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?

Glycolysis and Photosynthesis and Respiration generate EC gradients used to make ATP food Complementary processes Fig Autotroph Hetrotroph

Light reactions Electron transport chain Dark reactions Overview Lecture 7 Photosynthesis Excitation of electrons 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 CO 2 into organic molecules ECB H+ EC gradient

Make ATP using F 1 F 0 ATP synthase powered by a proton gradient Light reactions - overview H 2 O split to form O 2 NADP + reduced to NADPH by e- from e- transport chain Proton gradient generated using energy from sunlight and e- transport chain

Chlorophyll absorbs specific wavelengths of light; not all light is effective Absorption spectra of pigments in plants

Uses energy of an excited electron for: Chlorophyll Structure Tail allows chlorophyll to insert in membrane Conjugated double bonds stabilize excited electron ECB 14-33

Antenna complex chlorophyll Resonance energy transfer Reaction center - site of charge separation 2H 2 O O H + ECB 14-34

Charge separation at reaction center Takes sec to complete!

Donation of high energy e- to e- transport chain From last slide Ends at resting state ECB 14-35

P Chlorophyll in a special environment that allows for charge separation Q Primary electron acceptor PQ Ground state Absorbtion of a photon P* Q First excited state P+P+P+P+ Q-Q-Q-Q- Primary charge separation e- e- PQ Ground state Charge Separation Summary (From H 2 O)

Lecture 7 Light reactions Electron transport chain Dark reactions Overview Photosynthesis Excitation of electrons Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain

High energy e- is donated to e- transport chain ECB 4-36

Photosynthetic e- transport is vectorial 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 ACIDIC and + charge

Moves a high-energy electron through a sequence of electron carriers (transmembrane proteins). Some carrier only only accept electrons, and other require a H + to accompany the electron Each step electron loses energy - directional sequence of carriers. A carries electrons High energy electron B carries electron plus H + C only carrieselectrons Low energy electron Protonmovementacrossmembrane Electron Transport Chain Moves H + Across membrane ECB 14-19

H+ transport involves conformational changes in protein e- energy drop

Z scheme of electron transport - energy Antenna complex High energy e- donated to e- transport chain NADP + is terminal e- acceptor Takes 2 photon to move 1 e- from H 2 O to NADP+ Small E steps ECB Energy of electron

NADPH (H + + 2e - ) ECB 3-35 Reduction occurs in stroma

Summary of light reactions in plants, algae and cyanobactia EC gradient used to synthesize ATP 14.6-light_harvesting.mov

Lecture 7 Light reactions Electron transport chain Dark reactions Overview Photosynthesis Excitation of electrons Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain

CO 2 fixation Enzyme - ribulose bisphosphate carboxylase

Carbon fixation - dark reactions Consume ATP and NADPH Bonds CO 2 into organic molecules CO 2 fixation phosphorylation reduction Net 3 CO 2 converted to a 3C organic molecule

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 H 2 S as an e- donor and produce NADPH, (no ATP) Like photosystem I

Photosynthesis allowed respiration to evolve

Lecture 7 Light reactions Electron transport chain Dark reactions Evolution of photosynthesis Overview Photosynthesis Excitation of electrons Respiration - Mitochondrial electron transport Mitochondria structure Electron transport chain

Photosynthesis and Respirationfood Complementary processes Fig Autotroph Hetrotroph Glycolysis and

Where in the cell is ATP made? 1. Bacterial plasma membrane 2. Mitochondrial inner membrane 3. Chloroplast thylakoid membrane ATP ADP + P i chloroplasts Photosynthesis bacteriamitochondria Respiration and Oxidative Phosphorylation

Respiration in mitochondrion generates H + EC gradient and ATP Mitochondrion and chloroplast have similar structures due to prokaryotic origins Extra membrane system- thylakoid membranes

Overview of mitochondrial e- transport Inside-out from photosynthesis in chloroplast ECB Terminal e - acceptor is O 2 (oxidative) *e- transport moves H + outward *H + flow inward generates ATP - oxidative phosphorylation NADH donates high energy e- NADH

NADH donates e- to electron transport chain

H+ moved out across inner mito membrane at 3 steps H + pumped out per NADH oxidized

High energy e - donor is NADH e - acceptor is oxygen Electrons are passed down energy gradient Largest E steps Linked to H + transport

FADH 2 donates lower energy e H + pumped out per FADH 2 oxidized FADH 2 2 e -

FADH 2 Structure Flavin Adenine Dinucleotide

Cytochrome oxidase consumers almost all the oxygen we breath

Energy conversions in respiration H + flow inward generates ATP - oxidative phosphorylation Reducing power in NADH used to generate H + EC gradient which drives ATP synthesis H+ EC gradient ATP must is then transported out of mitochondrion

Evolution of oxidative phosphorylation ATP synthase generating H + EC gradient to drive membrane transport ECB Electron transport chain to generate H+ EC gradient Coupling of e- transport chain to ATP synthesis (synthase reversed)

Next topic - Where do NADH and FADH 2 come from? Answer - Glycolysis and Krebs cycle (Recall that during photosynthesis, NADPH is made in light reactions and used in dark reactions)