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The energy of P680 + is used in two steps to split a water molecule into 2H + + 1/2 O 2 + 2e-(photolysis or light-splitting). An electron from the water molecule reduces P680 + back to P680, while the H + and oxygen are released.
The antenna complex contains hundreds of chlorophyll molecules which funnel the excitation energy to the center of the photosystem. At the reaction center, the energy will be trapped and transferred to produce a high energy molecule. [2] The main function of PSII is to efficiently split water into oxygen molecules and protons.
The electron transport chain of photosynthesis is often put in a diagram called the Z-scheme, because the redox diagram from P680 to P700 resembles the letter Z. [3] The final product of PSII is plastoquinol, a mobile electron carrier in the membrane.
Photosystem I [1] is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin. Ultimately, the electrons that are transferred by Photosystem I are used to produce the moderate-energy hydrogen carrier NADPH. [2]
Plastoquinone (PQ) is a terpenoid-quinone (meroterpenoid) molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis.The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4-benzoquinone molecule with a side chain of nine isoprenyl units.
Photosynthesis occurs in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the hydrogen carrier NADPH and the energy-storage molecule ATP. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide.
When the photon has been absorbed, the resulting high-energy electron is transferred to a nearby pheophytin molecule. This is above and to the right of the pair on the diagram and is coloured grey. The electron travels from the pheophytin molecule through two plastoquinone molecules, the first tightly bound, the second loosely bound.
The following is a breakdown of the energetics of the photosynthesis process from Photosynthesis by Hall and Rao: [6]. Starting with the solar spectrum falling on a leaf, 47% lost due to photons outside the 400–700 nm active range (chlorophyll uses photons between 400 and 700 nm, extracting the energy of one 700 nm photon from each one)