This is a dehydration synthesis reaction. Saturated fatty acids have all neighboring carbons in the hydrocarbon chain linked by single covalent bonds. This maximizes the number of hydrogen atoms attached to the carbon skeleton. Then, we say that carbons in the chain are saturated with hydrogens. Unsaturated fatty acids have at least two neighboring carbons in the hydrocarbon chain linked by double covalent bonds.
This does not allow all carbons in the chain to maximize the number of hydrogen atoms attached to the carbon skeleton. Then, carbons in the chain are unsaturated or not saturated with hydrogens. Most triglycerides made of unsaturated fatty acids are liquid and are called oils. Triglycerides made of saturated fatty acids are semisolid at room temperature e. 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. Phosphatidalcholine, the plasmalogen related to phosphatidylcholine, is abundant in the heart muscle. Another structures related to phospholipids are sphingolipids. In these structures glycerol is replaced by the amino alcohol; sphingosine. When the hydroxyl group alcoholic group of sphingosine is substituted by phosphocholine, it is formed sphingomyelin, which is the only sphingolipid that is present in significant amount in human tissues as a constituent of myelin that forms nerve fibers [ref].
Platelet activating factor PAF is an unusual glycerophospholipid structure. In this molecule position sn-1 of glycerol is linked to a saturated alcohol through an ether bond such as in plasmalogens and at the sn-2 binds an acetyl group instead of a fatty acid.
PAF is released by a variety of cells and by binding to membrane receptors produces aggregation and degranulation of platelets, has potent thrombotic and inflammatory effects, and is a mediator of anaphylactic reactions [ 55 ].
Structure of various phospholipids. A fundamental aspect of phospholipids is their participation in the structure of biological membranes, and the structural characteristics of the fatty acids are relevant to determine the behavior and the biological properties of the membrane. As an example, a diet rich in saturated fatty acids result in an increase in the levels of these fatty acids into cell membrane phospholipids, causing a significant decrease in both, membrane fluidity and in the ability of these structure to incorporate ion channels, receptors, enzymes, structural proteins, etc.
At the nutritional and metabolic level this effect is highly relevant because as the fatty acid composition of the diet is directly reflected into the fatty acid composition of phospholipids, changes in the composition of the diet, i. Figure 8 shows a simulation how the structural differences of the fatty acids which comprise phospholipids may affect the physical and chemical behavior of a membrane.
Sterols are derived from a common structural precursor, the sterane or cyclopentanoperhydrophenanthrene, consisting in a main structure formed by four aromatic rings identified as A, B, C and D rings. All sterols have at carbon 3 of A ring a polar hydroxyl group being the rest of the structure non-polar, which gives them certain amphipathic character, such as phospholipids.
Sterols have also a double bound at carbons 5 and 6 of ring B [ 58 ]. This double bond can be saturated reduced which leads to the formation of stanols, which together with plant sterols derivatives are currently used as hypocholesterolemic agents when incorporated into some functional foods. At carbon 17 ring D both sterols as stanols have attached an aliphatic group, consisting in a linear structure of 8, 9 or 10 carbon atoms, depending on whether the sterol is from animal origin 8 carbon atoms or from vegetable origin 9 or 10 carbon atoms [ 59 ].
Figure 9 shows the structure of cyclopentanoperhydrophenanthrene and cholesterol. Often sterols, and less frequent stanols, have esterified the hydroxyl group of carbon 3 ring A with a saturated fatty acid usually palmitic; C or unsaturated fatty acid most frequent oleic; C and less frequent linoleic acid; C The esterification of the hydroxyl group eliminates the anphipaticity of the molecule and converts it into a structure completely non-polar.
Undoubtedly among sterols cholesterol is the most important because it is the precursor of important animal metabolic molecules, such as steroid hormones, bile salts, vitamin D, and oxysterols, which are oxidized derivatives of cholesterol formed by the thermal manipulation of cholesterol and that have been identified as regulators of the metabolism and homeostasis of cholesterol and sterols in general [ 60 ].
