Lec6-photosynthesis-slides.pdf

Photosynthesis & Plant Energetics Required Reading - TMMZ Chapter 9, sections 9.1-9.8 Chapter 10, section 10.1 2 biology4alevel.blogspot.com Overview of Metabolism (Adapted from Voet & Voet, Biochemistry, 2nd Ed; John Wiley & Sons, 1995) Photosynthesis: the most important biological process...

Photosynthesis & Plant Energetics Required Reading - TMMZ Chapter 9, sections 9.1-9.8 Chapter 10, section 10.1 2 biology4alevel.blogspot.com Overview of Metabolism (Adapted from Voet & Voet, Biochemistry, 2nd Ed; John Wiley & Sons, 1995) Photosynthesis: the most important biological process on earth Long, 2013 Two sets of reactions: • Thylakoid reactions (light-driven reactions) ▫ Uses water, produces oxygen ▫ Uses ADP, NADP+, produces ATP, NADPH ▫ Energy input from photons Can use O2 production to measure rate of photosynthesis • Carbon reactions (enzyme-driven reactions) ▫ Uses CO2, produces sugars ▫ Uses ATP, NADPH, produces ADP, NADP+ ▫ Energy input from lightdependent reactions Can use net CO2 consumption to measure rate of photosynthesis biology4alevel.blogspot.com 5 6 Light = Energy Waves Particles (photons) TMMZ Fig. 9.2 7 Pigments • Molecules that absorb photons ▫ Generally coloured (the reflected wavelengths) • Absorption of a photon increases the energy level of the molecule spectrum TMMZ Fig. 9.4 8 Absorption spectrum of a leaf Absorption spectrum of a leaf (or leaf pigment extract) Relative rate of photosynthesis TMMZ Fig. 9.8 9 Absorption spectra for a number of pigments TMMZ Fig. 9.7 Catching light: Energy from harvested photons is transferred to the reaction centre 10 Light harvesting complex (LHC) Photosystem TMMZ Fig. 9.10 11 Photosynthetic electron-transport chain Charge separation at PSII yields e- and oxidized P680* Oxygen evolving complex strips electrons from water, passes them to oxidized P680* Second charge separation at PSI yields e- and oxidized Electrons passed to strong P700 reductant (NADPH) Electrons “stored” in PQ-pool, transferred to oxidized P700 via PET Discovered second Discovered first TMMZ Fig. 9.12 12 Catching light: Chloroplast Architecture Thylakoid membranes: Light-dependent (thylakoid) reactions PSII in grana lamellae; PSI in stroma lamellae Stroma (fluid): Light-independent (carbonreduction) reactions TMMZ 9.14 Reducing potential transferred via Plastoquinone (PQ) and plastoquinol (PQH2) Ferredoxin complex reduces NADP+ H+ release generates a proton gradient Oxygen-evolving complex ... oxidises water 13 Protons drive ATP synthase Plastocyanin Transfers electrons to PSI TMMZ Fig. 9.19 What to do with the NADPH and ATP? The carbon fixation reactions TMMZ Fig. 10.1 14 15 The Calvin-Benson cycle (aka the photosynthetic carbon reduction cycle) Rubisco TMMZ Fig. 10.2 16 Rubisco Ribulose-1,5-bisphosphate carboxylase oxygenase • Fun facts: The most abundant protein on earth Contains 8 subunits (4 small, 4 large) Small subunit encoded in nuclear genome, large subunit in chloroplast genome 17 The Calvin-Benson cycle (aka the photosynthetic carbon reduction cycle) RuBP ATP from thylakoid (light) reactions TMMZ Fig. 10.2 Rubisco ATP & NADPH from thylakoid (light) reactions 18 (Carboxylation) GP aka 3-phosphoglycerate https://ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled-2/light-independent-reactions.html 19 GP aka 3-phosphoglycerate https://ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled-2/light-independent-reactions.html 20 GP aka 3-phosphoglycerate https://ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled-2/light-independent-reactions.html 21 What if the electron transport and CalvinBenson Cycle capacities are mismatched? Rates of production vs. use of reducing equivalents TMMZ Fig. 10.1 Fast, physical processes: largely temperatureindependent Enzyme-catalysed processes: quite temperature dependent Diffusion: a bit temperature-dependent TMMZ Fig. 9.19 22 23 Less temperature-dependent (Production of reducing equivalents) More temperature-dependent (Consumption of reducing equivalents) 24 • Calvin-Benson cycle slows down more than photosynthetic ETC • More reducing equivalents produced than consumed • Potential build-up of ROS etc. 25 • More reducing equivalents produced than consumed • Potential build-up of ROS etc. • Insufficient Pi available to generate ATP • Increase in output of ETC, no change in Calvin-Benson cycle... Repair and regulation 26 Non-photochemical quenching Xanthophyll cycle TMMZ Fig. 9.31 Rearrange LHC 27 Repair and regulation TMMZ Fig. 9.31