Which members of the lipid family are non essential

Sphingolipids are a complex family of compounds that share a common structural feature, a sphingoid base backbone that is synthesized de novo from serine and a long-chain fatty acyl-CoA, then converted into ceramides, phosphosphingolipids, glycosphingolipids, and other species, including protein adducts.

A number of organisms also produce sphingoid base analogs that have many of the same features as sphingolipids such as long-chain alkyl and vicinal amino and hydroxyl groups but differ in other features. These have been included in this category because some are known to function as inhibitors or antagonists of sphingolipids, and in some organisms, these types of compounds may serve as surrogates for sphingolipids.

Sphingolipids can be divided into several major classes: the sphingoid bases and their simple derivatives such as the 1-phosphate , the sphingoid bases with an amide-linked fatty acid e. The major sphingoid base of mammals is commonly referred to as "sphingosine," because that name was affixed by the first scientist to isolate this compound.

Sphingosine is 2S,3R,4E aminooctadecene-1,3-diol it is also called D-erythro-sphingosine and sphingenine. This is only one of many sphingoid bases found in nature, which vary in alkyl chain length and branching, the number and positions of double bonds, the presence of additional hydroxyl groups, and other features.

Sphingoid bases are found in a variety of derivatives, including the 1-phosphates, lysosphingolipids such as sphingosine 1-phosphocholine as well as sphingosine 1-glycosides , and N-methyl derivatives N-methyl, N,N-dimethyl, and N,N,N-trimethyl. In addition, a large number of organisms, such as fungi and sponges, produce compounds with structural similarity to sphingoid bases, some of which such as myriocin and the fumonisins are potent inhibitors of enzymes of sphingolipid metabolism.

Ceramides N-acyl-sphingoid bases are a major subclass of sphingoid base derivatives with an amide-linked fatty acid. The fatty acids are typically saturated or monounsaturated with chain lengths from 14 to 26 carbon atoms; the presence of a hydroxyl group on carbon 2 is fairly common. Ceramides sometimes have specialized fatty acids which has a 30 carbon fatty acid with a hydroxyl group on the terminal carbon.

Ceramides are generally precursors of more complex sphingolipids. The major phosphosphingolipids of mammals are sphingomyelins ceramide phosphocholines , whereas insects contain mainly ceramide phosphoethanolamines and fungi have phytoceramidephosphoinositols and mannose-containing head groups. Glycosphingolipids are classified on the basis of carbohydrate composition: 1 neutral glycosphingolipids contain one or more uncharged sugars such as glucose Glu , galactose Gal , N-acetylglucosamine GlcNAc , N-acetylgalactosamine GalNAc , and fucose Fuc , which are grouped into families based on the nature of the glyco- substituents as shown in the listing; 2 acidic glycosphingolipids contain ionized functional groups phosphate or sulfate attached to neutral sugars or charged sugar residues such as sialic acid N-acetyl or N-glycoloyl neuraminic acid.

The latter are called gangliosides, and the number of sialic acid residues is usually denoted with a subscript letter i. For a few glycosphingolipids, historically assigned names as antigens and blood group structures are still in common use e.

Some aquatic organisms contain sphingolipids in which the phosphate is replaced by a phosphono or arsenate group. The other category includes sphingolipids that are covalently attached to proteins; for example, -hydroxyceramides and -glucosylceramides are attached to surface proteins of skin, and inositol-phosphoceramides are used as membrane anchors for some fungal proteins in a manner analogous to the glycosylphosphatidylinositol anchors that are attached to proteins in other eukaryotes.

Sterol lipids, such as cholesterol and its derivatives are an important component of membrane lipids,[8] along with the glycerophospholipids and sphingomyelins. The steroids, which also contain the same fused four-ring core structure, have different biological roles as hormones and signaling molecules.

The C18 steroids include the estrogen family whereas the C19 steroids comprise the androgens such as testosterone and androsterone. The C21 subclass includes the progestogens as well as the glucocorticoids and mineralocorticoids. The secosteroids, comprising various forms of vitamin D, are characterized by cleavage of the B ring of the core structure.

Other examples of sterols are the bile acids and their conjugates,[9] which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver. Prenol lipids are synthesized from the 5-carbon precursors isopentenyl diphosphate and dimethylallyl diphosphate that are produced mainly via the mevalonic acid MVA pathway.

