Fotofoszforiláció

Fotofoszforiláció is a biological process that occurs in photosynthetic organisms, such as plants, algae, and cyanobacteria. It is the mechanism by which light energy is converted into chemical energy in the form of adenosine triphosphate (ATP). This process is a crucial part of photosynthesis, the overall process that converts light energy into chemical energy that organisms can use for cellular activities.

The process begins with the absorption of light energy by pigment molecules, primarily chlorophyll, located within specialized organelles called chloroplasts. This absorbed light energy excites electrons within the chlorophyll molecules, raising them to a higher energy level. These high-energy electrons are then passed along a series of protein complexes embedded within the thylakoid membranes of the chloroplast.

As the electrons move through this electron transport chain, their energy is gradually released. This energy is used to pump protons (hydrogen ions) from the stroma of the chloroplast into the thylakoid lumen, creating a proton gradient across the thylakoid membrane. This gradient represents a form of stored potential energy.

The protons then flow back across the thylakoid membrane into the stroma through a protein complex called ATP synthase. This flow of protons drives the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi). This ATP molecule represents the chemical energy captured from light.

There are two main types of photophosphorylation: cyclic and non-cyclic. Non-cyclic photophosphorylation involves both photosystems I and II and results in the production of ATP and NADPH, another energy-carrying molecule. Cyclic photophosphorylation involves only photosystem I and primarily produces ATP. The ATP produced during photophosphorylation is then used to power the light-independent reactions of photosynthesis (the Calvin cycle), where carbon dioxide is converted into sugars.