Cytosis and the Fluid Mosaic Model
...hin the membrane. Two different types of proteins exist: integral proteins and peripheral proteins. Integral proteins go through the entire lipid bilayer, with each end of it exposed to the aqueous solution on the outside of the membrane. The hydrophobic region of the integral proteins consist of amino acids, which are generally folded in the alpha-helix formation. The other type of protein, the peripheral proteins, do not interact with the hydrophobic region of the bilayer at all. Instead, they are found on the surface of the membrane and in contact with the aqueous solution. Most of the time, the peripheral protein will be attached to the exposed end of the integral protein. The peripheral proteins which are internally located are held in place by the cytoskeleton of the cell, while the ones located externally are held in place by fibers from the extracellular matrix. The proteins located in the fluid mosaic model have many different functions. The six major functions that these proteins can carry out are transport, enzymatic activity, signal transduction, cell to cell recognition, intercellular joining, and attachment to the cytoskeleton and ECM. 2) Endocytosis and Exocytosis Exocytosis is the process by which the cell secretes macromolecules by the fusion of vesicles with the plasma membrane. In other words, when a transport vesicle is developed by the Golgi apparatus, the vesicle moves into the plasma membrane by means of the microtubules. Many secretory cells use exocytosis to secrete their products outside of the cell itself. An example of exocytosis is the simple columnar cells of the intestines. The goblet cells located within the columnar region secrete mucus for smooth passage of particles throughout the intestines. ` The events of endocytosis are the reverse of exocytosis, except for the fact that endocytosis uses different proteins. Endocytosis is the cellular uptake of macromolecules and particulate subs...