Transcript Document
Forms of stored energy in cells Electrochemical gradients Covalent bonds (ATP) Reducing power (NADH) During photosynthesis, respiration and glycolysis these forms of energy are converted from one to another How is H+ EC gradient generated? Photosynthesis and Respiration generate EC gradients used to make ATP Glycolysis and food Complementary processes Autotroph Hetrotroph Autotroph Fig. 3-10 Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Electron transport chain Dark reactions Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain Chloroplast - plants and algae (in plasma membrane and cytoplasm of bacteria) ECB 14-30 Photosynthesis occurs in two stages (plants, algae, cyanobacteria) ‘Light’ reactions = photosynthetic e- transfer Occur in thylakoid membrane ‘Dark’ reactions = carbon fixation reactions Carbon fixation - bonding CO2 into organic molecules H+ EC gradient ECB 14-32 Light reactions - overview Proton gradient generated using energy from sunlight and e- transport chain Make ATP using F1F0 ATP synthase powered by a proton gradient H2O split to form O2 NADP+ reduced to NADPH by e- from e- transport chain Absorption spectra of pigments in plants Chlorophyll absorbs specific wavelengths of light; not all light is effective Chlorophyll Structure Conjugated double bonds stabilize excited electron Uses energy of an excited electron for: Tail allows chlorophyll to insert in membrane ECB 14-33 Antenna complex Resonance energy transfer 2H2O O2 + 4 H+ chlorophyll Reaction center - site of charge separation ECB 14-34 Charge separation at reaction center Takes 10-6 sec to complete! Donation of high energy e- to eFrom last slide transport chain ECB 14-35 Ends at resting state Charge Separation Summary P Q Chlorophyll in a special environment that allows for charge separation Primary electron acceptor Absorbtion of a photon e(From H2O) P Q Ground state P* Q First excited state P+ Q- Primary charge separation P Q e- Ground state Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Electron transport chain Dark reactions Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain High energy e- is donated to etransport chain ECB 4-36 Photosynthetic e- transport is vectorial ACIDIC and + charge 4 4 2 Splitting of water leaves H+ in thylakoid space B6/f complex e- to plastocyanin moves H+ from stroma to thylakoid space e- to FNR reduces NADP in stroma, consumes H+ in stromal Net result is synthesis of NADPH and generation of H+ EC gradient Electron Transport Chain Moves H+ Across membrane High energy electron Moves a high-energy electron through a sequence of electron carriers A carries (transmembrane proteins). electrons Each step electron loses energy directional sequence of carriers. Some carrier only only accept electrons, and other require a H+ to accompany the electron B carries electron plus H+ Low energy electron Proton movement across membrane C only carries electrons ECB 14-19 H+ transport involves conformational changes in protein e- energy drop Z scheme of electron transport - energy High energy edonated to etransport chain Energy of electron Small E steps NADP+ is terminal eacceptor Antenna complex ECB 14-37 Takes 2 photon to move 1 e- from H2O to NADP+ NADPH (H+ + 2e-) Reduction occurs in stroma ECB 3-35 EC gradient used to synthesize ATP Summary of light reactions in plants, algae and cyanobactia 14.6-light_harvesting.mov Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Electron transport chain Dark reactions Mitochondria structure Respiration - Mitochondrial electron transport Electron transport chain CO2 fixation Enzyme - ribulose bisphosphate carboxylase Carbon fixation - dark reactions Consume ATP and NADPH Bonds CO2 into organic molecules CO2 fixation phosphorylation Net 3 CO2 converted to a 3C organic molecule reduction Fate of gylceraldehyde 3 phosphate Enters glycolysis - next lecture Converted to sugars and starch in stroma and stored Starch can be converted back to sucrose and transported throughout plant to maintain energy needs (night) Chemiosmotic coupling is an ancient process Methanococcus- ancient archeabacterium thought to be primitive Generates H+ EC used to synthesize ATP - chemiosmotic coupling ECB 14-45 Evolution of photosynthesis Green sulfer bacteria use H2S as an e- donor and produce NADPH, (no ATP) Like photosystem I Photosynthesis allowed respiration to evolve Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Electron transport chain Dark reactions Evolution of photosynthesis Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain Photosynthesis and Respiration Glycolysis and food Complementary processes Autotroph Hetrotroph Autotroph Fig. 3-10 Where in the cell is ATP made? 1. Bacterial plasma membrane 2. Mitochondrial inner membrane 3. Chloroplast thylakoid membrane Respiration and Oxidative Phosphorylation bacteria mitochondria Photosynthesis chloroplasts ATP ADP + Pi Respiration in mitochondrion generates H+ EC gradient and ATP Mitochondrion and chloroplast have similar structures due to prokaryotic origins Extra membrane systemthylakoid membranes Overview of mitochondrial e- transport NADH ECB 14-13 Terminal e- acceptor is O2 (oxidative) Inside-out from photosynthesis in chloroplast NADH donates high energy e- *e- transport moves H+ outward *H+ flow inward generates ATP - oxidative phosphorylation NADH donates e- to electron transport chain H+ moved out across inner mito membrane at 3 steps 4 4 2 2 2 2 10 H+ pumped out per NADH oxidized Electrons are passed down energy gradient High energy e- donor is NADH Largest E steps Linked to H+ transport e- acceptor is oxygen FADH2 donates lower energy eFADH2 4 4 2 e- 2 2 2 2 6 H+ pumped out per FADH2 oxidized FADH2 Structure Flavin Adenine Dinucleotide Cytochrome oxidase consumers almost all the oxygen we breath Energy conversions in respiration H+ EC gradient Reducing power in NADH used to generate H+ EC gradient which drives ATP synthesis H+ flow inward generates ATP - oxidative phosphorylation ATP must is then transported out of mitochondrion Evolution of oxidative phosphorylation ATP synthase generating H+ EC gradient to drive membrane transport Electron transport chain to generate H+ EC gradient Coupling of e- transport chain to ATP synthesis (synthase reversed) ECB 14-41 Next topic Where do NADH and FADH2 come from? Answer - Glycolysis and Krebs cycle (Recall that during photosynthesis, NADPH is made in light reactions and used in dark reactions)