Light Dependent Stage Flashcards

1
Q

Where does it occur?

A

Thylakoids

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2
Q

What is a summary of what happens in the light dependent stage?

A
  • Photolysis occurs (H+, e- and oxygen produced)
  • High concentration of H+ in thylakoid lumen causes proton gradient
  • Electrons travel through electron transport chain in thylakoid membrane
  • NADP combine with H+ from stroma and e- in electron transport chain to form NADPH
  • ATP produced during photophosphorylation
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3
Q

What happens during photophosphorylation?

A
  • Excited electrons passed along ELTC
  • Electron carriers are alternately reduced and oxidised as electrons are passed from carrier to carrier
  • Excited electrons release energy as they are passed through ELTC
  • Energy released used to actively transport H+ across thylakoid membrane from stroma to thylakoid lumen via a proton pump
  • Proton gradient created, high conc of H+ in thylakoid lumen, low conc in stroma
  • H+ diffuses by facilitated diffusion across TRANSMEMBRANE ATP SYNTHASE enzymes back into the stroma
  • Releases energy for the synthesis of ATP from ADP + Pi
  • Can be cyclic or non-cyclic
  • Cyclic involves PSI, Non-Cyclic involves PSI and PSII
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4
Q

What are photosystems?

A
  • PSI and PSII
  • Collection of pigments that absorb light energy and transfer energy to electrons
  • Different pigment molecules are arranged in funnel like structures in thylakoid membrane
  • Each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre
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5
Q

What is PSI?

A
  • Contains primary pigment P700
  • Absorbs light of wavelength 700nm
  • In the middle of the electron transport chain
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6
Q

What is PSII?

A
  • Contains primary pigment P680
  • Absorbs light at a wavelength of 680nm
  • At beginning of ELTC
  • Where photolysis takes place
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7
Q

What is cyclic phosphorylation?

A
  • Light absorbed at PSI and passed to P700 (primary pigment of PSI)
  • Electron in primary pigment molecule becomes excited to a higher energy level
  • Photoactivation occurs
  • Excited electron released from chlorophyll molecule and accepted by an electron acceptor
  • Electron acceptor transports electrons to ELTC
  • As electrons pass through ELTC, they provide energy, chemiosmosis occurs, releasing energy for the synthesis of ATP
  • Electrons then transported BACK TO PSI
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8
Q

What is non-cyclic phosphorylation?

A
  • Light absorbed in PSII, passed to P680
  • 2 electrons in primary pigment molecule excited to higher energy level
  • Emitted from chlorophyll in process called photoionisation
  • Each excited electron passed down ELTC
  • Chemiosmosis occurs
  • THEN ELECTRONS PASSED TO PSI
  • PSII contains water-splitting enzyme called oxygen-evolving complex
  • Catalyses photolysis
  • H2O → 2H+ + 2e- + ½O2
  • Excited electrons leave PSII to go to PS1
  • They are replaced by electrons from photolysis of water
  • So as photoactivation of electrons in PSII, photoionisation of electrons in PSI occurs
  • Excited electrons from PSI pass along an ELTC
  • These electrons combine with H+ produced by photolysis of water, and carrier molecule NADP to form NADPH
  • 2H+ + 2e- + NADP → reduced NADP
  • NADPH passes to light-independent reaction to be used in synthesis of carbohydrates
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