How does photosynthetic electron transfer work?
Photon capture causes changes in redox potential. Electrons then flow in order to generate ΔP.
• Capture causes a change in redox potential from electropositive to electronegative.
• Electrons flow through a cyclic or non-cyclic pathway to generate ΔP.
• ETCs are very similar compared to respiratory chains.
• Photosynthesis uses antennae complexes.
• Reaction centres contain pigment. The pigment is excited by a photon. This turns the pigment into a powerful reducing agent like quinone.
• The pigment becomes a very short-lived cation.
• The cation becomes an oxidising agent which accepts electrons from donor molecules and returns to a pigment molecule in its ground state.
How do the antennae complexes work?
Antennae complexes are used to increase the range of wavelengths which can be absorbed by organism.
• The individual reaction centre is hit by a proton once every second.
• However, turnover is more than 100 per second. A collection process is required.
• This is achieved by pigment molecules attached to polypeptide chains.
• The pigments have their electrons excited to higher energy levels.
• The energy can be transferred by FRET, which does not use any radiation. It is dependent on distance and orientation.
• The other method is a direct interaction between molecular orbitals called delocalised exciton coupling, which involves electron exchange. It occurs over distances of less than 1.5 nm.
• Using transfer complexes is more effective than having multiple reaction centres.
• Overall around 90% of photons which are absorbed are delivered to the reaction centre.
