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The hydrophilic end usually contains a negatively charged phosphate group, and the hydrophobic end usually consists of two "tails" that are long fatty acid residues. [ 4 ] In aqueous solutions, phospholipids are driven by hydrophobic interactions , which result in the fatty acid tails aggregating to minimize interactions with the water molecules.
The heads of glycolipids (glyco- stands for sugar) contain a sphingosine with one or several sugar units attached to it. The hydrophobic chains belong either to: two fatty acids (FA) – in the case of the phosphoglycerides, or; one FA and the hydrocarbon tail of sphingosine – in the case of sphingomyelin and the glycolipids.
In some cases, both hydrophilic and hydrophobic properties occur in a single molecule. An example of these amphiphilic molecules is the lipids that comprise the cell membrane . Another example is soap , which has a hydrophilic head and a hydrophobic tail, allowing it to dissolve in both water and oil.
The biological membrane is made up of lipids with hydrophobic tails and hydrophilic heads. [6] The hydrophobic tails are hydrocarbon tails whose length and saturation is important in characterizing the cell. [7] Lipid rafts occur when lipid species and proteins aggregate in domains in the membrane.
The origin of this energy is the fact that creating such an interface exposes some of the lipid tails to water, but the exact orientation of these border lipids is unknown. There is some evidence that both hydrophobic (tails straight) and hydrophilic (heads curved around) pores can coexist. [85] [86]
The arrangement of hydrophilic heads and hydrophobic tails of the lipid bilayer prevent polar solutes (ex. amino acids, nucleic acids, carbohydrates, proteins, and ions) from diffusing across the membrane, but generally allows for the passive diffusion of hydrophobic molecules.
Most surfactants are organic compounds with hydrophilic "heads" and hydrophobic "tails." The "heads" of surfactants are polar and may or may not carry an electrical charge. The "tails" of most surfactants are fairly similar, consisting of a hydrocarbon chain, which can be branched, linear, or aromatic. Fluorosurfactants have fluorocarbon chains.
They are usually organized into a bilayer in membranes with the polar hydrophilic heads sticking outwards to the aqueous environment and the non-polar hydrophobic tails pointing inwards. [6] Glycerophospholipids consist of various diverse species which usually differ slightly in structure. The most basic structure is a phosphatidate.