Simulation how the structural differences of the fatty acids which comprise phospholipids may affect the physical and chemical behavior of a membrane. Structure of cyclopentanoperhydrophenanthrene and cholesterol. Lipids are a large and wide group of molecules that are present in all living organism and also in foods and characterized by particular physicochemical properties, such as their non polarity and their solubility in organic solvents.
Some lipids, in particular fatty acids and sterols, are essential for animal and plant life. Lipids are key elements in the structure, biochemistry, physiology, and nutritional status of an individual, because are involved in: i the cellular structure; ii the cellular energy reserve, iii the formation of regulatory metabolites, and; iv in the regulation and gene expression, which directly affects the functioning of the body.
Structural and functional characteristics of lipids, discussed in this chapter, will allow you to integrate those metabolic aspects of these important and essential molecules in close relationship of how foods containing these molecules can have a relevant influence in the health or illness of an individual.
Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers.
Login to your personal dashboard for more detailed statistics on your publications. Edited by Rodrigo Valenzuela Baez. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Introduction The term lipid is used to classify a large number of substances having very different physical - chemical characteristics, being its solubility in organic non-polar solvents the common property for their classification.
Think about It Explain why fatty acids with hydrocarbon chains that contain only single bonds are called saturated fatty acids. Think about It How is the amphipathic nature of phospholipids significant? This video provides additional information about phospholipids and liposomes:. Think about It How are isoprenoids used in technology? Key Concepts and Summary Lipids are composed mainly of carbon and hydrogen, but they can also contain oxygen, nitrogen, sulfur, and phosphorous.
They provide nutrients for organisms, store carbon and energy, play structural roles in membranes, and function as hormones, pharmaceuticals, fragrances, and pigments. Fatty acids are long-chain hydrocarbons with a carboxylic acid functional group.
Their relatively long nonpolar hydrocarbon chains make them hydrophobic. Fatty acids with no double bonds are saturated ; those with double bonds are unsaturated. Fatty acids chemically bond to glycerol to form structurally essential lipids such as triglycerides and phospholipids.
Triglycerides comprise three fatty acids bonded to glycerol, yielding a hydrophobic molecule. Phospholipids contain both hydrophobic hydrocarbon chains and polar head groups, making them amphipathic and capable of forming uniquely functional large scale structures.
Biological membranes are large-scale structures based on phospholipid bilayers that provide hydrophilic exterior and interior surfaces suitable for aqueous environments, separated by an intervening hydrophobic layer.
These bilayers are the structural basis for cell membranes in most organisms, as well as subcellular components such as vesicles. Isoprenoids are lipids derived from isoprene molecules that have many physiological roles and a variety of commercial applications.
A wax is a long-chain isoprenoid that is typically water resistant; an example of a wax-containing substance is sebum, produced by sebaceous glands in the skin. Steroids are lipids with complex, ringed structures that function as structural components of cell membranes and as hormones.
Bacteria produce hopanoids, structurally similar to cholesterol, to strengthen bacterial membranes. Fungi and protozoa produce a strengthening agent called ergosterol. Multiple Choice Which of the following describes lipids?
All of the options describe lipids. Show Answer Answer b. Molecules bearing both polar and nonpolar groups are amphipathic. Show Answer False. In the ancient world, soap was made by first boiling rainwater with ashes from burnt wood to produce lye: a very basic, or alkaline, solution high pH see our Acids and Bases: An Introduction module. Next, this solution was combined with animal fat or vegetable oil and cooked over a low fire for many hours until the mixture changed into a gel.
The fundamental procedure of this chemical reaction, now called saponification , is still used today to make soap. The first steps toward understanding lipids were taken in the early s by a young French scientist named Michel Chevreul Chevreul began his career in the laboratory of Louis Vauquelin, where his role was to use various solvents such as water, alcohol , and ether to separate the colored dye pigments from natural products like vegetable oils, waxes, tree gums, and resins.
