An Introduction to Chemiosmosis

1
An Introduction to Chemiosmosis
2
Electron Transport Overview

• Electrons pass through a non-cyclic electron
  transport chain and provide energy to pump H
  ions from the stroma, across the thylakoid
  membrane to the thylakoid compartment.

3
Chemiosmosis

• Chemiosmosis Source of ATP production in
  photophosphorylation.

4

• Takes place in Chloroplasts in the thylakoid.

5
Photosystem II

• The energy from the photon is captured by a
  pigment molecule from the photosystem.
• This energy is passed to other pigments until it
  reaches the chlorophyll molecule.
• Light energy is used to oxidize water and this
  produces electrons, protons (H) and oxygen gas.
• The chlorophyll molecule is oxidized and carries
  a positive charge. Therefore the electron
  acceptor is reduced.

6
Redox Reactions in Thylakoid Membrane

• Excited electrons reduce plastoquinone, an
  electron acceptor.
• The energy moves H ions across the membrane into
  the thylakoid interior.
• Plastoquinone is oxidized and electrons move to
  cytochrome, which is reduced.
• Cytochrome passes the electrons to plastocyanin
  making cytochrome oxidized and plastocyanin
  reduced.

7
Redox Reactions
8
Photosystem I

• Absorbs light energy, and each photon donates an
  electron to electron acceptor, which in this case
  is ferredoxin

9
NADP Reductase

• Reduced ferredoxin donates two electrons to NADP
  reductase
• Also takes two H from stroma thereby reducing
  NADP to NADPHH

10
ATP Synthesis

• Due to the pH difference, H ions diffuse back to
  the stroma through ATP synthase channels and form
  ATP from ADP P
• The production of ATP through the use of proton
  gradient is called photophosphorylation or
  chemiosmosis

11
Overview of Chemiosmosis

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