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Plasma Membrane - on one end and hydrophilic on the other...

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Plasma Membrane The plasma membrane is the structure that surrounds the cell. It controls the cell's interactions with other cells, i.e., sensitivity to the environment. This includes communication, identification, and protection. The cellular membrane also controls the passage of materials in and out of cell. This principle of selective permeability means that some things are allowed in (or out) while other substances are completely excluded (or kept in). Everything on the inside of the phospholipid bilayer is intracellular , while everything outside this barrier is extracellular . The plasma membrane is composed of several macromolecules, including a variety of lipids, proteins, and carbohydrates. Membrane Lipids Lipids constitute 90 to 99% of the plasma membrane, depending on the shape and function of the cell. The primary lipid is a phospholipid. Phospholipids are special lipids that are hydrophobic
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Unformatted text preview: on one end and hydrophilic on the other. Thus, the most energetically favorable arrangement is a double layer with the hydrophilic "heads" on the outside and the hydrophobic "tails" facing each other on the inside. Figure 1 The second major lipid in the cellular membrane is cholesterol . Cholesterol affects the fluidity of the membrane; the less cholesterol in the membrane the more rigid the membrane, while the higher the concentration of cholesterol the more fluid the membrane. Some cells require great flexibility (like red blood cells) while other cells require more rigid shapes. Glycolipids constitute about 5% of the lipids and are found only on the extracellular side. These special lipids contribute to the glycocalyx of the cell. The glycocalyx functions to allow cellular adhesion as well protection from harmful extracellular substances....
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