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Autotrophs Organisms capture and store free energy for use in biological processes Slide 2 Name to methods that autotrophs use to capture energy from physical sources in the environment. Photosynthetic Organisms capture free energy present in sunlight Plants, Algae, Cyanobacteria Chemosynthetic Organisms capture free energy from small inorganic molecules present in their environment, and this process can occur in the absences of oxygen Bacteria Slide 3 Chloroplasts The Structure and Function of Subcellular components, and their interactions, provide essential cellular processes Slide 4 How are chloroplasts specialized to capture energy for photosynthesis? Chloroplasts have a double outer membrane that creates a compartmentalized structure to support function Within the chloroplasts are membrane-bound structures called thylakoids Energy-capturing reactions housed in the thylakoids are organized in stacks, called grana to produce ATP and NADPH 2, which fuel carbon-fixing reactions in the Calvin Cycle Carbon fixation occurs in the stroma, where molecules of CO 2 are converted to carbohydrates Slide 5 Fig. 10-3b 1 m Thylakoid space Chloroplast Granum Intermembrane space Inner membrane Outer membrane Stroma Thylakoid Slide 6 Lighter Reactions of Photosynthesis Organisms capture and store free energy for use in biological processes Slide 7 What is the electron carrier/acceptor for photosynthesis? NADPH Slide 8 How does photosynthesis trap the energy from the sun to form ATP and NADPH? Chlorophyll reflects and transmits green light Chlorophyll absorbs energy in red and blue light When Chlorophyll absorbs free energy from light, the energy is used to boost electrons to a higher energy level in Photosystems I and II Reflected light Absorbed light Light Chloroplast Transmitted light Granum Slide 9 Does chlorophyll work alone? No it is aided by accessory pigments that absorb different wavelengths of light Chlorophyll a is the main photosynthetic pigment Chlorophyll b and carotenoids are accessory pigments that help the organism capture the maximum about of energy available Slide 10 Fig. 10-9 Wavelength of light (nm) (b) Action spectrum (a) Absorption spectra (c) Engelmanns experiment Aerobic bacteria Rate of photosynthesis (measured by O 2 release) Absorption of light by chloroplast pigments Filament of alga Chloro- phyll a Chlorophyll b Carotenoids 500 400 600700 600 500 400 Slide 11 Where are photosystems I and II? Photosystems I and II are embedded in the internal membranes of chloroplasts (in thylaykoids) and are connected by the transfer of higher free energy electrons through and electron transport chain. Photosystem II is located in from of photosystem I named by the order in which they were discovered. Photosystem I PSI or P700; absorbs light best at a wavelength of 700nm Photosystem II PSII or P680; absorbs light best at a wavelength of 680nm Slide 12 Fig. 10-12 THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA ee Pigment molecules Photon Transfer of energy Special pair of chlorophyll a molecules Thylakoid membrane Photosystem Primary electron acceptor Reaction-center complex Light-harvesting complexes Slide 13 What happens when light strikes chlorophyll a? When chlorophyll a absorbs light, its electrons go from a ground state to an excited state. Electrons at the excited state are passed onto the the primary electron acceptor within the reaction center of the photosystem The electrons are then passed between molecules as they move through the ETC. The movement of electrons creates an electrochemical gradient of H + across the thylakoid membrane Slide 14 What is the final acceptor of electrons in the Light Reactions of Photosynthesis? NADP + H + NADPH Pigment molecules Light P680 ee Primary acceptor 2 1 ee ee 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I ) Light Primary acceptor ee P700 6 Fd Electron transport chain NADP + reductase NADP + + H + NADPH 8 7 ee ee 6 Photosystem II (PS II ) Slide 15 How are electrons replaced at each photosystem? PSII / P680 A water molecules is split Electrons go to chlorophyll a H+ adds to electrochemical gradient across the thylakoid Oxygen atoms join to form Oxygen gas released into atmosphere thru stomata PSI / P700 Electrons from PSII flow thru ETC to PSI Slide 16 What happens with the elctrochemical gradient? Build up of H+ within the lumen of the thylakoid is used to create ATP by adding Pi to ADP H+ pass thru ATP synthase in the thylakoid as they move down the concentration gradient, energy is harnessed to phosphorylate ADP making ATP Slide 17 Fig. 10-17 Light Fd Cytochrome complex ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H + concentration) Thylakoid membrane THYLAKOID SPACE (high H + concentration) STROMA (low H + concentration) Photosystem II Photosystem I 4 H + Pq Pc Light NADP + reductase NADP + + H + NADPH +2 H + H2OH2O O2O2 ee ee 1/21/2 1 2 3 Slide 18 What are the products of the light reactions of photosynthesis NADPH and ATP are produced and used to power the production of carbohydrates in the Calvin Cycle Oxygen is released as a waste product (from the splitting of H 2 O) Slide 19 Do all photosynthetic autotrophs produce ATP to drive the Calvin cycle in a linear process (PSII to PSI)? No some organisms only have one photosystem (PSI) These organisms use cyclic electron flow Cyclic electron flow does not produce NADPH; it only produces ATP Some organisms can switch between linear and cyclic electron flow to supplement ATP production ATP Photosystem II Photosystem I Primary acceptor Pq Cytochrome complex Fd Pc Primary acceptor Fd NADP + reductase NADPH NADP + + H + Slide 20 Where did photosynthesis first evolve? Prokaryotic organisms Scientific evidence supports that prokaryotic photosynthesis was responsible for the production of an oxygenated atmosphere Prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis