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How Cells Acquire Energy

Photosynthesis: The Big Picture. Source of BOTH matter and energy for most living organismsCaptures light energy from the sun and converts it into chemical energySynthesized organic molecules from inorganic moleculeBOTTOM LINE: Makes FOOD. Autotroph:Organisms that make their own food (energy-rich organic molecules) from simple, inorganic moleculesPhotoautotroph:Organisms that make their own food through photosynthesis; obtain energy from the sunType of autotrophHeterotroph:Get carbon a9459

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How Cells Acquire Energy

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    1. How Cells Acquire Energy Chapter 7

    2. Photosynthesis: The Big Picture Source of BOTH matter and energy for most living organisms Captures light energy from the sun and converts it into chemical energy Synthesized organic molecules from inorganic molecule BOTTOM LINE: Makes FOOD

    3. Autotroph: Organisms that make their own food (energy-rich organic molecules) from simple, inorganic molecules Photoautotroph: Organisms that make their own food through photosynthesis; obtain energy from the sun Type of autotroph Heterotroph: Get carbon and energy by eating autotrophs or one another Definitions

    4. Photoautotrophs Capture sunlight energy and use it to carry out photosynthesis Plants Some bacteria cyanobacteria Many protistans algae

    5. Linked Processes Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide

    6. Photosynthesis Equation

    7. Where Atoms End Up

    8. Chloroplast Structure

    9. Light dependent reactions Converts light energy into chemical energy (ADP? ATP) Gathers e- and H+ from water (NADP+ ? NADPH) Occurs in thylakoid membranes Light independent reactions (Calvin-Benson Cycle) Reduces CO2 to synthesize glucose using energy and hydrogens (i.e. ATP and NADPH) generated in the light dependent reaction Occurs in Stroma Notice that these reactions do not create NADH, but rather NADPH Two Stages of Photosynthesis

    10. Two Stages of Photosynthesis

    11. Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves Longest Radio waves wavelength

    12. Visible Light Electromagnetic energy with a wavelength of 308-750nm Light energy is organized into packets called photons The shorter the wavelength the greater the energy carried by the photons

    13. Properties of Light White light (from the sun) contains all of the wavelengths of light When light hits matter, it can be reflected (transmitted) or absorbed White substances reflect all light Black substances absorb all light

    14. Pigments A substance that absorbs light We see the color that is transmitted by pigment The absorbed color disappears into pigment

    15. Plant pigments Plant use a variety of pigments during photosynthesis: Chlorophylls a and b Carotenoids Anthocyanins Phycobilins The main photosynthetic pigment is Chlorophyll a

    16. Chlorophylls Chlorophyll a absorbs red and blue light, and reflects green light (what we see) Note: The colors that are absorbed are used for photosynthesis

    17. Effect of Light on Pigments What happens when light hits pigments? The color disappears, but the energy does not Absorbing photons of light excites electrons (e-), thus adding potential energy Ground state: normal pigment Excited state: pigment absorbing light (e- excited)

    18. Photosystems In thylakoid membrane, pigments are organized in clusters called photosystems These clusters contain several hundred pigment molecules Two types of photosystems Photosystem I = P700 (absorbs light at 700nm) Photosystem II = P680 (absorbs light at 680nm)

    19. Reaction Center Chlorophyll One of the pigments in each photosystem is known as the reaction center chlorophyll (RCC) if any pigment within the photosystem gets hit by a photon, the energy is transferred to the RCC The RCC will then transfer its excited e- into an electron transport chain

    20. Pigments in a Photosystem

    21. Light Dependent Reactions Location: the thylakoid membranes Function: to generate ATP (energy!) and NADPH (reducing power!) that will be used in the light independent reaction Two processes: Non-cyclic electron flow Generates ATP and NADPH Cyclic electron flow Generates only ATP

    22. Noncyclic Electron Flow Two-step pathway for light absorption and electron excitation Uses two photosystems: type I and type II Produces ATP and NADPH Involves photolysis - splitting of water

    23. Machinery of Noncyclic Electron Flow

    24. Steps of Non-cyclic electron flow Photosystem II gets hit by a photon; electron of RCC gets excited The excited (high energy) e- gets picked up by an electron carrier and taken into an electron transfer chain (ETC) The excited e- provides energy to pump protons (H+) into the thylakoid (tiny space) Through chemiosmosis, ATP is generated

