II P680 chlorophyll a Inhale, baby! ETC of Photosynthesis thylakoid chloroplast +H+ H+ H+ + + + H+ H+H +H+ H H H H ATP H+ +H+ H+ H+ + H H + + H+H+ H+ HH Plants SPLIT water! O H H 2 1 e e O O H H e e fill the e– vacancy AP Biology Photosystem II P680 chlorophyll a +H e- H+ e- ETC of Photosynthesis thylakoid chloroplast H+ +H+ H+ H+ + H H + + H+H+ H+ HH +H+ H+ H+ H+ H+H + + + + H+H H H H ATP 3 2 1 e e H+ 4 ATP H+ to Calvin Cycle H+ H+ H+ AP Biology Photosystem II P680 chlorophyll a H+ H+ + H+ H ADP + Pi ATP H+ H+ energy to build carbohydrates ETC of Photosynthesis e e sun 5 e AP Biology Photosystem II P680 chlorophyll a e Photosystem I P700 chlorophyll b ETC of Photosynthesis electron carrier 6 e e 5 sun AP Biology Photosystem II P680 chlorophyll a Photosystem I P700 chlorophyll b $$ in the bank… reducing power! ETC of Photosynthesis sun sun + + + H H + + H+ H + H H H+H+ H+ H + H to Calvin Cycle O split H2O ATP AP Biology ETC of Photosynthesis ETC uses light energy to produce ATP & NADPH go to Calvin cycle PS II absorbs light AP Biology excited electron passes from chlorophyll to “primary electron acceptor” need to replace electron in chlorophyll enzyme extracts electrons from H2O & supplies them to chlorophyll splits H2O O combines with another O to form O2 O2 released to atmosphere and we breathe easier! Photosynthesis: The Calvin Cycle Life from Air AP Biology 2007-2008 Light reactions Convert solar energy to chemical energy ATP ATP energy NADPH reducing power What can we do now? build stuff !! AP Biology photosynthesis How is that helpful? Want to make C6H12O6 synthesis How? From what? What raw materials are available? CO2 NADPH carbon fixation reduces CO2 NADP C6H12O6 AP Biology NADP From CO2 C6H12O6 CO2 has very little chemical energy fully oxidized C6H12O6 contains a lot of chemical energy highly reduced Synthesis = endergonic process put in a lot of energy Reduction of CO2 C6H12O6 proceeds in many small uphill steps each catalyzed by a specific enzyme using energy stored in ATP & NADPH AP Biology From Light reactions to Calvin cycle Calvin cycle chloroplast stroma Need products of light reactions to drive synthesis reactions stroma ATP NADPH ATP thylakoid AP Biology C C Calvin cycle C C C C C 3. Regeneration of RuBP C C C C C RuBP 3 ATP C= C= C H H H | | | C– C– C AP Biology C C C C C C C C C C C C C C C C C C 1. Carbon fixation 5C C C C C C C RuBisCo ribulose bisphosphate carboxylase 3 ADP used to make glucose CO2 C C C C C ribulose bisphosphate starch, sucrose, cellulose & more 1C C C C C C C C 6C C C C C C C 5C glyceraldehyde-3-P G3P C C C PGA phosphoglycerate 3C 6 NADP C C C C C C 6 ATP 2. Reduction 6 NADPH 3C C C C C C C 3C 6 ADP C C C C C C H | H | H | Light Reactions H2O + light energy H2O Energy Building Reactions NADPH ATP O2 + NADPH + O2 produces ATP produces NADPH releases O2 as a waste product sunlight AP Biology ATP Calvin Cycle CO2 + ATP + NADPH C6H12O6 CO2 ADP NADP Sugar Building Reactions NADPH ATP AP Biology sugars + ADP + NADP builds sugars uses ATP & NADPH recycles ADP & NADP back to make more ATP & NADPH Putting it all together light CO2 + H2O + energy C6H12O6 + O2 H2O CO2 sunlight ADP NADP Sugar Energy Building Building Reactions Reactions NADPH ATP AP Biology O2 sugars Plants make both: energy ATP & NADPH sugars Cellular Respiration Harvesting Chemical Energy ATP AP Biology 2006-2007 Harvesting stored energy Glucose is the model respiration catabolism of glucose to produce ATP glucose + oxygen energy + water + carbon dioxide C6H12O6 + 6O2 ATP + 6H2O + 6CO2 + heat COMBUSTION = making a lot of heat energy by burning fuels in one step uel AP Biology carbohydrates) RESPIRATION = making ATP (& some heat) by burning fuels in many small steps ATP enzymes O2 ATP O2 CO2 + H2O + ATP (+ heat) glucose CO2 + H2O + heat How do we harvest energy from fuels? Digest large molecules into smaller ones break bonds & move electrons from one molecule to another as electrons move they “carry energy” with