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04a photosynthesis-2010 update stacy

04a photosynthesis-2010 update stacy






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  • - compare and contrast mitochondria and chloroplast structure
  • Q: What happens to electrons when light strikes them? A: Excited, gain energy, higher potential energy level - think of glow in the dark objects (the light we see is electrons falling back to ground state)
  • What is the primary light absorbing molecule in green plants? Why does it make plants appear green?
  • - compare and contrast mitochondria and chloroplast structure
  • lumen – inside grana stacks stroma – inside chloroplast Z enzyme – splits water to ½ O 2 and 2 H + photosystem II – aka P680 PQ – plastoquinone cytochrome complex PC – plastocyanin photosystem I – aka p700 Fd – ferrodoxin NADPH reductase – makes NADPH

04a photosynthesis-2010 update stacy 04a photosynthesis-2010 update stacy Presentation Transcript

  • Photosynthesis Overview
    • CO 2 + H 2 O C 6 H 12 O 6 + O 2
    • photosynthesis – creating using light
    • Only chloroplast organelles and special bacteria have the proteins necessary to carry out this function.
  • Photosynthesis: Two Major Processes
    • The Light Reactions
    • Carbon Fixation
    • harvest light energy to create ATP
    • Process of producing C 6 H 12 O 6 from CO 2 and H 2 O
  • Photosynthesis
  • Photosynthesis
  • Chloroplast Structure
  • The Light Reactions
    • Photoexcitation
    • Electron transport
    • Photophosphorylation (chemiosmosis)
    • Absorption of light photons
    • Similar to ETC in mitochondria
    • ATP synthesis due to electrochemical gradient
  • Photoexcitation
    • e - gain energy when atoms absorb energy.
    • e - fall back to lowest energy level ( ground state ) if it isn’t transferred to another molecule
  • Light Absorbing Pigments
    • chlorophyll – groups of light absorbing molecules in green plants
  • Chlorophyll Absorption Spectrum -Visible light drives photosynthesis. -the shorter the wavelength, the greater the energy of each photon of that light. Chlorophyll a – absorbs reds and blues for photosynthesis.
  • Other Light Absorbing Pigments
    • carotenoids – other pigment molecules that can collect light energy
  • Photosystems
    • chlorophyll and other light absorbing pigments in the thylakoid make up a photosystem protein
  • Photosystem Structure
    • reaction centre – chlorophyll a is located in the region of the photosystem called the reaction center.
    • -once chlorophyll a is excited by light, it loses an electron to the electron acceptor.
    • The electron acceptor traps the high energy electron before it returns back to ground state.
  • Photosystems
    • Two purposes:
      • to collect as much light energy as possible
      • excite chlorophyll a and transfer its electrons to an electron acceptor and through a series of proteins (electron transport)
  • Electron Transport
    • Electron transport occurs in the thylakoid membrane.
    • Two mechanisms of electron transport:
    • Non-cyclic electron flow
    • Cyclic electron flow
  • Thylakoid Membrane Proteins
  • Thylakoid Proteins: PSII
    • 2e - transferred from H 2 O to photosystem II ( PS II )
    • also known as P680 (maximum absorption at 680nm wavelength)
    • light energy is required to help create O 2
    • protons are released into the lumen
  • Thylakoid Proteins: Pq
    • e - transferred to plastiquinone (Pq) only when enough energy is collected by PSII
    • PQ is a mobile component within the thylakoid membrane
  • Thylakoid Proteins: Cytochrome Complex
    • e - transferred from PQ to cytochrome complex
    • protons pumped from stroma to lumen across thylakoid membrane
  • Chloroplast Structure
  • Thylakoid Proteins: Pc
    • e- transferred to plastocyanin (Pc)
    • PC is a movable component on thylakoid surface in lumen
  • Thylakoid Proteins: PSI
    • e- transferred to photosystem I (PSI)
    • also known as P700 (maximum 700 nm wavelength absorption)
  • Thylakoid Proteins: Fd
    • e - transferred to ferrodoxin (Fd) only when enough energy has been collected by PSI
    • movable component on thylakoid surface in stroma
  • Thylakoid Proteins: NADP + Reductase
    • e - transferred to NADP + reductase
    • final electron acceptor is NADP + that is reduced to NADPH
  • Thylakoid Proteins: ATP Synthase
    • protons pumped into the lumen pass through ATP synthase
    • ATP produced in stroma
    • photophosphorylation – light-dependent formation of ATP by chemiosmosis
  • Non-cyclic Electron Flow: Z-Scheme
  • Non-cyclic Electron Transfer Summary
    • H 2 O is split to produce O 2 (released from cell) and H + ions (released into lumen)
    • enzyme complexes pump protons from stroma to lumen
    • NADP + is final electron acceptor and produces NADPH
    • chemiosmosis to synthesize ATP
  • Analogy
  • Light Reaction Animation
    • http://www.youtube.com/watch?v=v590JJV96lc
    • http://www.youtube.com/watch?v=hj_WKgnL6MI&feature=related
  • Cyclic Electron Flow
  • Cyclic Electron Transfer Summary
    • only involves photosystem I (P700)
    • ferrodoxin returns electrons back to cytochrome complex
    • protons pumped into lumen to produce more ATP through chemiosmosis
    • no NADPH produced