bio Study Guide 2 - Study Guide#2 The two layers of...

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Study Guide #2 The two layers of phospholipids are arranged in a way that their hydrophobic tails are projecting to the interior whereas their hydrophilic heads are projecting the exterior. This organization of phospholipids in the cell membranes makes the latter selectively permeable to ions and molecules. Non-polar ions such as sodium, potassium and calcium require membrane proteins for transport. The process requires energy. Molecules that are non-polar can pass through the phospholipid bilayer without assistance. This includes oxygen and carbon dioxide. The plasma membrane is composed of different kinds of macromolecules. The components of a plasma membrane are integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, lipoproteins. Passive transport does not involve chemical energy, because, unlike in an active transport, the transport across membrane is always coupled with the growth of entropy of the system. So passive transport is dependent on the permeability of the cell membrane, which, in turn, is dependent on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis. o Diffusion is the net movement of material from an area of high concentration to an area with lower concentration. The difference of concentration between the two areas is often termed as the concentration gradient, and diffusion will continue until this gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient" o Facilitated diffusion, also called carrier-mediated diffusion, is the movement of molecules across the cell membrane via special transport proteins that are embedded within the cellular membrane. Many large molecules, such as glucose, are insoluble in lipids and too large to fit through the membrane pores. Therefore, it will bind with its specific carrier proteins, and the complex will then be bonded to a receptor site and
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moved through the cellular membrane. Bear in mind, however, that facilitated
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This note was uploaded on 02/21/2012 for the course BIO 311 C taught by Professor Mcclelland during the Fall '09 term at University of Texas.

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bio Study Guide 2 - Study Guide#2 The two layers of...

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