Photosynthesis - Hemsley - 2024 PDF

Oxygenic photosynthesis Dr. Piers Hemsley [email protected] [email protected] @Hemsley_lab Photosynthesis summary Conversion of light energy into chemical energy and reducing power Chemiosmosis used to make ATP NADP+ reductase forms NA...

Oxygenic photosynthesis Dr. Piers Hemsley [email protected] [email protected] @Hemsley_lab Photosynthesis summary Conversion of light energy into chemical energy and reducing power Chemiosmosis used to make ATP NADP+ reductase forms NADPH  Recommended textbook Smith, & Smith, A. M. (Alison M. 2010). Plant biology. Garland Science. ISBN : 9780815340256 Main Library 3 copies available General Shelving ; 580 P 713 https://dundee.primo.exlibrisgroup.com/permalink/44DUN_INST/s4l06a/alma99001096800030 2991  Photosynthesis learning objectives Understand photosynthetic use of different wavelengths of light. Knowledge of chloroplast structure Detailed knowledge of the structure, function and molecular mechanism of photosystems I and II Förster resonant energy transfer Conversion of light into chemical energy through charge separation Generation of H+ gradient Electron transport Understanding of how some herbicides target photosynthesis Understanding of how chloroplasts cope with environmental change  What has photosynthesis ever done for us? oxygen in atmosphere / % 20 is es th 10 yn os is ot ed es ph th rm yn c fo ni os h ge fe rt ot xy Ea Li Ph O 0 5 4 3 2 1 0 time / billions of years ago What has photosynthesis ever done for us?  oxygen in atmosphere / % 0 10 20 us? 5 Ea rt h fo rm ed 4 Li fe Ph ot os yn 3 O th xy es ge is ni c ph ot Ae os yn ro 2 bi th c es is M re s en ito pi Pdho ch ra o eu osty n tion time / billions of years ago ka oms dri ry ybnio al ot thsi 1 es est ic La What has photosynthesis ever done for nd pl a nt s 0 Cyanobacteria and chloroplasts Cyanobacteria and chloroplasts  The structure of a chloroplast Stromal thylakoid Granal thylakoid Stroma Lumen Granal stack Outer envelope (bilayer) Inner envelope (bilayer) The structure of a thylakoid NADP+ NADPH ATP ADP 4 e- 4H + FD 8 H+ Chloroplast Cyt b6f stroma P680 PQ P700 4 e- 4e - 4 e- PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Thylakoid lumen Why are chloroplasts green?  Photosynthetically active radiation relative absorbance Action spectrum wavelength / nm Photosynthesis summary Conversion of light energy into chemical energy and reducing power Chemiosmosis – ATP NADP+ reductase – NADPH  Photosynthesis summary 1 1. Excitation of antenna Physica chlorophyll l 2 2. Transfer of energy to reaction energy centre H2O 3. Primary charge separation 5 3 + event displaces electron _ O2 + H+ 4. ETC forms electrochemical gradient to drive ATP synthesis Chemic NADP+ ADP and form NADPH al 4 5. H2O oxidised to replenish energy NADPH ATP reaction centre electron CO2 Calvin cycle  Chlorophyll methyl aldehyde reduced pyrrole ring lipophilic isoprenoid chain Chlorophyll a Chlorophyll b Structure of a photosystem light harvesting complex b>a b>a Chlorophyll b b>a Amax ~ 650 nm energy after excitation b>a a>b a>b b>a a>b b>a Chlorophyll a a>b a Amax ~ 670 nm b>a a>b b>a a>b b>a RC Chlorophyll a b>a core complex Amax ~ 680 nm (PSII) b>a b>a Amax ~ 700 nm (PSI) Light harvesting complex a a b b b a b a b b a a Accessory pigments enhance light harvesting capabilities  Chlorophyll energy transfer A655 A650 A670 A660 A665 Förster resonant energy transfer Chem. Rev. 2017, 117, 2, 249–293 Photosystems, ETC and ATP synthesis ? NADPH ATP  Photosystems, ETC and ATP synthesis CO2 Calvin cycle Stroma NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- 4 e- PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Thylakoid lumen  The Z-scheme Excited (reduced) P700* 2 e- NADPH