This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
What is the role of membrane protein clathrin? 
Select and explain. 
A. Cell motility, B. Cell shape, C. Exocytosis, D. Receptor-mediated endocytosis
D: Receptor-mediated endocytosis
Answer: D: Receptor-mediated endocytosis 
Explanation: The membraneprotein, clathrin is involved in receptor mediated endocytosis. It occurs at membrane indentations where the protein clathrin accumulates. Clathrin molecules have the shape of triskelions, with three legs radiating from a central hub. As endocytosis progresses, the clathrin molecules form a geometric array that surrounds the endocytotic vesicle. Once the complete vesicle is formed, the clathrin falls off and the three-legged proteins recycle to form another vesicle. Ref: Ganong's Review of Medical Physiology, 23rd Edition, Chapter 2