Structures containing greater than 40 carbons are known as polyterpenes. Carotenoids are important simple isoprenoids that function as anti-oxidants and as precursors of vitamin A. Another biologically important class of molecules is exemplified by the quinones and hydroquinones, which contain an isoprenoid tail attached to a quinonoid core of non-isoprenoid origin.

Vitamin E and vitamin K, as well as the ubiquinones, are examples of this class. Bacteria synthesize polyprenols called bactoprenols in which the terminal isoprenoid unit attached to oxygen remains unsaturated, whereas in mammalian polyprenols dolichols the terminal isoprenoid is reduced. Saccharolipids describe compounds in which fatty acids are linked directly to a sugar backbone, forming structures that are compatible with membrane bilayers.

In the saccharolipids, a sugar substitutes for the glycerol backbone that is present in glycerolipids and glycerophospholipids. The most familiar saccharolipids are the acylated glucosamine precursors of the Lipid A component of the lipopolysaccharides in Gram-negative bacteria.

Typical lipid A molecules are disaccharides of glucosamine, which are derivatized with as many as seven fatty-acyl chains. The minimal lipopolysaccharide required for growth in E. Polyketides are synthesized by polymerization of acetyl and propionyl subunits by classic enzymes as well as iterative and multimodular enzymes that share mechanistic features with the fatty acid synthases.

They comprise a very large number of secondary metabolites and natural products from animal, plant, bacterial, fungal and marine sources, and have great structural diversity. Many commonly used anti-microbial, anti-parasitic, and anti-cancer agents are polyketides or polyketide derivatives, such as erythromycins, tetracylines, avermectins, and antitumor epothilones. Eukaryotic cells are compartmentalized into membrane-surrounded organelles which carry out a variety of biological functions.

The glycerophospholipids are the main structural component of biological membranes, such as the plasma membrane of cells and the intracellular membranes of organelles; in mamalian cells the plasma membrane physically separates the intracellular components from the extracellular environment.

The glycerophospholipids are amphipathic molecules containing both hydrophobic and hydrophilic regions that contain a glycerol core linked to two fatty acid-derived "tails" by ester linkages and to one "head" group by a phosphate ester linkage. While glycerophospholipids are the major component of biological membranes, other non-glyceride lipid components such as sphingomyelin and sterols mainly cholesterol in mamalian cell membranes are also found in biological membranes. In plants and algae, the galactosyldiacylglycerols, and sulfoquinovosyldiacylglycerol, which lack a phosphate group, are important components of membranes of chloroplasts and related organelles and are the most abundant lipids in photosynthetic tissues, including those of higher plants, algae and certain bacteria.

The three fatty acids in the triacylglycerol may be similar or dissimilar. Fats are also called triacylglycerols or triglycerides because of their chemical structure. Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid , is derived from the palm tree.

Arachidic acid is derived from Arachis hypogea, the scientific name for groundnuts or peanuts. Fatty acids may be saturated or unsaturated. In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is said to be saturated. Saturated fatty acids are saturated with hydrogen; in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized.

Stearic acid is an example of a saturated fatty acid Figure 3. When the hydrocarbon chain contains a double bond, the fatty acid is said to be unsaturated. Oleic acid is an example of an unsaturated fatty acid Figure 4. Most unsaturated fats are liquid at room temperature and are called oils. If there is one double bond in the molecule, then it is known as a monounsaturated fat e. When a fatty acid has no double bonds, it is known as a saturated fatty acid because no more hydrogen may be added to the carbon atoms of the chain.

A fat may contain similar or different fatty acids attached to glycerol. Long straight fatty acids with single bonds tend to get packed tightly and are solid at room temperature. Animal fats with stearic acid and palmitic acid common in meat and the fat with butyric acid common in butter are examples of saturated fats.

In plants, fat or oil is stored in many seeds and is used as a source of energy during seedling development. Unsaturated fats or oils are usually of plant origin and contain cis unsaturated fatty acids. Cis and trans indicate the configuration of the molecule around the double bond.

If hydrogens are present in the same plane, it is referred to as a cis fat; if the hydrogen atoms are on two different planes, it is referred to as a trans fat. Olive oil, corn oil, canola oil, and cod liver oil are examples of unsaturated fats. Unsaturated fats help to lower blood cholesterol levels whereas saturated fats contribute to plaque formation in the arteries. Figure 5. Saturated fatty acids have hydrocarbon chains connected by single bonds only.

