Final answer:
The movement of membrane proteins after a mouse cell is fused with a human cell is initially unrestricted within the fused cell membranes, allowing free lateral movement. This movement can be constrained by the cell's cytoskeletal elements, according to the 'Fences and Pickets' model. Protein trafficking and functional interactions within the cell membrane depend on this lateral mobility.
Step-by-step explanation:
When a mouse cell is fused with a human cell, the movement of the respective membrane proteins is initially unrestricted, and they can freely move and intermix between the mouse and human cell membranes. This phenomenon was demonstrated through an experiment where mouse and human cells were fused to create hybrid cells, and antibodies tagged with fluorescent markers for the respective membrane proteins showed lateral movement in the fused cell membranes under a fluorescence microscope. The proteins are not static; they can move laterally and mix within the 'sea of phospholipids' that make up the cell membranes.
However, this fluid movement can be restricted by the cell's cytoskeletal elements. This happens through a phenomenon known as the 'Fences and Pickets' model, where integral membrane proteins are immobilized if they are attached to cytoskeletal fibers like actin in the cytoplasm, forming compartments that inhibit free movement across them. Therefore, unless membrane proteins are bound to the cytoskeleton, they generally move freely within the membrane, a property that is essential for protein trafficking and various cellular functions.