Biol 1411 1st Edition Lecture 13 Outline of Last Lecture I Bioenergetics a Pyruvate Oxidation b Citric Acid Cycle c Oxidative Phosphorylation d Chemiosmosis II Fermentation a Lactic Acid b Alcohol fermentation anaerobic Outline of Current Lecture III Photosynthesis a Light Reactions b Light dependent Reactions Current Lecture Autotrophs organism that is capable of living exclusively on inorganic materials water and some energy source such as sunlight Heterotrophs organisms that requires preformed organic molecules as food Photosynthesis o 6CO2 12H2O C6H12O6 6O2 6H2O o An endergonic anabolic process o Sunlight provides the energy o This is a transformation of radiant energy to chemical energy o Involves Redox Reactions CO2 is reduced to form carbohydrate H2O is oxidized to form oxygen Chloroplasts o Inner membrane o Outer membrane o Thylakoid o Stroma liquid o Granum stack of thylakoids 2 pathways of photosynthesis 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 o Light reactions convert light energy to chemical energy as ATP and NADPH in thylakoid o Light independent reactions use ATP and NADPH from light reactions plus CO2 to produce carbohydrates Calvin cycle carbon fixation Electromagnetic Spectrum o Light is a form of electromagnetic radiation o Light is propagated as waves the energy of light is inversely proportional to its wavelength o Light also behaves as particles called photons Exciting a Molecule 3 things can happen when photon meets a molecule o Scattered photon bounces off the molecule o Transmitted photon is passed through the molecule o Absorbed molecule acquires the energy of the photon The molecule goes from ground state to excited state Heat light fluorescence passed to a nearby molecule by resonance energy transfer Absorption Spectrum plot of wavelengths absorbed by a pigment Action spectrum plot of biological activity as a function of exposure to varied wavelengths of light Structure of Chlorophyll o Several types of thylakoid pigments absorb light energy used in photosynthesis Chlorophylls a and b Accessory pigments absorb in red and blue regions transfer the energy to chlorophylls carotenoids and phycobilins Energy transfer and electron transport o Pigments are arranged in antenna systems or light harvesting complexes o A photosystem consists of multiple antenna systems and their pigments and surrounds a reaction center o Pigments are packed together on thylakoid membrane proteins o Excitation energy passes from pigments that absorb short wavelengths to those that absorb longer wavelengths and ends up in the reaction center pigment Key Events of the Light Reactions o The PS reaction center Chl absorbs a photon and becomes excited Chl o Chl donates an e to an acceptor molecule A o A is the first in a chain of electron carriers in the thylakoid membrane o A final electron acceptor is NADP and become NADPH 2 Systems of electron transport o Noncyclic electron transport produces NADPH and ATP Light energy is used to oxidize water O2 and H and electrons After excitation by light Chl is an unstable molecule and seeks electrons Chl is a strong oxidizing agent and takes electrons from water splitting of the water molecule o Cyclic electron transport produces ATP only only happens in Photosystem I An alternative way of using light energy to make more ATP but no NADPH An e form an excited chlorophyll molecule cycles back to the same chlorophyll molecule Cyclic electron transport begins and ends in PS I Ultimate electron acceptor is back to chlorophyll molecule 2 Photosystems o Photosystem I second Light energy reduces NADP to NADPH Reaction center has P700 chlorophyll a molecules absorb in the 700 nm range o Photosystem II first Light energy oxidizes water O2 H and electron splitting water Reaction center has P680 chlorophyll a molecules absorb at 680nm Both non cyclic and cyclic electron transport drive photophosphorylation o Light driven production of ATP by a chemiosmosis mechanism o H is transported via electron carriers across the thylakoid membrane into the lumen creating an electrochemical gradient o Almost a parallel to proton gradient in mitochondria o Use the same ATP synthase to generate ATP