PSII can’t reduce NADP+ Charge separation NADP+ reducing potential P680* 2 e- PQ/b6f/PC P700 Charge separation H 2O 2 e- (oxidised) PSI P680 can’t oxidise ½ O2 H 2O PSII PSI Photosystems, ETC and ATP synthesis CO2 Calvin cycle NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- 4 e- PC 2 H 2O O2 + 4H+ 4 H+ Photosystem II Photosystem I Photosystem II – Oxygen producing 4 H+ Fe2+ PQ PQ A B 4e - PQEx Phe B o Chl P680 4 e- D2 D1 Mn Mn 4 H+ 4 e- Mn Mn 2H2O O2 + 4H+ Photosystems, ETC and ATP synthesis CO2 Calvin cycle NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- 4 e- PC 2 H2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Photosystem I – NADPH producing 4 e- 2 NADP+ FD-NADP Fd reductase Fe 2 NADPH S Fe S Fe PQ S PQ 2 e- 2 e- Chl P700 PsaA 4 e- PsaB PC  Photosynthesis and the environment Day Night Cloud cover Canopy cover High exposure  Too much light! - PSII Rate limiting – particularly in high light and low temperatu Stroma NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- 4 e- PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II H+ H+ H+ H+Photosystem I H+ H+ H + H + + Thylakoid lumen H  Too much light - non-photochemical quenching Rate limiting – particularly in high light and low temperatu Stroma NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- Heat PC Zeaxanthin VDE Violaxanthin Monodehydro Ascorbate ascorbate H+ H+ H+ H+ Low pH H VDE recruitment H + H + H + + H+  Too much light! - PSI Rate limiting – particularly in high light and low temperatu Stroma NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f e- P680 PQ eP700 - e- e- 4 e- 4 e- e-e - PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Thylakoid lumen  Too much light – the water-water cycle 2 H 2O H2O2 + O2 APX Monodehydro AscorbateSOD Stroma ascorbate 2 H+ ATP ADP MDAR DASAR O2 O2._ e - e - e- e- 4 H+ 8 H+ Cyt b6f e- P680 PQ eP700 - e- e- 4 e- 4 e- e-e - PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Thylakoid lumen Herbicides Erin Burns, MSU  Herbicide action Atrazine t main effects of herbicides are through PSII mediated ROS generation…  Cyclic photosynthesis Stroma NADP+ NADPH ATP ADP 4 e- 4 H+ FD 8 H+ Cyt b6f P680 PQ P700 4 e- 4 e- 4 e- PC 2 H 2O O2 + 4 H+ 4 H+ Photosystem II Photosystem I Thylakoid lumen  Cyclic photosynthesis sed by Purple and Green phototrophic bacteria, but also plants under str xternal electron donor required (e.g. H2S, succinate) if NADPH is to be m Stroma NADP+ NADPH ATP ADP H+ H+ e- FD H+ e - e - Cyt b6f e- NDH PQ PXXX complex PGR5 4 e- PC H+ H+ Photosystem I Thylakoid lumen Comparison with aerobic respiration Photosynthesis H 2O Light + CO2 Triose phosphate O2 Respiration O2 Pyruvate CO2 + ATP H 2O Summary Photosynthesis converts light to chemical energy. ATP is generated by chemiosmosis using a proton gradient formed by light induced electron transfer. Two distinct linked light harvesting systems are required to provide sufficient energy to use electrons from water to reduce NADP + to NADPH.  Further reading Additional topics Why is there only one electron path in PSII? Cyclic photosynthesis (e.g. purple bacteria) Organisation and regulation of PSI and PSII in thylakoid membranes (“state transitions”) What happens to absorbed blue light? Why do different plants have different compensation points (photosynthesis > respiration) ? References Smith et al. Plant biology. Garland Science ISBN 978-0-8153-4025-6 Available in library Alberts et al., Molecular Biology of the Cell (6 th edition); Garland Science Stryer. Biochemisty (7th edition); Freeman  Gatsby Summer Studentships 10 week funding (£4700 stipend and expenses) Do a practical project anywhere in UK Highly prestigious Closing date ~20th Feb 2025 Past alumni: Jennie Yang (L4), Hazel Surtees (L4)