mechanims of membrane transport

Q: How do cells use an elaborate internal membrane system to add and remove cell-surface proteins?

A: Cells use an elaborate internal membrane system to add and remove cell-surface proteins, such as receptors, ion channels, and transporters, through the process of exocytosis and endocytosis. Exocytosis involves the delivery of newly synthesized proteins, carbohydrates, and lipids to the plasma membrane or extracellular space, while endocytosis involves the internalization of plasma membrane components and the uptake of small particles and nutrients.

Q: What is the interior space of each membrane-enclosed compartment along the secretory and endocytic pathways equivalent to?

A: The interior space, or lumen, of each membrane-enclosed compartment along the secretory and endocytic pathways is equivalent to the lumen of most other membrane-enclosed compartments and to the cell exterior, in the sense that proteins can travel in this space without having to cross a membrane as they are passed from one compartment to another.

Q: What do transport vesicles carry and how do they move?

A: Transport vesicles carry membrane components and soluble lumenal molecules from one compartment to another. They continually bud off from one membrane and fuse with another, carrying their cargo along organized, directional routes.

Q: What is the route of the secretory pathway and where does it lead?

A: The secretory pathway leads outward from the endoplasmic reticulum (ER) toward the Golgi apparatus and cell surface, with a side route leading to lysosomes.

Q: What is the route of the endocytic pathway and where does it lead?

A: The endocytic pathway leads inward from the plasma membrane to internal compartments.

Q: What is the function of retrieval pathways in vesicular transport?

A: Retrieval pathways balance the flow of membrane between compartments in the opposite direction, bringing membrane and selected proteins back to the compartment of origin.