tilakoide

A thylakoid is a membrane-bound compartment found within chloroplasts and cyanobacteria. These flattened sacs or vesicles are the sites of the light-dependent reactions of photosynthesis. Thylakoids are typically arranged in stacks called grana, though they can also exist as single, unstacked lamellae, often connecting grana. The thylakoid membrane itself is a lipid bilayer containing chlorophyll and other pigments, as well as electron transport chains and ATP synthase complexes. These components are crucial for capturing light energy and converting it into chemical energy in the form of ATP and NADPH. The internal space of the thylakoid is called the lumen, which plays a role in establishing a proton gradient essential for ATP synthesis. The thylakoid system is a fundamental structure for energy conversion in photosynthetic organisms, enabling them to produce sugars from carbon dioxide and light.