Final answer:
Dynamin is required for the severing of clathrin-coated vesicles during receptor-mediated endocytosis, where it functions to cleave the vesicle from the plasma membrane, enabling the internalization and processing of substances within the cell.
Step-by-step explanation:
Severing of newly formed clathrin-coated vesicles from the plasma membrane requires dynamin to cleave. This process is essential in receptor-mediated endocytosis, where extracellular substances bind to cell membrane receptors and are internalized through vesicles.
Dynamin, a GTPase enzyme, is pivotal in the "pinch-off" stage of vesicle formation, wherein it wraps around the neck of the budding vesicle and, through GTP hydrolysis, constricts and severs the vesicle from the plasma membrane. Once internalized, the vesicles shed their clathrin coat, and the uncoated vesicle fuses with an early endosome for sorting.
This compartmentalization allows for the separation of the internalized substances from their receptors, which can be recycled back to the membrane, while the vesicle continues to a lysosome for content degradation and utilization by the cell.