Question

Describe the cellular mechanism of formation of transport vesicles.

Answer 1

Vesicular transport involves the formation of a vesicle by budding from the cell membrane. The cytoplasmic surfaces of these vesicles are coated with proteins, and assembly of the coat proteins lead to vesicle budding by distorting the conformation of the membrane. There are three types of protein coated vesicles that aid in cellular transport. First is clathrin-coated vesicles, responsible for the uptake of extracellular molecules from the plasma membrane by the process of endocytosis as well as the movement of molecules from the trans Golgi network to lysosomes. Other types of vesicle involve nonclathrin-coated or COP-coated vesicles. COP-II coated vesicles bud from ER and use the secretory pathway to carry the cargo proteins to the Golgi apparatus. COPI-coated vesicles bud from the ER-Golgi compartment or the Golgi apparatus and help to retain resident proteins in the Golgi and ER. Each of these proteins have a secretory signal. Many adapter molecules like Arf, Rabs are extensively involved in trafficking along with formation of transport vesicles. Dynamin help in the scission of clathrin-coated vesicles from the plasma membrane during endocytosis. Emergence of tubules due to certain forces along with vesicular fusion further aid in the process of vesicular transport. Further SNARE proteins also play a fundamental role in vesicular fusion (v and t SNAREs).