At the end of each experiment , Chevreul would wash out the glassware using a lot of soap. While conducting his research , Chevreul observed that if he accidentally left soapy water in some glassware and it evaporated overnight, salt crystals would be left behind.
He was confused by this because he had added only water or another solvent and soap to the glassware. It raised the question: Where was the salt coming from? Through deductive reasoning, Chevreul realized it must be the result of the soap. When he learned how soap was made by mixing animal or vegetable fat with alkali water, though, he was still confused because there was no salt in that process either.
Intrigued and persistent, Chevreul went on to study the process of soap-making in his own laboratory. As he made various kinds of soap, he observed that as oils react with the alkali water, they turn from a translucent liquid into a thick, milky pudding, which gradually hardens. At the time, he knew that oils and fats contain large amounts of carbon and hydrogen and only small amounts of oxygen. He hypothesized that the reaction with the alkali solution , which had a high pH and thus a higher concentration of hydroxide ions OH - , was somehow adding oxygen atoms to the structure of the fats to change them from pure hydrocarbons to molecules with some salt-like properties.
This was an excellent hypothesis because it would explain two different phenomena at the same time. First, it explained the salt crystals left when soapy water dries. Second, it explained why soap is soluble in both water and oil. The hydrocarbons from the fat would still be oil-soluble, but their new salt-like properties, coming from the added oxygen atoms , would allow them to be soluble in water, a property that all salts have.
Although it took him most of his career to do it, Chevreul demonstrated that his hypothesis was correct. He did this by performing painstaking chemical analyses of various fats, oils, and the soaps that are produced when alkali is added to them.
Chevreul discovered that, during saponification , some of the hydroxide OH - ions from the alkali solution are indeed added to the hydrocarbons from the fats. When this happens, some chemical bonds in the fat molecules are broken, releasing long-tailed fatty acids Figure 2. Many of the names of common fatty acids that we use today were given to these molecules by Chevreul Cistola et al. The reason that hydrocarbon tails from fats are not soluble in water is because almost all of the bonds are symmetrical and thus nonpolar.
However, when the hydroxide ions break the ester group in fat molecules during saponification , a charged and polar group is created — a carboxylic acid group — which is very soluble in water. These fatty acids have a very special structure. They have long chains of nonpolar bonds , which makes them easily dissolvable in oil and grease; but they also have a polar charged group at one end, which makes them easily dissolvable in water.
Thus, these molecules have a dual nature — they are both water-soluble hydrophilic, "loves water" and oil-soluble lipophilic, "loves fat". The word for this is amphiphilic , which means "loves both. What Chevreul and others showed was that an alkali solution breaks up the fat molecules and two parts are released: glycerol and fatty acids.
We now know the complete structure of the fat molecule Figure 3. During the process of saponification , the hydroxide ions in the alkali solution "attack" the ester group and thus release the fatty acid chains from the glycerol backbone.
Chevreul was able to figure this out by analyzing the chemical composition of the fats before the reaction , and then repeating the analysis with the fatty acids that resulted.
He did this again and again with different kinds of fats, which made slightly different kinds of soaps. The result was the common theme that fats are made of glycerol and fatty acids. Animals and plants use fats and oils to store energy.
As a general rule, fats come from animals and oils come from plants. Because of slight differences in structure, fats are solid at room temperature and oils are liquid at room temperature. However, both fats and oils are called triglycerides because they have three fatty acid chains attached to a glycerol molecule , as shown in Figure 3. The carbon-hydrogen bonds abbreviated C-H found in the long tails of fatty acids are high-energy bonds.
Thus, triglycerides make excellent storage forms of energy because they pack many high-energy C-H bonds into a compact structure of three tightly packed fatty acid tails. For this reason, dietary fats and oils are considered "calorie dense.
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