Valgustusfosforüülatsioon

Valgustusfosforüülatsioon is a biological process that occurs in the thylakoid membranes of chloroplasts and cyanobacteria. It is the first stage of photosynthesis, where light energy is converted into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). This process is driven by the absorption of photons by chlorophyll and other pigments located within photosystems.

When light strikes the photosystems, it excites electrons. These high-energy electrons are then passed along a series of protein complexes embedded in the thylakoid membrane, known as the electron transport chain. As electrons move through the chain, energy is released, which is used to pump protons (H+) from the stroma into the thylakoid lumen. This creates a proton gradient across the thylakoid membrane.

The accumulated protons then flow back into the stroma through an enzyme called ATP synthase. This movement of protons provides the energy for ATP synthase to phosphorylate ADP (adenosine diphosphate) into ATP, a process that stores chemical energy. Simultaneously, electrons and protons are used to reduce NADP+ to NADPH, another energy-carrying molecule. Both ATP and NADPH produced during valgustusfosforüülatsioon are then used in the second stage of photosynthesis, the Calvin cycle, to fix carbon dioxide and synthesize sugars.