BIOL 1441 1st Edition Lecture 18 Outline of Last Lecture I Hydrogen gradient II ATP production III Fermentation IV Fermentation vs cellular respiration V Facultative anaerobes VI Versatility of catabolism VII Photosynthesis VIII Plant anatomy IX Redox reaction X Respiration vs photosynthesis XI Sunlight Outline of Current Lecture I Light properties II Photosynthetic pigments III Spectrophotometer IV Accessory pigments V Excitation of chlorophyll VI Photosystems These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute VII Light reaction VIII Linear electron flow IX Calvin cycle dark rxn Current Lecture I II III IV V Light Properties a Reflection bounces back i This is the color you see b Transmission passes through microscope c Absorption used as energy i Black objects reflect 0 light gain heat faster than white objects reflects all light ii Comes out of molecule at a lower energy level iii Fluorescence when light comes out as a lower wavelength and it releases a photon 1 seeing visible light UV light together d Refraction bending light Photosynthetic Pigments a Pigments absorb visible light b Different pigments absorb different wavelengths c Wavelengths not absorbed are reflected or transmitted d Leaves appear green chlorophyll reflects transmits green light i Means it doesn t use green wavelength Spectrophotometer a Measures pigment s ability to absorb various wavelengths b Sends light through pigments measures the fraction of light transmitted at each wavelength Accessory Pigments a Chlorophyll a main photosynthetic pigment b Chlorophyll b olive green c Carotenoids yellow orange absorb violet blue green light i In the fall when there is not as much sunlight there is not as much photosynthesis happening Carotenoids start breaking down pigments and that is why you see yellow orange colored leaves Excitation of Chlorophyll a Pigment absorbs light ground state to excited state unstable i Cant stay in excited state for very long b Molecule s electron elevated to an orbital with more potential energy further from nucleus c Photons absorbed are those whose energy is exactly equal to the energy difference between the ground state and the excited state VI VII i exact change has to be the exact wavelength d Varies from one molecule to another e Particular compound only absorbs photons corresponding to specific wavelengths unique absorption spectrum Photosystems where chlorophyll absorbs photons a Thylakoid membrane chlorophyll molecules organized along with other organic molecules proteins b Reaction center surrounded by light harvesting complexes c PASSES A PHOTON OF LIGHT d Rxn center 2 chlorophyll a molecules i Chlorophyll a special molecular environment enabling them to use energy from light to boost electrons to a higher energy level to transfer it ii Primary electron acceptor accepts excited electron from chlorophyll a 1 Oxidized chlorophyll a e Light harvesting complexes pigment molecules bound to proteins i Various pigments allows photosystem to absorb wider range of wavelengths ii Pigment absorb photon transfer the energy photon from pigment molecule to pigment molecule then to chlorophyll a molecules in rxn center f Two types of photosystems in thylakoid membrane i Photosystem I II PS I PS II ii Both contain a pair of chlorophyll a molecules g Photosystem II functions 1st in the light reaction P680 i Numbers reflect order of discovery ii Absorbs wavelength of 680 nm h Photosystem I absorbs wavelength of 700 nm P700 i Work together use light energy to generate ATP NADPH i 2 electron transport chains in between Photosystem I and II 1 First ETC makes ATP 2 Second ETC makes NADPH Light Reaction Redox a 1st step of light rxn s solar powered transfer of an electron from chlorophyll a to primary electron acceptor b As soon as chlorophyll electron excites to a higher energy level primary electron acceptor captures it redox rxn c Chemiosmosis Chloroplasts Mitochondria i Both generate ATP by chemiosmosis different energy sources 1 Mitochondria transfer chemical energy from food to ATP 2 Chloroplasts transform light energy into the chemical energy ATP VIII ii ETC transform redox energy to a proton motive force drop in free energy from e transfer and proton gradient iii ATP synthase in membrane phosphorylates ADP iv Oxidative phosphorylation high energy electrons dropped down ETC extracted from organic molecules food v Photophosphorylation water is the source of electrons light energy drives electrons from water to top ETC vi Spatial organization of chemiosmosis differs in chloroplasts and mitochondria Linear Electron Flow a Step 1 photosystem II i Photon of light strikes pigment boosts electro to higher energy level excited redox reaction b Step 2 photosystem II i Photoexcited electron is transferred from excited P680 to primary electron acceptor 1 P680 P680 oxidized 2 P680 reduced state 3 P680 oxidized state c Step 3 photosystem II i Enzyme catalyzes splitting of H2O into two electrons 2 H O 1 Oxygen becomes the air we breath 2 H2O REDUCES P680 to P680 3 Oxidizing agent P680 d Step 4 photosystem II i Photoexcited electron passes fro primary electron acceptor of PS II to PS I through the ETC e Step 5 Photosystem II i Exergonic fall of electrons to lower energy level provides energy for ATP sytnthesis 1 Just like in respiration move electrons down to a more electronegative molecule drop in free energy ii PUMPS H INTO THYLAKOID SPACE DIFFUSES INTO STROMA f Step 6 photosystem I i P700 P700 1 Accepts electrons from bottom of ETC from PS II 2 FINAL ELECTRON ACCEPTOR IN 1ST ETC IS P700 3 P700 IS REDUCED BY FIRST ETC g Step 7 photosystem I i NO proton gradient ii NO ATP produced h Step 8 photosystem I IX i NADP reducase 1 Reduces NADP NADPH a Gives it electrons ii FINAL ELECTRON ACCEPTOR NADP Calvin Cycle dark rxn a Anabolic rxn building molecules requires energy i Builds sugar using ATP NADPH from light rxn b Carbon enters the cycle as CO2 i CO2 fees in one at a time c Leaves as glyceraldehyde 3 phosphate G3P d For net synthesis of one G3P cycle must take place three times fixing three molecules of CO2 i Fixing inorganic organic e Sugar produced is not glucose f Produces glyceraldehyde 3 phosphate G3P i 3 carbon sugar g Three phases i Carbon fixation 1 3CO2 enters cycle 2 Rubisco enzyme that puts CO2 and RuBP together forms 3phosphoglycerate 3 RuBP CO2 acceptor ii Reduction 1 MAKE SUGAR a ONLY 1