Directions: Fully answer each question on the lines provided. Write in complete sentences. 1. Diagram the processes of nOTH endocytosis \( \Delta N D \) exocytosis in the space below. Explanations must bewritten. ( 6 Points) Endocytosis

### Endocytosis 1. **Membrane Invagination:** The plasma membrane begins to fold inward to engulf extracellular material. This process starts when receptors on the cell surface bind to specific ligands, initiating the formation of a vesicle. \[ \text{Plasma Membrane} \rightarrow \text{Invagination} \] 2. **Vesicle Formation:** As the membrane continues to invaginate, a small pocket or vesicle is formed, enclosing the extracellular content. Once the vesicle is fully formed, it pinches off from the plasma membrane using proteins like clathrin. \[ \text{Invagination} \longrightarrow \text{Vesicle} \quad (\text{using proteins like clathrin}) \] 3. **Internalization and Transport:** The vesicle is now free in the cytoplasm, where it can fuse with early endosomes for further sorting and processing of its content. \[ \text{Vesicle} \rightarrow \text{Early Endosome} \] ### Exocytosis 1. **Vesicle Transport:** In exocytosis, vesicles containing substances destined for secretion are transported from the Golgi apparatus to the plasma membrane. \[ \text{Golgi Apparatus} \rightarrow \text{Transport Vesicle} \] 2. **Docking and Fusion:** The vesicle docks at the plasma membrane and, through a process mediated by SNARE proteins, the vesicle membrane fuses with the cell membrane. \[ \text{Docking} + \text{SNARE proteins} \rightarrow \text{Membrane Fusion} \] 3. **Release of Contents:** Once fusion is completed, the vesicle releases its contents into the extracellular space. This process is crucial for neurotransmitter release, hormone secretion, and other cell signaling mechanisms. \[ \text{Vesicle} \rightarrow \text{Extracellular Release} \] Each step in these processes involves a series of coordinated molecular events that ensure the correct internalization or secretion of substances, maintaining cellular function and communication.