Key PointsPhospholipids covers a glycerol molecule, 2 fatty acids, and a phosphate team that is modified by an alcohol.The phosphate team is the negatively-charged polar head, i beg your pardon is hydrophilic.The fatty mountain chains room the uncharged, nonpolar tails, which room hydrophobic.Since the tails are hydrophobic, they face the inside, far from the water and also meet in the inner region of the membrane.Since the heads are hydrophilic, they face outward and also are attractive to the intracellular and also extracellular fluid.If phospholipids are placed in water, they type into micelles, which space lipid molecules the arrange us in a spherical form in aqueous solutions.

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TermsmicelleLipid molecules the arrange themselves in a spherical type in aqueous solutions.amphipathicDescribing a molecule, such as a detergent, which has both hydrophobic and also hydrophilic groups.

Defining characteristics of Phospholipids

Phospholipids are significant components of the plasma membrane, the outermost layer of animal cells. Prefer fats, they space composed the fatty acid chains attached come a glycerol backbone. Uneven triglycerides, which have three fat acids, phospholipids have two fat acids the help kind a diacylglycerol. The 3rd carbon that the glycerol backbone is likewise occupied by a modification phosphate group However, just a phosphate team attached come a diacylglycerol does no qualify together a phospholipid. This would be taken into consideration a phosphatidate (diacylglycerol 3-phosphate), the precursor to phospholipids. Come qualify as a phospholipid, the phosphate group should be modified by one alcohol. Phosphatidylcholine and also phosphatidylserine are instances of two necessary phospholipids that are discovered in plasma membranes.

Phospholipid MoleculeA phospholipid is a molecule with two fat acids and also a amendment phosphate team attached to a glycerol backbone. The phosphate may be amendment by the enhancement of fee or polar chemical groups. Two chemical groups that might modify the phosphate, choline and serine, are presented here. Both choline and serine connect to the phosphate team at the place labeled R via the hydroxyl group indicated in green.

Structure of a Phospholipid Molecule

A phospholipid is one amphipathic molecule which method it has both a hydrophobic and a hydrophilic component. A single phospholipid molecule has actually a phosphate group on one end, called the “head,” and also two side-by-side chain of fat acids that comprise the lipid “tails. ” The phosphate team is negative charged, make the head polar and hydrophilic, or “water loving.” The phosphate heads are hence attracted to the water molecule in their environment.

The lipid tails, on the various other hand, are uncharged, nonpolar, and hydrophobic, or “water fearing.” A hydrophobic molecule repels and is repelled through water. Some lipid tails covers saturated fat acids and some save unsaturated fatty acids. This combination adds to the fluidity of the tails that space constantly in motion.

Phospholipids and also Biological Membranes

The cell membrane consists of two nearby layers the phospholipids, which kind a bilayer. The fatty acid tails of phospholipids face inside, away from water, vice versa, the phosphate heads confront the external aqueous side. Because the heads challenge outward, one layer is exposed to the internal of the cell and also one great is exposed to the exterior. Together the phosphate teams are polar and also hydrophilic, they room attracted to water in the intracellular fluid.

Phospholipid BilayerThe phospholipid bilayer is composed of two surrounding sheets the phospholipids, arranged tail to tail. The hydrophobic tails associate v one another, creating the inner of the membrane. The polar heads contact the fluid inside and outside the the cell.

Because the the phospholipds’ chemical and physical characteristics, the lipid bilayer acts as a semipermeable membrane; just lipophilic solutes can conveniently pass the phospholipd bilayer. As a result, there space two distinctive aqueous compartments on every side the the membrane. This separation is vital for many organic functions, consisting of cell communication and also metabolism.

Membrane Fluidity

A cell’s plasma membrane save proteins and other lipids (such as cholesterol) in ~ the phospholipid bilayer. Organic membranes continue to be fluid since of the unsaturated hydrophobic tails, which avoid phospholipid molecules from pack together and forming a solid.

If a fall of phospholipids are placed in water, the phospholipids spontaneously develops a structure well-known as a micelle, with their hydrophilic heads oriented towards the water. Micelles space lipid molecules the arrange themselves in a spherical form in aqueous solution. The development of a micelle is a response to the amphipathic nature of fat acids, an interpretation that they contain both hydrophilic and hydrophobic regions.

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MicellesAn example of micelles in water.

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