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UI BIOL 1411 - Photosynhesis
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Biol 1411 1st Edition Lecture 13 Outline of Last Lecture I. Bioenergeticsa. Pyruvate Oxidationb. Citric Acid Cyclec. Oxidative Phosphorylationd. ChemiosmosisII. Fermentationa. Lactic Acidb. Alcohol fermentation anaerobic Outline of Current Lecture III. Photosynthesisa. Light Reactionsb. Light-dependent ReactionsCurrent 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- Photosynthesiso 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2Oo An endergonic, anabolic processo Sunlight provides the energyo This is a transformation of radiant energy to chemical energyo Involves Redox Reactions  CO2 is reduced to form carbohydrate H2O is oxidized to form oxygen - Chloroplastso Inner membraneo Outer membraneo Thylakoido Stroma- liquido Granum- stack of thylakoids- 2 pathways of photosynthesisThese 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 Spectrumo Light is a form of electromagnetic radiationo Light is propagated as waves- the energy of light is inversely proportional to its wavelengtho Light also behaves as particles, called photons - Exciting a Molecule: 3 things can happen when photon meets a moleculeo Scattered: photon bounces off the moleculeo Transmitted: photon is passed through the moleculeo 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 Chlorophyllo 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 transporto 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 centero Pigments are packed together on thylakoid membrane proteinso 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 Reactionso The PS reaction center Chl absorbs a photon and becomes excited =Chl*o Chl* donates an e- to an acceptor molecule, Ao A is the first in a chain of electron carriers in the thylakoid membraneo 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 ofthe water moleculeo 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 Photosystemso Photosystem I (second) Light energy reduces NADP+ to NADPH Reaction center has P700 chlorophyll a molecules: absorb in the 700 nm rangeo 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 photophosphorylationo Light-driven production of ATP by a chemiosmosis mechanismo 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


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UI BIOL 1411 - Photosynhesis

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