them that energy is stored in another bond, released as heat or harvested to make ATP loses e- gains e- + oxidized reduced + + e- oxidation AP Biology – e- reduction e- redox How do we move electrons in biology? Moving electrons in living systems electrons cannot move alone in cells electrons move as part of H atom e p move H = move electrons loses e- gains e- oxidized + + oxidation reduced + – H reduction H oxidation C6H12O6 + AP Biology H e- 6O2 6CO2 + 6H2O + ATP reduction Coupling oxidation & reduction REDOX reactions in respiration release energy as breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms C6H12O6 CO2 = the fuel has been oxidized electrons attracted to more electronegative atoms in biology, the most electronegative atom? O2 H2O = oxygen has been reduced O couple REDOX reactions & 2 use the released energy to synthesize ATP oxidation C6H12O6 + AP Biology 6O2 6CO2 + 6H2O + ATP reduction Oxidation & reduction Oxidation Reduction adding O removing H loss of electrons releases energy exergonic removing O adding H gain of electrons stores energy endergonic oxidation C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction AP Biology like $$ in the bank Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around NAD+ NADH (reduced) FAD+2 FADH2 (reduced) NAD+ nicotinamide Vitamin B3 niacin O– O– P O –O NADH O H C H –O AP Biology reduction oxidation adenine ribose sugar O C phosphates O– O– P O H H NH2 N+ + reducing power! carries electrons as a reduced molecule N+ O– O– P O –O O– O– P O –O NH How efficient! Build once, use many ways Overview of cellular respiration 4 metabolic stages Anaerobic respiration 1. Glycolysis respiration without O2 in cytosol Aerobic respiration respiration using O2 in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C H O6 + AP Biology 6 12 6O2 ATP + 6H2O + 6CO2 (+ heat) H+ And how do we do that? H+ H+ H+ H+ H+ H+ H+ ATP synthase enzyme H+ flows through it conformational changes bond Pi to ADP to make ATP set up a H+ gradient allow the H+ to flow ADP down concentration gradient through ATP synthase ADP + Pi ATP But… How is the proton (H+) gradient formed? AP Biology + P ATP H+ Cellular Respiration Stage 1: Glycolysis AP Biology 2007-2008 Glycolysis Breaking down glucose “glyco – lysis” (splitting sugar) glucose pyruvate 2x 3C 6C ancient pathway which harvests energy where energy transfer first evolved transfer energy from organic molecules to ATP still is starting point for ALL cellular respiration but it’s inefficient generate only 2 ATP for every 1 glucose occurs in cytosol AP Biology That’s not enough ATP for me! In the cytosol? Why does that make evolutionary sense? Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle AP Biology 2006-2007 Glycolysis is only the start Glycolysis glucose pyruvate 6C 2x 3C Pyruvate has more energy to yield 3 more C to strip off (to oxidize) if O2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO2 pyruvate CO2 AP Biology 3C 1C Cellular respiration AP Biology Mitochondria — Structure Double membrane energy harvesting organelle smooth outer membrane highly folded inner membrane cristae intermembrane space fluid-filled space between membranes matrix inner fluid-filled space DNA, ribosomes enzymes free in matrix & What cells would have AP Biology a lot of mitochondria? outer intermembrane membrane inner space membrane-bound membrane cristae matrix mitochondrial DNA Mitochondria – Function Oooooh! Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes & permeases bacteria! What does this tell us about the evolution of eukaryotes? Endosymbiosis! AP Biology Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases Oxidation of pyruvate Pyruvate enters mitochondrial matrix [ 2x pyruvate acetyl CoA + CO2 3C 2C 1C NAD Where does the CO2 go? Exhale! 