BIOL 3427 1st Edition Lecture 9Current LectureI. Two major processesa. Light reactions (Energy-transduction reactions)i. Light dependent reactionsii. Light energy used to form ATP and reduce electron carrier moleculesiii. (Coenzyme NADP+ NADPH)iv. Water split +Oxygen releasedb. Carbon fixation reactionsi. Dark reactions (light-independent)ii. Energy of ATP used to link CO2 inorganic form of Carbon to organic moleculeiii. Reducing power of NADPH used to reduce Carbon to simple sugarII. Photosystem components1. Antenna complexa. Pigment molecules gather light energy and funnel it to the reaction center (resonance energy transfer)2. Reaction centera. Special chlorophyll ab. Molecules convert light energy to chemical energyii. Photosystems 1. Photosystems Ia. P700 Chlorophyll a`s in reaction center absorb light optimally at 700 nMb. In stroma thylakoids2. Photosystem IIa. P680b. In grana thylakoidsc. Linked by ETCd. Work continuously and simultaneouslye. Light energy absorbed by P680f. Transfers energized electron to primary acceptor molecule photolysisi. 2H2O 4e +4H + O2ii. Contributes to protein concentration in thylakoid lumenThese 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.iii. Electrons replace those lost by P680 and energized by more light transfer on to primary acceptorIII. Electron Transport Chaina. Similar to respirationi. Protons pumped from stoma to thylakoid lumen as electrons passIV. Photophosphorylationi. Same chemi osmotic coupling mechanism used to produce ATPV. Photosystem Ia. Light energy absorbed by antenna molecules passed to P700b. Transfers energized electron to primary acceptor moleculec. P700 and lose electrons replaced by ETC between photosystemsd. Electrons pass through ETCVI. In summary, a. In light reactions, electrons flow from water through photosystems I and II to NADPb. Energy harvest (from 4 photons, 2 water molecules)i. 6 ATP and 6 NADPHc. Noncyclic photophosphorylationd. Cyclic photophosphorylationi. Photosystem I aloneii. Generates ATPiii. Does not release O2 or release NADPHVII. Carbon fixation reactionsa. ATP and NADPH generated by light reaction used to fix and reduce Carbon into simple sugarsb. How does CO2 get into plant cells?i. Through stomataVIII. C3 Pathwaya. Calvin Cycleb. Starts and ends with RuBP (5C sugar)c. 3 stagesi. CO2 “fixed” to RuBP, catalyzed by Rubiscoii. Phosphorylated by ATP, reduced by NADPH PGAL (3 C Sugar product, Glycerol, 3 Phosphate)iii. Regeneration of RuBPiv. Summary equation1. 3CO2 + 9 ATP + 6 NADPH +6H PGAL + 9ADP + 8Pi + 6 NADPH +3H2Ov. Immediate product1. PGALa. Transported from chloroplast to cytosoli. Can then be converted to sucroseb. Remains in chloroplasti. Can be converted to starch, stored at night, sucrose produced from starch, exportedIX. Photorespirationa. Rubisco has affinity for CO2 and O2b. If O2 is used, carbons in resulting molecule must be salvagedc. Involves:i. Chloroplastii. Peroxisomeiii. Mitochondriad. Yields no ATP or NADHe. Occurs with CO2 fixationf. Photorespirei. Dry, hot conditions (Stomata closed)X. C4 Pathwaya. In Mesophyll Cellsi. Hydrated form of CO2 joins with PEP via PEP carboxylase enzyme oxaloacetate (4 C sugar)b. In Bundle sheath cellsi. Malate is decarboxylated yielding CO2 (Calvin Cycle) and pyruvated (mesophyll to regenerate ATP)c. Spatial separation between C4 pathway and Calvin CycleXI. Kranz Anatomya. Vascular bundle surrounded by bundle-sheath cellsb. Surrounded by mesophyll cellsi. Wreath-like, concentric layersXII. C4 Pathwaya. More efficient than C3 Pathway aloneb. C4 “costs” more: 5 ATP instead of 3 to fix one but high CO2 and low O2 limits photorespirationc. C4 plants well adapted for increased light, increased temperature, and decreased soil moistured. Evolved independently, multiple timese. Angiospermsf. 19 familiesi. 3 monocotsii. 16 eudicotsXIII. CAM Plantsa. Crassulacean acid metabolismb. Evolved independently in many succulentsc. Use both C4 and C3 Pathwaysd. Temporal separation of pathwayse. Night: Open stomata and fix CO2 with C4 Pathwayf. Day: Close stomata to conserve water and enter C3 Pathwayg. Must have cells with bothi. Large vacuoles to store malic acidii. Chloroplastsh. Water use efficiency can be greater than C4 or C3i. More widespread than C4j. 23 families of angiosperms mostly eudicotsXIV. Carbon fixation reactionsa. C4 more sensitive to cold than C3b. C3 more sensitive to cold than C4 or CAMc. CAM plants grow slowly, compete poorly in non-arid environmentsi. Ability to take in and fix Carbon limited by daytime stomata closureii. May close stomata continuously during droughtd.e.f. In secondary xylem (And secondary phloem)g. Visibilityi. Early wood less dense wider cells, thinner walls compared to late woodXV. Annual Ringsa. Growth ring represents one seasonXVI. False Annual ringsa. Change in water availability/environment produces more than one growth ring a yearXVII. Sapwooda. Light colored conductive woodXVIII. Heartwooda. Dark, nonconductive wood filled with oils, gums, resins, tannins (center ofthe stem)XIX. Overview of Glucose oxidationa. Breakdown of carbohydrates to generate energy to power the celli. Starch or sucrose must be broken down to sucrose firstii. ATP is producedb. Glucose loses electrons (And its H+ ions)c. Oxygen gains electrons (Reduced)d. C6H12O6 +6O2 6CO2 +6H2O +Energye. Does glucose oxidation require oxygen?i. Noii. Both Aerobic (more efficient) and nonaerobic pathway existsf. Four Stagesi. Glycolysisii. Citric Acid Cycleiii. Electron Transport Chainiv. Oxidative phosphorylationg. Energy converted to?i. ATPii. HeatXX. Glycolysisa. Ten steps, each catalyzed by specific enzymeb. Requires oxygen?i. Noii. Occurs in almost all living cells (cytosol)iii. Primitive process-occurred before O2 wasc. Yields two ATP, 2 pyruvate in atm; 2 NADHXXI. Aerobic Pathwaya. Key role of pyruvatei. If O2 is present, oxidized completely to CO2ii. If not, aerobic pathway less efficientb. Mitochondrial structurei. Cristae1. Citric acid cycle enzymes, ETC components2. Matrixa. Watery fluid in membranei. Other citric acid cycle enzymesXXII. Aerobic Pathwaya. Pyruvate enters matrixi. Then oxidized, and de-carboxylated (CO2 splits off)ii. NADH produced (electron carrier) b. Coenzyme Ai. Temporarily attached to acetyl group to become acetyl coAc. Citric acid cycle (aka Krebs Cycle)i. Begins with Acetyl co-Aii. Many
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