Energetic and kinetic aspects of photosynthesis

The thylakoid membrane

The thylakoid membrane in green plants is the site of the light reactions of photosynthesis. These include the capture of light energy by light harvesting complexes, transfer of energy to the reaction center and charge separation across the member in the reaction center (RC). A similar process occurs in the inner member of photosynthetic bacteria. The electron transfer is converted into chemical energy by proton uptake and proton pumping. Ultimately the light reactions generate a transmembrane potential due to a pH difference across the thylakoid membrane.

PDF of photosynthesis lecture

Discussion of the physical chemistry of the photosynthetic reaction center.

Electron transfer reactions in photosynthesis and elsewhere

Marcus theory: the nuclear part of the rate constant

Electron transfer theory is a special case of first order kinetic theory that applies specifically to the transfer of an electron from a reactant (DA) to a product state (D+A-), where D and A are the donor and acceptor, respectively. The potential energy surfaces for the two states are assumed to be harmonic and the derivation of the activation energy is carried out using geometric arguments. Despite its simplicity, or perhaps because of its simplicity, Marcus theory has been widely used even in complex environments such as the photosynthetic RC. One preduction of March theory that is particularly relevent is the activationless electron transfer process, which occurs when ε = λ, where ε is the energy gap or energetic driving force for the electron transfer reaction and λ is the reorganization energy.

Derivation of the activation energy according to Marcus theory

The electronic couping: the electronic part of the rate constant

Relationship between the electronic coupling and the Marcus theory rate constant