What makes lipids amphipathic

Waxes are valuable to both plants and animals because of their hydrophobic nature. This makes them water resistant, which prevents water from sticking on surfaces. Plant Waxes : Waxy coverings on some leaves are used as protective coatings. Unlike most natural waxes, which are esters, synthetic waxes consist of long-chain hydrocarbons lacking functional groups. Paraffin wax is a type of synthetic wax derived from petroleum and refined by vacuum distillation.

Synthetic waxes may also be obtained from polyethylene. Millions of of these waxes are produced annually, and they are used in adhesives, cosmetics, sealants and lubricants, insecticides, and UV protection. They are also used in foods like chewing gum. Generic structure formula of bee waxes : Ester myricyl palmitate is a major component of beeswax. Phospholipids are amphipathic molecules that make up the bilayer of the plasma membrane and keep the membrane fluid.

Phospholipids are major components of the plasma membrane, the outermost layer of animal cells. Like fats, they are composed of fatty acid chains attached to a glycerol backbone.

Unlike triglycerides, which have three fatty acids, phospholipids have two fatty acids that help form a diacylglycerol. The third carbon of the glycerol backbone is also occupied by a modified phosphate group. However, just a phosphate group attached to a diacylglycerol does not qualify as a phospholipid. This would be considered a phosphatidate diacylglycerol 3-phosphate , the precursor to phospholipids. To qualify as a phospholipid, the phosphate group should be modified by an alcohol.

Phosphatidylcholine and phosphatidylserine are examples of two important phospholipids that are found in plasma membranes. Phospholipid Molecule : A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone. The phosphate may be modified by the addition of charged or polar chemical groups. Two chemical groups that may modify the phosphate, choline and serine, are shown here. Both choline and serine attach to the phosphate group at the position labeled R via the hydroxyl group indicated in green.

A phospholipid is an amphipathic molecule which means it has both a hydrophobic and a hydrophilic component. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. This combination adds to the fluidity of the tails that are constantly in motion. The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer. The fatty acid tails of phospholipids face inside, away from water, whereas the phosphate heads face the outward aqueous side.

Since the heads face outward, one layer is exposed to the interior of the cell and one layer is exposed to the exterior. As the phosphate groups are polar and hydrophilic, they are attracted to water in the intracellular fluid. Phospholipid Bilayer : The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. The hydrophobic tails associate with one another, forming the interior of the membrane.

The polar heads contact the fluid inside and outside of the cell. As a result, there are two distinct aqueous compartments on each side of the membrane. This separation is essential for many biological functions, including cell communication and metabolism. Biological membranes remain fluid because of the unsaturated hydrophobic tails, which prevent phospholipid molecules from packing together and forming a solid.

If a drop of phospholipids is placed in water, the phospholipids spontaneously form a structure known as a micelle, with their hydrophilic heads oriented toward the water. Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solution.

The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic and hydrophobic regions.

Furthermore, it allows self-association and protein-protein interactions. Amphipathic helices are a common structural feature of proteins.

Examples of proteins with this conformation are ion channel membrane proteins, lung surfactant proteins, and apolipoproteins. Phospholipid is another amphipathic molecule. It is a type of lipid comprised of a glycerol bound to two fatty acids and a phosphate group. The glycerol with an attached negatively charged phosphate group is the hydrophilic head of a phospholipid.

The phosphate group may be further bound to hydrogen, choline, serine, ethanolamine, or inositol, thus, diversifying into phosphatidic acid, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and phosphatidylinositol phospholipids, respectively.

The two long fatty acid chains are the lipophilic hydrophobic tail of the phospholipid. The amphipathic nature of phospholipids made the latter an essential component of biological membranes. The plasma membrane, for instance, is largely made up of two layers of phospholipids. As amphipathic, phospholipids can interact with various molecules depending on polarity. The phospholipid heads interact readily with water and other polar molecules.

The phospholipid tails, in contrast, tend to avoid water and other polar interactions. Thus, phospholipids in water will aggregate by orienting their tails toward each other while exposing their heads to the aqueous environment. In fact, it is the amphipathic nature of phospholipids that help form the bilayer structure of the plasma membrane. The phospholipid tails orient themselves such that their tails line up internally of the plasma membrane while the phospholipid heads face the exterior.

Another amphiphile is cholesterol. It is made up of the hydrophilic hydroxyl group -OH and the hydrophobic bulky steroid and hydrocarbon chain. Cholesterol is found in the animal plasma membranes.

