Question

Transport vesicles play a major role in the movement of molecules throughout the cell. (15pts) (a) What role does clatherine and adaptin play in the secretory and endocytic pathway? (define all 4 terminologies) (b) Thoroughly explain how a molecule can enter the cell through receptor mediated endocytosis. Be sure to thoroughly explain each step and the role of each protein.

Answer 1

a) The role of clathrin and adaptin in the secretory and endocytic pathway:

• The secretory pathway is where the proteins and the lipids are synthesized in the endoplasmic reticulum and transported to golgi.
• The adaptins are the second class of protein coats that form a layer between the clathrin and the membrane.The adaptins secures the clathrin coat to the vesicle membrane.
• It selects a specific set of cargo molcules by trapping the cargo receptors that bind them.
• The clathrin has two main functions namely: It helps in the receptor mediated and fluid phase endocytosis from the plasma membrane to early endosome.
• It transports from the TGN and endosomes.
• The adaptins interact with the proteins in the plasma membrane that are targeted by endocytosis.
• Clathrin mediated endocytosis begins by the formation of pit in the plasma membrane.The pit is surrounded on the cytoplasmic side by the adaptor proteins that link clathrin to the pit.
• The endocytic pathway is subdivided into four categories namely the receptor mediated(clathrin mediated pathway),caveolae,macropinocytosis and phagocytosis.The pinocytosis is called the cell drinking and phagocytosis is the cell eating.

b) The entry of molecule into the cell through receptor mediated endocytosis:

In animal cells,the clathrin coated pits and vesicles provide an efficient pathway for taking up macromolecules from the extracellular fluid.This process is called receptor mediated endocytosis.The macromolecules bind to the complementary transmembrane receptor proteins,accumulate in coated pits and then enter the cell as receptors-macromolecule complexes in clathrin coated vesicles.Many animal cells take up cholestrol through receptor mediated endocytosis by this they acquire most of cholestrol to make up new membrane.