Tilakoidokon

Tilakoidokon is a term used to describe the thylakoid membranes and their lumen in photosynthetic organisms. These membrane-bound sacs are located within chloroplasts of green plants and algae, and in cyanobacteria their function is analogous. In most plants, tilakoidokon are arranged into stacks called grana, connected by stroma lamellae. The interior space of a thylakoid sac is called the thylakoid lumen, while the surrounding fluid is the stroma.

Biochemistry and composition: The tilakoidokon membrane contains photosystems I and II, the cytochrome b6f complex, ATP synthase, and various electron carriers such as plastoquinone and plastocyanin. Pigments including chlorophyll a, chlorophyll b, and carotenoids are embedded in the membrane. The lumen hosts a protoned environment created by electron transport, which is essential for ATP production.

Function: The primary role is to carry out light-dependent reactions of photosynthesis. Light energy excites chlorophyll in photosystems, driving electron transport from water (split by PSII to release O2) through the chain to NADP+, forming NADPH. The electron transport also pumps protons into the thylakoid lumen, creating a gradient that drives ATP synthase to produce ATP in the stroma. This ATP, together with NADPH, powers the Calvin cycle for carbon fixation.

Distribution and variation: While the basic layout is conserved, grana size and number vary with species, light conditions, and developmental stage. In cyanobacteria, tilakoid membranes serve a similar purpose but are organized differently within the cytoplasm.