BBMB 405 1st Edition Lecture 3Outline of Last Lecture V. Summary of PhotosynthesisVI. Chapter 19: Light Reactions of PhotosynthesisA. Photosynthesis takes place in chloroplastB. Light absorption by chlorophyll induces electron transferC. Two photosystems generate a proton gradient and NADPH in oxygenic photosynthesisD. A proton gradient across the thylakoid membrane drives ATP synthesisE. Accessory pigments funnel energy into reaction centersF. The ability to convert light into chemical energy is ancientOutline of Current Lecture VII. HandoutA. Four light driven changes in stroma of chloroplasts (integration of light reactions with dark reactions)B. Crassulacean acid metabolism (CAM) plants (desert plants)C. DiagramVIII. Quiz 1 Answers (What I got)IX. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayA. Calvin cycle synthesizes hexoses from carbon dioxide and waterB. The activity of Calvin cycle depends on environmental conditionsX. NExtCurrent LectureThese 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. HandoutA. Four light driven changes in stroma of chloroplasts (integration of light reactions with dark reactions)1. Increased pH (protons pumped into thylakoid lumen), promotes carbamate formation on lysine of Rubisco2. Increased [Mg++] (transfer from thylakoid lumen to stroma), promotes formation of magnesium carbamate3. Increased NADPH/NADP+ (product of light reactions), activates phosphoribulose kinase (Ru-5-P  Ru-1,5-BP) and GAP dehydrogenase (1,3-PGA  GAP)4. Increased ferrodoxinred/ferrodoxinox (product of light reactions), reduces thioredoxin that then activates Rubisco5. Net effect: activation of rate-controlling reaction of Calvin cycleB. Crassulacean acid metabolism (CAM) plants (desert plants)1. Close stomata during day (conserve H2O) and open at night2. Absorb CO2 at night3. Store CO2 as malate (Starch  PEP  OAA  Malate) during night4. During day: Malate  Pyr + CO2 5. Net result: Photosynthesis without water lossC. DiagramD. VIII. Quiz I Answer (what I got)A. Write complete reaction of Calvin cycle that shows use of reduced product of PS-I(Photosystem I): reduced products of PS-I are NADPH and ATPB. Write complete reaction that shows use of high energy product of PS-1. I believethis question is the same as question A. High energy products are ATP and NADPH.C.14CO2 is incubated with chloroplasts with active Calvin cycle. Draw structure of first radioactive product generated by CO2 fixation reaction, showing position of 14C. A. Process of carbon dioxide fixation (below), radioactive structure should be unstable intermediate, isotope carbon should be pink one in structureD. Photorespiration results when rubisco functions as oxygenase rather than as carboxylase. Write specific reaction of photorespiration that shows consumption of oxygen.E. State specific role of reduced thioredoxin in regulation of Calvin cycle.A. Activates certain Calvin cycle enzymesB. Page 598: “Reduced form of thioredoxin activates many biosynthetic enzymesby reducing disulfide bridges that control their activity and inhibits several degradative enzymes.”IX. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayA. Calvin cycle synthesizes hexoses from carbon dioxide and water1. Introductiona. Calvin cycle is used by photosynthetic organisms to synthesize glucose form carbon dioxide (autotrophic)b. Three stages: i) fixation of CO2 by ribulose 1,5-bisphosphate for form two molecules of 3-phosphoglycerate ii) reduction of 3-phosphoglycerate to form hexose sugar iii) regeneration of ribulose 1,5-bisphosphate so that more CO2 can be fixed2. Carbon dioxide reacts with ribulose 1,5-bisphosphate to form two molecules of 3-phosphoglyceratea. Fixation of CO2b. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco)i. On stromal surface of thylakoid membraneii. Rate limiting step of hexose synthesisiii. Slow enzymeiv. Depends on Mg++ and carbamate for activity3. Rubisco activity depends on magnesium and carbamatea. Requires bound metal ion which serves to activate bound substrate molecule by stabilizing negative chargeb. CO2 molecule is required to complete Mg2+ binding site in rubisco by forming a carbamate4. Rubisco also catalyzes a wasteful oxygenase reaction: catalytic imperfectiona. When reactive intermediate reacts with O2 instead of CO2; because carbamate forms only by using CO2 rubisco is unable to catalyze oxygenase reaction exclusively when CO2 is absentb. Photorespiration: O2 is consumed and CO2 is release, not production of energy metabolite, used to covert phosphoglycolate into something useful (able to recycle 3-phosphoglycerate)5. Hexose phosphates are made from phosphglycerate and ribulose 1,5- bisphosphate is regenerateda. Reactions in hexose monophosphate pool and reactions catalyzed by rubisco convert CO2 to hexose, convert CO2 into chemical fuel at expense of ATP and NADPH generated from light reactionsb. Third step of Calvin cycle: regeneration of ribulose 1,5-bisphosphatei. Transketolase: transfer two carbon unit from ketone to aldoseii. Aldolase: catalyzes aldol condensation between dihydroxyacetone phosphate (DHAP) and aldehydeiii. Final step (note enzyme)iv. Overall reactionc. Calvin Cycle6. Three ATP and two NADPH molecules are used to bring carbon dioxide to level of hexose: net reaction of Calvin cycle:7. Starch and sucrose are major carbohydrate stores in plantsa. Store energy in forms of sugar: starch and sucroseb. Starch: polymer of ADP-glucose, synthesized and stored in chloroplastc. Sucrose: synthesized in cytoplasm because plants lack ability to transport hexose phosphates across chloroplast membrane so convert to triose phosphatesB. The activity of Calvin cycle depends on environmental conditions1. Introductiona. Light reactions work with dark reactions to regulate CO2 fixation by alteration of stromal environment by light reactionsb. Light reactions increase pH and stromal concentrations of Mg2+, NADPH, and reduced ferredoxin which play a role in activation of Calvin cycle enzymesc.2. Rubisco is activated by light-driven changes in proton and magnesium concentrationsa. Rubisco activity increases because light leads to carbamate formation necessary to enzyme activityb. pH increases and level of Mg2+ increases, Mg2+ ions from thylakoid space release into stroma compensate for influx of protons, carbamate formation is