Search for:. Learning Objective Describe phospholipids and their role in cells. Key Points Phospholipids consist of a glycerol molecule, two fatty acids, and a phosphate group that is modified by an alcohol.
The phosphate group is the negatively-charged polar head, which is hydrophilic. The fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic.
Since the tails are hydrophobic, they face the inside, away from the water and meet in the inner region of the membrane. Since the heads are hydrophilic, they face outward and are attracted to the intracellular and extracellular fluid. If phospholipids are placed in water, they form into micelles, which are lipid molecules that arrange themselves in a spherical form in aqueous solutions. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet.
October 22, October 16, Licenses and Attributions. A molecular theory of lipid—protein interactions in the plasma lipoproteins.
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Mechanism and determinants of amphipathic helix-containing protein targeting to lipid droplets. Fagarasanu A. Maintaining peroxisome populations: A story of division and inheritance. Cell Dev. Smith J. Peroxisomes take shape. Cell Biol.
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A familiar is example is the way liquid dishwashing detergent isolates oils from greasy dishes. In aqueous solutions, amphipathic molecules spontaneously assemble into micelles. A micelle has lower free energy than free-floating amphipaths. The polar portion of the amphipath the hydrophilic part forms the outer surface of the micelle and is exposed to water.
The lipophilic portion of the molecule which is hydrophobic is shielded from the water. Any oils in the mixture are isolated within the interior of the micelle. Hydrogen bonds stabilize the hydrocarbon chains within the micelle. Energy is required to break a micelle apart.
Amphipaths can also form liposomes. Liposomes consist of an enclosed lipid bilayer that forms a sphere. The outer, polar portion of the bilayer faces and encloses an aqueous solution, while the hydrophobic tails face each other. Detergents and soaps are familiar examples of amphipathic molecules, but many biochemical molecules are also amphipaths. Examples include phospholipids, which form the basis of cell membranes. Cholesterol, glycolipids, and fatty acids are amphipaths which also incorporate into cell membranes.
Bile acids are steroid amphipaths used to digest dietary fats. There are also categories of amphipaths. Amphipols are amphiphilic polymers that maintain membrane protein solubility in water without the need for detergents. The use of amphipols allows the study of these proteins without denaturing them. Bolaamphipathic molecules are those that have hydrophilic groups at both ends of a ellipsoid-shaped molecule.
Compared to amphipaths with a single polar "head," bolaamphipaths are more soluble in water. Fats and oils are a class of amphipaths. They dissolve in organic solvents, but not in water.
Hydrocarbon surfactants used for cleaning are amphipaths. Examples include sodium dodecyl sulfate, 1-octanol, cocamidopropyl betaine, and benzalkonium chloride. Amphipathic molecules serve several important biological roles.
They are the primary component of the lipid bilayers that form membranes. Sometimes there is a need to alter or disrupt a membrane. Here, the cell uses amphipathic compounds called pepducins that push their hydrophobic region into membrane and expose the hydrophilic hydrocarbon tails to the aqueous environment.
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