BBMB 405 1st Edition Lecture 3 Outline of Last Lecture V VI A B C D E F Summary of Photosynthesis Chapter 19 Light Reactions of Photosynthesis Photosynthesis takes place in chloroplast Light absorption by chlorophyll induces electron transfer Two photosystems generate a proton gradient and NADPH in oxygenic photosynthesis A proton gradient across the thylakoid membrane drives ATP synthesis Accessory pigments funnel energy into reaction centers The ability to convert light into chemical energy is ancient Outline of Current Lecture VII Handout A Four light driven changes in stroma of chloroplasts integration of light reactions with dark reactions B Crassulacean acid metabolism CAM plants desert plants C Diagram VIII Quiz 1 Answers What I got IX Chapter 20 The Calvin Cycle and the Pentose Phosphate Pathway A Calvin cycle synthesizes hexoses from carbon dioxide and water B The activity of Calvin cycle depends on environmental conditions X NExt Current Lecture 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 Handout A 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 Rubisco 2 Increased Mg transfer from thylakoid lumen to stroma promotes formation of magnesium carbamate 3 Increased NADPH NADP product of light reactions activates phosphoribulose kinase Ru 5 P Ru 1 5 BP and GAP dehydrogenase 1 3PGA GAP 4 Increased ferrodoxinred ferrodoxinox product of light reactions reduces thioredoxin that then activates Rubisco 5 Net effect activation of rate controlling reaction of Calvin cycle B Crassulacean acid metabolism CAM plants desert plants 1 Close stomata during day conserve H2O and open at night 2 Absorb CO2 at night 3 Store CO2 as malate Starch PEP OAA Malate during night 4 During day Malate Pyr CO2 5 Net result Photosynthesis without water loss C Diagram D 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 ATP B Write complete reaction that shows use of high energy product of PS 1 I believe this question is the same as question A High energy products are ATP and NADPH C 14 CO2 is incubated with chloroplasts with active Calvin cycle Draw structure of first radioactive product generated by CO2 fixation reaction showing position of 14 C A Process of carbon dioxide fixation below radioactive structure should be unstable intermediate isotope carbon should be pink one in structure D 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 enzymes B Page 598 Reduced form of thioredoxin activates many biosynthetic enzymes by reducing disulfide bridges that control their activity and inhibits several degradative enzymes IX Chapter 20 The Calvin Cycle and the Pentose Phosphate Pathway A Calvin cycle synthesizes hexoses from carbon dioxide and water 1 Introduction a 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 fixed 2 Carbon dioxide reacts with ribulose 1 5 bisphosphate to form two molecules of 3 phosphoglycerate a Fixation of CO2 b Ribulose 1 5 bisphosphate carboxylase oxygenase rubisco i On stromal surface of thylakoid membrane ii Rate limiting step of hexose synthesis iii Slow enzyme iv Depends on Mg and carbamate for activity 3 Rubisco activity depends on magnesium and carbamate a Requires bound metal ion which serves to activate bound substrate molecule by stabilizing negative charge b CO2 molecule is required to complete Mg2 binding site in rubisco by forming a carbamate 4 Rubisco also catalyzes a wasteful oxygenase reaction catalytic imperfection a 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 absent b 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 5bisphosphate is regenerated a 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 reactions b Third step of Calvin cycle regeneration of ribulose 1 5 bisphosphate i Transketolase transfer two carbon unit from ketone to aldose ii Aldolase catalyzes aldol condensation between dihydroxyacetone phosphate DHAP and aldehyde iii Final step note enzyme iv Overall reaction c Calvin Cycle 6 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 plants a Store energy in forms of sugar starch and sucrose b Starch polymer of ADP glucose synthesized and stored in chloroplast c Sucrose synthesized in cytoplasm because plants lack ability to transport hexose phosphates across chloroplast membrane so convert to triose phosphates B The activity of Calvin cycle depends on environmental conditions 1 Introduction a Light reactions work with dark reactions to regulate CO2 fixation by alteration of stromal environment by light reactions b Light reactions increase pH and stromal concentrations of Mg2 NADPH and reduced ferredoxin which play a role in activation of Calvin cycle enzymes c 2 Rubisco is activated by light driven changes in proton and magnesium concentrations a Rubisco activity increases because light leads to carbamate formation necessary to enzyme activity b pH increases and level of Mg2 increases Mg2 ions from thylakoid space release into stroma compensate for influx of protons carbamate formation is favored CO2 adds to deprotonation of rubisco Mg2 ions bind to cabamate to generate active enzyme 3 Thioredoxin plays key role in regulating Calvin