The Structure of Biological Membrane Essay Example | Topics and Well Written Essays - 2000 words

The Structure of Biological Membrane - Essay ExampleHowever, membranes are not only passive barriers. They include a set of proteins specialized for promoting or catalyzing various stallular processes (Nelson & Cox 2004, p.369). Molecular transportation is the most important function of membranes facilitated by carrier and channel proteins (McKee 2004, p.62). full general questions of transportation and channeling across biologic membranes are well considered in the encompassing textbooks of Lodish (2003, p.245-300), Nelson & Cox (2004, p.369-420), Kuchel & Ralston (1997, p.171-184), McKee (2004, p.353-366), Garrett & Grisham (1999, p.259-326), etc., in special monographs, e.g. Keizer (2000) and also in a variety of articles. any cells acquire from its environs the raw materials for biosynthesis and for energy production, and also release to its environment the byproducts of metabolism. Only some non polar compounds can cross the membrane unassisted. However, for polar or charged c ompounds or ions, a membrane protein is essential for transmembrane movement.Membrane transport mechanisms are vital to living organisms. Ions and molecules constantly move across cell plasma membranes and across the membranes of organelles. This flux must be regulated to meet each cells metabolic needs. For example, a cells plasma membrane regulates the entrance of nutrient molecules and the overtaking of waste products. Additionally, it regulates intracellular ion concentrations. Because lipid bilayers of membranes are generally impenetrable to ions and polar substances, specific transport components must be inserted into cellular membranes (McKee 2004, p.372). In the simplest cases a membrane protein facilitates the diffusion of a solute down its concentration gradient. However, transportation often occurs against a gradient of concentration, electrical charge, or both. In such cases, solutes must be handle that requires energy. The necessary energy may come from ATP hydrolysi s (i.e. directly), or may be supplied indirectly, e.g. in the form of movement of another solute down its electrochemical gradient with enough energy to carry another solute up its gradient (Nelson & Cox 2004, p.389 Garrett & Grisham 1999, p.296). Ions may also move across membranes via ion channels formed by proteins, or they may be carried across by ionophores, sensitive molecules that mask the charge of the ions and allow them to diffuse through and through the lipid bilayer of membrane. With very few exceptions, the traffic of small molecules across the plasma membrane is mediated by proteins such as transmembrane channels, carriers, or pumps (Nelson & Cox 2004, p.391). So, ions cannot pass freely through the cells phospholipid membrane. Instead, most ions flow through special channels built from multiple protein subunits. These subunits together form a pore across the membrane. Some channels are gated, fitted with proteins that act as hinged doors, city block the opening unti l