Its hydrophilic portion interacts with the aqueous medium and with the polar heads of the phospholipid. Its hydrophobic portion, in turn, is embedded in the membrane alongside the hydrophobic tails of the phospholipids and the nonpolar fatty acid chains of other lipids. Glycolipid s are amphipathic compounds since they are made up of hydrophilic sugar group s covalently linked to a hydrophobic lipid tail.

They are also present in the plasma membrane. The carbohydrate component extends to the cell exterior while the lipid component is embedded in the lipid bilayer. The sugar residues exposed to the exterior of the cell allow carbohydrate-carbohydrate interactions.

Bile acids have a steroid structure comprised of four rings and a side chain ending in a carboxylic acid and hydroxyl groups. Salts of bile acids can aggregate around the droplets of lipids and form micelles. When aggregated, they act as a surfactant. They emulsify lipids. This prevents fat droplets from aggregating into larger fat particles. Triacylgycerols are mostly carbon and hydrogen, giving them a predominently nonpolar character. The ester linkages of the molecule give it a somewhat polar end.

In contrast to the soaps discussed above, other lipids common in biological membranes have a larger van der Waals cross section and cannot approach one another close enough to form micelles. Instead, they spontaneously form a lipid bilayer. At right is shown the structural formula and cartoon versions of generic membrane phospholipids. A membrane phospholipid typically consists of a glycerol backbone, two fatty acid chains in ester linkages to glycerol, a phosphate diester linkage between glycerol and a number of possible alcohols ROH.

It is the presence of two nonpolar fatty acid chains in phospholipids in contrast to the single chain of soaps that favors bilayer over micelle formation for steric reasons.

The first fatty acid is of the saturated variety, while the second is typically an unsaturated fatty acid chain. The cis configuration of the latter confers a rigid kink in the chain, thus the first phospholipid cartoon is more stereochemically accurate, but the second cartoon is more suited to cartoon versions of bilayers and biological membranes. The existence of cells is obviously dependent on creation of a boundary that defines an inside compartment of controlled composition and character, and separates the cell from the surrounding uncontrolled environment.

Cellular membranes are topologically closed surfaces based upon phospholipid bilayers that perform this bounding function. Biological membranes act as physical barriers that generally limit the passage of charged and polar species, as well as the macromolecules central to living systems.

The amphipathic nature of phospholipids is responsible for the spontaneous formation of the bilayer structure of membranes. In aqueous media, these molecules assemble into a bilayer structure with the tails sequestered in a nonpolar interior, and heads interacting with polar solvent and solutes. There are many different lipids found in biological membranes, helping account for the different properties and functional roles membranes play in cellular biology.

The phospholipids are the largest proportion in most membranes, and consist of two types, the glycerophospholipids introduced above and the phosphocholine sphingolipids sphingomyelin. The glycerophospholipids can be considered derivatives of phosphatidate or phosphatidic acid in which it combines with other alcohols to form phosphatidyl esters, generating the variety of membrane lipids of this class.

Manabu Kitamata, Takehiko Inaba, Shiro Suetsugu; The roles of the diversity of amphipathic lipids in shaping membranes by membrane-shaping proteins. Biochem Soc Trans 30 June ; 48 3 : — Lipid compositions of cells differ according to cell types and intracellular organelles. Phospholipids are major cell membrane lipids and have hydrophilic head groups and hydrophobic fatty acid tails. The cellular lipid membrane without any protein adapts to spherical shapes, and protein binding to the membrane is thought to be required for shaping the membrane for various cellular events.

Until recently, modulation of cellular lipid membranes was initially shown to be mediated by proteins recognizing lipid head groups, including the negatively charged ones of phosphatidylserine and phosphoinositides.

Recent studies have shown that the abilities of membrane-deforming proteins are also regulated by the composition of fatty acid tails, which cause different degrees of packing defects. The binding of proteins to cellular lipid membranes is affected by the packing defects, presumably through modulation of their interactions with hydrophobic amino acid residues. Therefore, lipid composition can be characterized by both packing defects and charge density. The lipid composition regarding fatty acid tails affects membrane bending via the proteins with amphipathic helices, including those with the ArfGAP1 lipid packing sensor ALPS motif and via membrane-deforming proteins with structural folding, including those with the Bin—Amphiphysin—Rvs BAR domains.

This review focuses on how the fatty acid tails, in combination with the head groups of phospholipids, affect protein-mediated membrane deformation. Sign In or Create an Account. Advanced Search.