Fatty acids nonpolar tail/head

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

Figure 5.2 A phospholipid molecule is shown in the image above with a head, which has phosphate and oxygen atoms, and a tail made of two fatty acid chains. The head has atoms that are polar, or charged, and therefore they "like" water. This includes phosphate (purple), oxygen (red), and nitrogen (blue). The tail has chains of carbon atoms (green) that are nonpolar, and therefore they "dislike" water.

Figure 4-1. Structures of the membrane bilayer and an amphipathic phospholipid. The head group attachment, X, may be H as in phosphatidic acid or one of several substituents linked via phosphoesters in the glycerophospholipids. The nonpolar tail is depicted as composed of saturated fatty acids in this molecule. The overall length of the hydrocarbon chain of the fatty acids may vary from 14 to 20.

The polar lipids, with polar heads and nonpolar tails, are major components of membranes. The most abundant are the glycerophospholipids, which contain fatty acids esterified to two of the hydroxyl groups of glycerol, and a second alcohol, the head group, esterified to the third hydroxyl of glycerol via a phosphodiester bond. Other polar lipids are the sterols. 

The long fatty acid tail is nonpolar and does not attract water molecules. The polar and nonpolar parts of phospholipids allow them to form lipid bilayers. Bi is from Latin and means two. The bilayer forms when the phospholipid molecules arrange themselves in two layers with the tails facing in (facing each other) and the heads facing out. The result is a phospholipid bilayer that has the tails buried inside and the polar atoms of the heads facing out, where they can form H bonds with water and other molecules. 

The cleaning action of soap is due to the dual nature of the conjugate base of the fatty acid molecule. On one end is the ionic carboxylate anion group the rest of the molecule consists of a nonpolar hydrocarbon chain. The tonic part, called the head is attracted to a polar solvent such as water and is hydrophilic, whereas the long hydrocarbon tail is hydrophobic. In water, soap molecules tend to group together in clusters called micelles, with their ionic heads oriented toward the water molecules and their hydrocarbon tails in the interior of the cluster so that unfavorable interactions with water are avoided. Non-... 

The phosphorus side chain of a phosphoacylglycerol makes it different from a triacylglycerol. The two fatty acid side chains form two nonpolar tails that lie parallel to each other, while the phosphodiester end of the molecule is a charged or polar head. A three-dimensional stmcture of a phosphoacylglycerol is shown in Figure 29.3. 

As discussed in Section 3.7, when these phospholipids are mixed with water, they assemble in an arrangement called a lipid bilayer. The ionic heads of the phospholipid are oriented on the outside and the nonpolar tails on the inside. The identity of the fatty acids in the phospholipid determines the rigidity of this bilayer. When the fatty acids are saturated, they pack well in the interior of the lipid bilayer. and the membrane is quite rigid. When there are many unsaturated fatty acids, the nonpolar tails cannot pack as well and the bilayer is more fluid. Thus, important characteristics of this lipid bilayer are determined by the three-dimensional stmcture of the molecules that comprise it. 

A phosphoacylglycerol has two distinct regions two nonpolar tails due to the long-chain fatty acids, and a very polar head from the charged phosphodiester. 

Solid soaps are usually sodium salts of long-chain organic acids called fatty acids. They have a polar head and a nonpolar hydrocarbon tail. Sodium stearate, a typical soap, is shown here. 

The chemical structure of soap explains its cleaning ability. There are two main parts of a soap s structure. Soap molecules contain a nonpolar alkyl tail and a polar head that can interact with the polar water molecules. A soap solution is not a true solution, it doesn t have individual fatty acid anions in the water, but rather groups of these ions called micelles. 

Phospholipids are a group of lipids that are phosphate esters. The presence of the phosphoryl group results in a molecule with a polar head (the phosphoryl group) and a nonpolar tail (the alkyl chain of the fatty acid). Because the phosphoryl group ionizes in solution, a charged lipid results. 

The fluid mosaic model of membrane structure pictures biological membranes that are composed of lipid bilayers in which proteins are embedded. Membrane lipids contain polar head groups and nonpolar hydrocarbon tails. The hydrocarbon tails of phospholipids are derived from saturated and unsaturated long-chain fatty acids containing an even number of carbon atoms. The lipids and proteins diffuse rapidly in the lipid bilayer but seldom cross from one side to the other. 

Phospholipids are an important class of biomolecules. Phosphohpids are the fundamental building blocks of cellular membranes and are the major part of surfactant, the film that occupies the air/liquid interfaces in the lung. These molecules consist of a polar or charged head group and a pair of nonpolar fatty acid tails, connected via a glycerol linkage. This combination of polar and nonpolar segments is termed amphiphific, and the word describes the tendency of these molecules to assemble at interfaces between polar and nonpolar phases. 

In aqueous solution, soap forms micelles, with the polar heads (carboxylate groups) on the surface and the nonpolar tails (fatty acid R groups) in the interior. 

An ester of glycerol containing two fatty acids consists of a long nonpolar "tail" and a polar substituted-phosphate "head"... 

Phospholipids are similar in stmcture to fats in that they are esters of glycerol. Unlike fats, however, they contain only two fatty acids. The third group bound to glycerol is a phosphate group, which gives phospholipids two distinct parts the long nonpolar "tail" and the polar substituted-phosphate "head" (see Figure 21.21). 

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