By Contributor | Updated Mar 24, 2022
Photosynthesis is the process by which green plants, algae, and some bacteria convert atmospheric carbon dioxide and water into sugars, using light energy. The reaction occurs in two distinct phases: the light‑dependent reactions and the Calvin cycle.
During the light‑dependent phase, photons are captured by chlorophyll and other pigments, exciting electrons that are shuttled through the photosynthetic electron transport chain. The resulting energy is stored in ATP and NADPH, which fuel the Calvin cycle.
Each photon carries more energy than a plant can utilize in a single step. Therefore, absorbed light excites a pair of electrons in chlorophyll, which are then passed sequentially through a series of carriers, gradually dissipating energy as a proton gradient and producing ATP and NADPH.
Plastoquinone is the second carrier in the chain. It receives electrons from pheophytin and delivers them to the cytochrome b₆f complex, while concurrently shuttling protons into the thylakoid lumen to contribute to the proton motive force.
Plastocyanin is a copper‑containing soluble protein that accepts electrons from the cytochrome b₆f complex and transfers them to Photosystem I. Because plastocyanin requires copper, this metal is essential for optimal photosynthetic performance.
Ferredoxin is a small iron‑sulfur protein that operates outside the main electron transport chain. It receives electrons from Photosystem I and delivers them to NADP⁺ reductase, facilitating the reduction of NADP⁺ to NADPH.
