A protein is synthesised in the endoplasmic reticulum bound ribosomes and it targets to the inner thylakoid space of chloroplast. It has to pass three double-layered membrane layers to reach its destination. A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen.