Transport Protein

Transport Proteins of eukaryotic cells function as either carriers or channels.

Carriers are analogous to proteins in prokaryotic cells that mediate facilitated diffusion and active transport.  See figure 1.2 and 1.3 for facilitated diffusion and active transport.

Figure 1.2 Facilitated Diffusion


Figure 1.3 Active Transport

Channels are pores in the membrane.  These pores are so small that only specific ions can diffuse through.  Cells of multicellular organisms often take up nutrients by facilitated diffusion (figure 1.3), because the nutrient concentration of surrounding environments can be controlled.

See the videos below for an animated description of facilitated diffusion and active transport 


Endocytosis (figure 1.4) is the process by which eukaryotic cells take up materials from the surrounding environment.  The type of endocytosis most common to animal is pinocytosis. In this process, a cell internalizes and pinches off small pieces of its own membrane, bringing along a small volume of liquid and any  materials attached to the membrane.   Protozoa and phagocytes use a specific type of endocytosis called phagocytosis. The cell sends out armlike extension which surround and enclose extracellular material.  This envelopes the materials, bringing it into the cell in an enclosed compartment.  



Figure 1.4 Endocytosis

The process of exocytosis (Figure 1.5) is the reverse of endocytosis.  Membrane-bound vesicles inside the cell fuse with the plasma membrane and release its content into the external medium.  


Figure 1.5  Exocytosis


 See the videos below for an animated description of Endocytosis and Exocytosis 



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