3 step oxidation process releases 2 CO2 (count the carbons!) reduces 2 NAD 2 NADH (moves e ) produces 2 acetyl CoA Acetyl CoA enters Krebs cycle AP Biology ] Pyruvate oxidized to Acetyl CoA NAD+ Pyruvate C-C-C [ reduction Coenzyme A CO2 Acetyl CoA C-C oxidation 2 x Yield = 2C sugar + NADH + CO2 AP Biology ] Krebs cycle 1937 | 1953 aka Citric Acid Cycle in mitochondrial matrix 8 step pathway each catalyzed by specific enzyme Hans Krebs 1900-1981 step-wise catabolism of 6C citrate molecule Evolved later than glycolysis does that make evolutionary sense? bacteria 3.5 billion years ago (glycolysis) free O2 2.7 billion years ago (photosynthesis) eukaryotes 1.5 billion years ago (aerobic AP Biology respiration = organelles mitochondria) Count the carbons! pyruvate 3C 2C 6C 4C This happens twice for each glucose molecule 4C citrate oxidation of sugars 4C 6C CO2 x2 4C AP Biology acetyl CoA 5C 4C CO2 Count the electron carriers! pyruvate 3C 6C 4C NADH This happens twice for each glucose molecule 2C 4C citrate reduction of electron carriers x2 4C FADH2 4C AP Biology acetyl CoA NADH 6C CO2 NADH 5C 4C ATP CO2 CO2 NADH Value of Krebs cycle? If the yield is only 2 ATP then how was the Krebs cycle an adaptation? value of NADH & FADH2 electron carriers & H carriers reduced molecules move electrons reduced molecules move H+ ions to be used in the Electron Transport Chain like $$ in the bank AP Biology ATP accounting so far… Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! There’s got to be a better way! I need a lot more ATP! AP Biology A working muscle recycles over 10 million ATPs per second There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient yields ~36 ATP from 1 glucose! only in presence of O2 (aerobic respiration) AP Biology That sounds more like it! O2 Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes AP Biology Oooooh! Form fits function! Electron Transport Chain Inner mitochondrial membrane Intermembrane space C Q NADH dehydrogenase cytochrome bc complex Mitochondrial matrix AP Biology cytochrome c oxidase complex Remember the Electron Carriers? Glycolysis glucose Krebs cycle G3P 2 NADH Time to break open the piggybank! AP Biology 8 NADH 2 FADH2 Electron Transport Chain Building proton gradient! NADH NAD+ + H e p intermembrane space H+ H+ H e- + H+ C e– NADH H FADH2 NAD+ NADH dehydrogenase inner mitochondrial membrane e– Q AP Biology H+ e– H FAD 2H+ + cytochrome bc complex 1 O2 H 2O 2 cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps?… Stripping H from Electron Carriers Electron carriers pass electrons & H+ to ETC H cleaved off NADH & FADH2 electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space H+ + H H+ TA-DA!! Moving electrons do the work! + H H+ H+ + H+ H+ H + H+ H H+ C e– NADH AP Biology + H H+ Q e– FADH2 FAD NAD+ NADH dehydrogenase e– 2H+ cytochrome bc complex + 1 H2O 2 O2 cytochrome c oxidase complex ADP + Pi ATP H+ But what “pulls” the electrons down the ETC? H2O O2 AP Biology electrons flow downhill to O2 oxidative phosphorylation Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy make ATP instead of fire! AP Biology “proton-motive” force We did it! Set up a H+ H+ H+ H+ gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + Pi ATP Are we there yet? AP Biology H+ H+ H+ H+ H+ ADP + Pi ATP H+ Chemiosmosis The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’s the point! AP Biology Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Electron transport C system Q NADH Acetyl-CoA 1. Electrons are harvested and carried to the transport system. NADH Krebs cycle e- e- FADH2 e- 2. Electrons provide energy to pump protons across the membrane. e- H2O 3. Oxygen joins with protons to form water. 1 O 2 +2 2H+ O2 H+ CO2 ATP Mitochondrial matrix AP Biology H+ ATP ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase even though this equation is a bit of a lie… it makes a better story Energy cycle sun Photosynthesis light CO2 + H2O + energy C6H12O6 + O2 plants CO2 glucose H2O animals, plants ATP C6H12O6 + O2 energy + CO2 + H2O Cellular Respiration AP Biology The Great Circle of Life,Mufasa! ATP O2
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