    25. Chemiosmotic Model of ATP Formation Electrical and H+ concentration gradients are created between thylakoid compartment and stroma H+ flow down gradients into stroma through ATP synthase The energy driven by the flow of H+ powers the formation of ATP from ADP and Pi

    26. Chemiosmotic Model for ATP Formation

    27. Non-cyclic electron flow: Photolysis While Photosystem II gets hit by light, etc., water is split: H2O ? ˝ O2 + 2H+ + 2e- This process is called photolysis The H+ are pumped into the thylakoid to create the proton gradient The e- replace the excited e- that was taken away from the RCC

    28. Non-Cyclic Electron Flow: The saga continues Photosystem I gets excited at the same time as photosystem II Its excited e- gets taken into a second electron transfer chain that attaches the excited e- and the leftover H+ to NADP+ to make NADPH: NADP+ + H+ + e- ? NADPH

    29. Non-cyclic electron flow The “electron hole” in photosystem I is then filled with the used up, low energy e- from photosystem II Now everything is back to normal, and we can start all over again

    30. Energy Changes in Non-cyclic electron flow

    31. Non-cyclic electron flow: Summary After two excited photosystems, two ETCs and the splitting of water, both ATP and NADPH are generated!!!

    32. Cyclic electron flow The light independent reactions require more ATP than NADPH Cyclic electron flow is like a short cut to making extra ATP Involves only Photosystem I

    33. Cyclic electron flow Photosystem I gets excited Excited e- is carried into the first ETC; energy goes to pump H+ into thylakoid compartment Chemiosmosis powers formation of ATP The same e- (now low energy) replaces itself in the “electron hole” in Photosystem I

    34. Cyclic electron flow

    35. Light dependent reactions: Summary Non-cyclic electron flow Generates ATP

    36. Synthesis part of photosynthesis Can proceed in the dark Take place in the stroma Calvin-Benson cycle Light-Independent Reactions

    37. Calvin-Benson Cycle Overall reactants Carbon dioxide ATP NADPH Overall products Glucose ADP NADP+

    38. Calvin- Benson Cycle Three Phases: Carbon Fixation Reduction Regeneration of RUBP

    39. Calvin-Benson Cycle: Carbon Fixation Capturing atmospheric (gaseous) CO2 by attaching it to RuBP, a 5-carbon organic molecule This process forms two 3-carbon molecules The enzyme that catalyzes this process is called Rubisco

    40. Calvin Benson Cycle: Reduction The captured CO2 has very little energy and no hydrogens In order to make sugar, energy and hydrogens need to be added to the molecules formed by Carbon fixation ATP and NADPH (made in the light dependent reactions) break down to form ADP and NADP+ and, in the process, transfer energy and hydrogens to the 3-carbon compounds formed by carbon fixation, resulting in sugar formation

    41. Calvin-Benson Cycle: Regeneration Some of the sugar created by reduction leaves the Calvin cycle, and is used to build up glucose and other organic molecules The rest of the sugar is used to remake (regenerate) RuBP This process requires ATP (which was made in the light dependent reactions)

    42. Calvin-Benson Cycle: Summary The cycle proceeds 6 times to form each molecule of glucose In the process, ATP and NADPH is used up 6CO2 are converted into C6H12O6 - glucose

    43. In Calvin-Benson cycle, as described, the first stable intermediate is a three-carbon PGA Because the first intermediate has three carbons, the pathway is called the C3 pathway The C3 Pathway

    44. Photorespiration in C3 Plants On hot, dry days stomata (holes in the leaf) close to prevent evaporation of water As a result, within the leaf oxygen levels rise, and Carbon dioxide levels drop Rubisco attaches RuBP to oxygen instead of carbon dioxide Results in a VERY wasteful process known as Photorespiration – uses up ATP without generating sugar

    45. C4 and CAM Plants To avoid photorespiration, plants that live in hot, dry climates evolved mechanisms to separate carbon fixation from the Calvin Cycle The CO2 that enters the Calvin cycle is derived from the breakdown of previously synthesized organic acids In this way, the enzyme that catalyzes the reaction that attaches CO2 to RuBP is not exposed to atmospheric oxygen

    46. C4 and CAM Plants C4 plants do carbon fixation in a different location (cell type) than the Clavin cycle CAM plants do carbon fixation at a different time (night) that the Calvin cycle (day)

    47. Summary of Photosynthesis

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