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 Autotroph Complementary processes Fig. 3-10 Autotroph Hetrotroph Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Dark reactions Respiration - Mitochondrial electron transport Mitochondria structure 1
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 H+ EC gradient Carbon fixation - bonding CO into organic molecules ECB 14-3 Light reactions - overview Proton gradient generated using energy from sunlight and e- transport chain Make ATP using F 1 F 0 ATP synthase powered by a proton gradient H O split to form O 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 H O O + 4 H + chlorophyll Reaction center - site of charge separation ECB 14-34 3
Charge separation at reaction center Takes 10-6 sec to complete! Donation of high energy e- to e- transport chain From last slide 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 H O) P Q Ground state P* Q First excited state P + Q - Primary charge separation e- P Q Ground state 4
Lecture 7 Photosynthesis Overview Light reactions Excitation of electrons Dark reactions Respiration - Mitochondrial electron transport Mitochondria structure High energy e- is donated to e- transport chain ECB 4-36 Photosynthetic e- transport is vectorial ACIDIC and + charge 4 4 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 5
Electron Transport Chain Moves H + Across membrane Moves a high-energy electron through a sequence of electron carriers (transmembrane proteins). Each step electron loses energy - directional sequence of carriers. Some carrier only only accept electrons, and other require a H + to accompany the electron Low energy electron High energy electron A carries electrons B carries electron plus H + 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 e- donated to e- transport chain Energy of electron Small E steps NADP + is terminal e- acceptor Antenna complex Takes photon to move 1 e- from H O to NADP+ ECB 14-37 6
NADPH (H + + e - ) 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 Dark reactions Respiration - Mitochondrial electron transport Mitochondria structure 7
CO fixation Enzyme - ribulose bisphosphate carboxylase Carbon fixation - dark reactions Consume ATP and NADPH Bonds CO into organic molecules CO fixation phosphorylation Net 3 CO 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) 8
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 H S as an e- donor and produce NADPH, (no ATP) Like photosystem I Photosynthesis allowed respiration to evolve 9
Photosynthesis Overview Light reactions Lecture 7 Excitation of electrons Dark reactions Evolution of photosynthesis Respiration - Mitochondrial electron transport Mitochondria structure Photosynthesis and Respiration Glycolysis and food Autotroph Complementary processes Fig. 3-10 Autotroph Hetrotroph Where in the cell is ATP made? 1. Bacterial plasma membrane. Mitochondrial inner membrane 3. Chloroplast thylakoid membrane Respiration and Oxidative Phosphorylation bacteria mitochondria Photosynthesis chloroplasts ATP ADP + P i 10
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 O (oxidative) Inside-out from photosynthesis in chloroplast *e- transport moves H + outward *H + flow inward generates ATP - oxidative phosphorylation NADH donates high energy e- NADH donates e- to electron transport chain 11
H+ moved out across inner mito membrane at 3 steps 4 4 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 FADH donates lower energy e- FADH 4 e - 4 6 H + pumped out per FADH oxidized 1
FADH 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 13
Evolution of oxidative phosphorylation ATP synthase generating H + EC gradient to drive membrane transport to generate H+ EC gradient ECB 14-41 Coupling of e- transport chain to ATP synthesis (synthase reversed) Next topic - Where do NADH and FADH come from? Answer - Glycolysis and Krebs cycle (Recall that during photosynthesis, NADPH is made in light reactions and used in dark reactions) 14