Unsaturated fatty acids have one or more double bonds. Each double bond may be in a cis or trans configuration. In the cis configuration, both hydrogens are on the same side of the hydrocarbon chain. In the trans configuration, the hydrogens are on opposite sides. A cis double bond causes a kink in the chain. In the food industry, oils are artificially hydrogenated to make them semi-solid and of a consistency desirable for many processed food products. Simply speaking, hydrogen gas is bubbled through oils to solidify them.

During this hydrogenation process, double bonds of the cis — conformation in the hydrocarbon chain may be converted to double bonds in the trans — conformation. Margarine, some types of peanut butter, and shortening are examples of artificially hydrogenated trans fats.

This unique structure makes phospholipids water soluble. Phospholipids are what we call amphiphilic—the fatty-acid sides are hydrophobic dislike water and the phosphate group is hydrophilic likes water.

In the body phospholipids bind together to form cell membranes. The amphiphilic nature of phospholipids governs their function as components of cell membranes. The phospholipids form a double layer in cell membranes, thus effectively protecting the inside of the cell from the outside environment while at the same time allowing for transport of fat and water through the membrane.

Phospholipids are ideal emulsifiers that can keep oil and water mixed. Emulsions are mixtures of two liquids that do not mix. Without emulsifiers, the fat and water content would be somewhat separate within food. Lecithin phosphatidylcholine , found in egg yolk, honey, and mustard, is a popular food emulsifier. Food emulsifiers play an important role in making the appearance of food appetizing. Adding emulsifiers to sauces and creams not only enhances their appearance but also increases their freshness.

Many people attribute health-promoting properties to lecithin, such as its ability to lower blood cholesterol and aid with weight loss. Cholesterol is also the precursor to bile salts, which help in the emulsification of fats and their absorption by cells. It is a component of the plasma membrane of animal cells and the phospholipid bilayer. Being the outermost structure in animal cells, the plasma membrane is responsible for the transport of materials and cellular recognition; and it is involved in cell-to-cell communication.

Thus, steroids also play an important role in the structure and function of membranes. It has also been discovered that steroids can be active in the brain where they affect the nervous system, These neurosteroids alter electrical activity in the brain.

They can either activate or tone down receptors that communicate messages from neurotransmitters. Since these neurosteroids can tone down receptors and decrease brain activity, steroids are often used in anesthetic medicines. Privacy Policy. Skip to main content. Biological Macromolecules. Search for:. Lipid Molecules Fats and oils, which may be saturated or unsaturated, can be unhealthy but also serve important functions for plants and animals. Learning Objectives Differentiate between saturated and unsaturated fatty acids.

Key Takeaways Key Points Fats provide energy, insulation, and storage of fatty acids for many organisms. Fats may be saturated having single bonds or unsaturated having double bonds. Unsaturated fats may be cis hydrogens in same plane or trans hydrogens in two different planes. Olive oil, a monounsaturated fat, has a single double bond whereas canola oil, a polyunsaturated fat, has more than one double bond.

Omega-3 fatty acid and omega-6 fatty acid are essential for human biological processes, but they must be ingested in the diet because they cannot be synthesized. Key Terms hydrogenation : The chemical reaction of hydrogen with another substance, especially with an unsaturated organic compound, and usually under the influence of temperature, pressure and catalysts. It contains the functional group carbon-oxygen double bond joined via carbon to another oxygen atom. OH ; characteristic of carboxylic acids.

Waxes Waxes are nonpolar lipids that plants and animals use for protection and have many functions in society. Learning Objectives Describe the roles played by waxes. Key Takeaways Key Points Natural waxes are typically esters of fatty acids and long chain alcohols. Animal wax esters are derived from a variety of carboxylic acids and fatty alcohols. Plant waxes are derived from mixtures of long-chain hydrocarbons containing functional groups.

Because of their hydrophobic nature, waxes prevent water from sticking on plants and animals. Synthetic waxes are derived from petroleum or polyethylene and consist of long-chain hydrocarbons that lack functional groups. Synthetic and waxes are used in adhesives, cosmetics, food, and many other commercial products. Key Terms paraffin wax : A waxy white solid hydrocarbon mixture used to make candles, wax paper, lubricants, and sealing materials.

Phospholipids Phospholipids are amphipathic molecules that make up the bilayer of the plasma membrane and keep the membrane fluid. Learning Objectives Describe phospholipids and their role in cells. Key Takeaways 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.