How a Photosystem Harvests Light A primary electron acceptor in the reaction

How a photosystem harvests light a primary electron

This preview shows page 27 - 34 out of 53 pages.

How a Photosystem Harvests Light A primary electron acceptor in the reaction center STROMA Photon Photosystem Accepts an excited electron from chlorophyll a Primary electron acceptor Reaction-center complex Light-harvesting complexes Redox reaction e membrane Solar-powered transfer of an electron from a hl h ll l l Thylakoid m chlorophyll a molecule to the primary electron acceptor THYLAKOID SPACE (INTERIOR OF THYLAKOID) Pigment molecules Transfer of energy Special pair of chlorophyll a molecules The first step of the light reactions
Image of page 27
Linear Electron Flow During the light reactions, there are two possible routes for electron flow Cyclic Linear Primary acceptor 4 P Primary acceptor Linear electron flow The primary pathway P680 e 2 e e 2 H + O 2 + 3 H 2 O 1 / 2 Pq Pc Cytochrome complex 5 Light e P700 Involves both photosystems Two photosystems in the thylakoid membrane PSII Pigment molecules Light 1 ATP Ph t t 6 PSI Produces ATP and NADPH using light energy Photosystem I Photosystem I (PS I) II (PS II)
Image of page 28
How a Photosystem Harvests Light Two types of photosystems in the thylakoid membrane Photosystem II (PS II) Functions first Primary acceptor 4 P Primary acceptor The numbers reflect order of discovery Is best at absorbing a wavelength of 680 nm P680 e 2 e e 2 H + O 2 + 3 H 2 O 1 / 2 Pq Pc Cytochrome complex 5 Light e P700 The reaction-center chlorophyll a of PS II Called P680 Pigment molecules Light 1 ATP Ph t t 6 Photosystem I (PS I) Best at absorbing a wavelength of 700 nm Photosystem I Photosystem I (PS I) II (PS II) The reaction-center chlorophyll a of PS I is called P700
Image of page 29
How Linear Electron Flow During the Light Reactions Generates ATP and NADPH Light reactions use solar e e e ATP power Generate ATP and NADPH NADPH e e e Provide chemical energy and reducing power Mill makes ATP Carbohydrate- synthesizing reactions of the Calvin cycle Photosystem II Photosystem I e Energy of electrons as they flow through the light reaction Shown in a mechanical analogy
Image of page 30
How Linear Electron Flow During the Light Reactions Generates ATP and NADPH A photon hits a pigment Its energy is passed among pigment e 2 Primary acceptor molecules until it excites P680 P680 An excited electron f P680 Light 1 from P680 Transferred to the primary electron Pigment molecules Photosystem II acceptor (PS II)
Image of page 31
How Linear Electron Flow During the Light Reactions Generates ATP and NADPH P680 + is a very strong oxidizing agent P6 0 h e Primary acceptor 2 2 H + H 2 O P680 that is missing an electron P680 e e O 2 + 3 1 / 2 H 2 O is split by enzymes The electrons are transferred from the Light 1 hydrogen atoms to P680 + Thus reducing it to Pigment molecules Photosystem P680 O 2 is released as a by- II is released as a by product of this reaction (PS II)
Image of page 32
How Linear Electron Flow During the Light Reactions Generates ATP and NADPH Each electron “falls” down an electron transport chain From the primary Primary 4
Image of page 33
Image of page 34

You've reached the end of your free preview.

Want to read all 53 pages?

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture