What mechanism does transferrin use to enter cells, as indicated by the presence of clathrin-coated vesicles?

Transferrin enters cells through the process of receptor-mediated endocytosis. This mechanism is characterized by the specific binding of transferrin to its receptor on the cell surface, which then triggers the invagination of the plasma membrane. This invagination is facilitated by clathrin, a protein that helps form a coated pit that subsequently pinches off to form a clathrin-coated vesicle containing the transferrin-receptor complex.

Receptor-mediated endocytosis is efficient and specific, allowing cells to internalize substances they need, such as iron bound to transferrin, which is crucial for processes like blood oxygen transport and cellular metabolism. The clathrin-coated vesicles are essential to this process, indicating that the uptake is mediated by specific receptors rather than being a nonspecific uptake of material.

The other mechanisms listed do not involve the specific targeting or the use of clathrin-coated vesicles in the same way. For example, phagocytosis typically involves the engulfing of larger particles or cells and is less specific, while pinocytosis is more associated with the uptake of liquids and small solutes, and exocytosis refers to the process of vesicles fusing with the plasma membrane to release their contents outside