Coat proteins are specialized proteins that play a crucial role in the formation of vesicles, which are small membrane-bound sacs within cells. These proteins help to shape the membrane and facilitate the transport of materials between different cellular compartments. They are essential for processes such as endocytosis and exocytosis, where substances are brought into or expelled from the cell. There are several types of coat proteins, including clathrin, COPI, and COPII. Each type has a specific function and is involved in different pathways of vesicle transport. For example, clathrin is primarily associated with the transport of molecules from the cell membrane, while COPII is involved in transporting proteins from the endoplasmic reticulum to the Golgi apparatus.