Biochemistry of Lipids: Fatty Acids, Omega Fats, Triglycerides, Phospholipids, Eicosanoids
In biology and biochemistry, a lipid is a biomolecule that is soluble in nonpolar solvents. Lipids also encompass molecules such as fatty acids and their derivatives (including tri-, di- .. None of these studies suggested any connection between percentage of calories from fat and risk of cancer, heart disease, or weight gain. The main difference between lipids and fats is that lipids are a broad group . Based on the degree of saturation of the fatty acid molecules, two. The difference between fatty acid compositions of marine and freshwater fish has been noted by several authors. Some examples of fatty acid patterns are given.
When the hydrocarbon chain has a double bond, the fatty acid is said to be unsaturated, as it now has fewer hydrogens. The double bonds in unsaturated fatty acids, like other types of double bonds, can exist in either a cis or a trans configuration.
In the cis configuration, the two hydrogens associated with the bond are on the same side, while in a trans configuration, they are on opposite sides see below. A cis double bond generates a kink or bend in the fatty acid, a feature that has important consequences for the behavior of fats. Saturated fatty acid example: Unsaturated fatty acid examples: Saturated fatty acids tails are straight, so fat molecules with fully saturated tails can pack tightly against one another. This tight packing results in fats that are solid at room temperature have a relatively high melting point.
In contrast, cis-unsaturated fatty acid tails are bent due to the cis double bond. This makes it hard for fat molecules with one or more cis-unsaturated fatty acid tails to pack tightly.
So, fats with unsaturated tails tend to be liquid at room temperature have a relatively low melting point — they are what we commonly call oils. For instance, olive oil is mostly made up of unsaturated fats 2 2. Trans fats are rare in nature, but are readily produced in an industrial procedure called partial hydrogenation. In this process, hydrogen gas is passed through oils made mostly of cis-unsaturated fatsconverting some — but not all — of the double bonds to single bonds.
Trans-unsaturated fatty acids can pack more tightly and are more likely to be solid at room temperature. Partial hydrogenation and trans fats might seem like a good way to get a butter-like substance at oil-like prices. Unfortunately, trans fats have turned out to have very negative effects on human health. Because of a strong link between trans fats and coronary heart disease, the U.
Food and Drug Administration FDA recently issued a ban on trans fats in foods, with a three-year deadline for companies to remove trans fats from their products 4 4. Omega fatty acids Another class of fatty acids that deserves mention includes the omega-3 and omega-6 fatty acids.
There are different types of omega-3 and omega-6 fatty acids, but all of them are made from two basic precursor forms: Some fish, such as salmon, and some seeds, such as chia and flax, are good sources of omega-3 fatty acids.
Omega-3 and omega-6 fatty acids have at least two cis-unsaturated bonds, which gives them a curved shape. What makes a fatty acid omega-3 or omega-6? The naming of these molecules is based on their structure. Omega-6 fatty acids are defined analogously, with the first double bond located between the sixth and seventh carbons from the omega end. Image of alpha-linoleic acid ALAshowing its curled shape due to its three cis double bonds.
Omega-3 and omega-6 fatty acids play a number of different roles in the body.
They are precursors starting material for the synthesis of a number of important signaling molecules, including ones that regulate inflammation and mood.
Omega-3 fatty acids in particular may reduce the risk of sudden death from heart attacks, decrease triglycerides in the blood, lower blood pressure, and prevent the formation of blood clots. However, fats are essential to the body and have a number of important functions. For instance, many vitamins are fat-soluble, meaning that they must be associated with fat molecules in order to be effectively absorbed by the body.
Fats also provide an efficient way to store energy over long time periods, since they contain over twice as much energy per gram as carbohydrates, and they additionally provide insulation for the body. Like all the other large biological molecules, fats in the right amounts are necessary to keep your body and the bodies of other organisms functioning correctly. Waxes Waxes are another biologically important category of lipids.
Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants, where its hydrophobic water-repelling properties prevent water from sticking to, or soaking into, the surface. Image of shiny leaf surface covered with wax. However if they are saturated fats without single bonds, they do not smell. Fatty acids with cis double bonds are liquids, although hydrogenation can turn them into solids by turning them into saturated fatty acids. Cis fatty acids have "kinks" in them and hence do not pack well, so they remain in a liquid state at lower temperatures.
Saturated fatty acids, however, have straight carbon chains that pack well, which enables them to solidify up to higher temperatures. The methods of hydrogenation of fats were developed in early s for the purpose of developing solid fats for making soaps. Later they were used to hydrogenate dietary fatty acids such as soybean oils because hydrogenated oils do not go rancid and smell.
Slowly, they got into baked goods and candies. And now-a-days, it is difficult to find any packaged foods or snacks without Trans fats. Hydrogenation removes double bonds and not covert cis fatty acids to Trans fatty acid which also contain double bonds. This leads to the process of hydrogenation: While there are many modification to it, the major process is to heat the unsaturated oils to above 0C, add powdered nickel as catalyst bubble hydrogen through it.
The double bonds get saturated. However all the double bonds do not get saturated. And at that high temperature some of the double bonds seem to migrate to other carbons in the chain. Formation of trans configuration is more stable than cis. In that process at the newer position they become trans double bond. Cis configuration has more strain in it than trans. Why are partially hydrogenated or trans fats bad for health? As mentioned above, our body mostly contains cis fatty acids.
Whether our cells make them or they are from natural diet sources, they are all of cis configuration. Since all the natural fats are cis, the cellular enzymes have active sites that preferentially metabolize cis fatty acids. So over several years, trans fats accumulate in the body over those of cis form. Since all the natural fatty acids are cis, the enzymes that synthesize triglycerides and the enzymes that breakdown fats for energy, may not work efficiently.
In addition as the trans fats accumulate in the body, as they are similar in structure to cis fats to an extent they mat act as competitive inhibitors to fatty acid metabolizing enzymes.
In addition, when natural cis fatty acids are incorporated into the cell membranes, as they have cis configuration, they do not pack very compact thus giving fluidity to the cell membrane. If membranes contain trans fats in them, the membrane fluidity will be affected. It is also likely that membrane receptor function will also be affected. If the Trans fatty acids are incorporated into erythrocyte membranes, the membranes would be more rigid and erythrocytes would break as they travel through the microcapillaries.
Introduction to fatty acids and lipids.
Conclusions based on clinical studies[ edit ] Women with high levels of trans fat in their bloodstreams had three times the risk of developing heart disease as women with the lowest levels of these kinds of fats. C-reactive protein CRP is made by the liver. Its levels in the blood are indicators of inflammation. A 6 year study, monkeys fed with trans fats gained 7.
Lipids (article) | Macromolecules | Khan Academy
Biological Presence[ edit ] Fatty acids in biological systems usually contain an even number of carbon atoms, typically between 14 and 24, although the and carbon fatty acids are the most abundant. Fatty acids typically contain an even number of carbon atoms because of the way in which fatty acids are biosynthesized.
Animal fatty acids have hydrocarbon chains which are almost invariably un-branched. The alkyl chain may be saturated or it may contain one or more double bonds. In most unsaturated fatty acids, the double bonds are in the cis formation.
The double bonds in polyunsaturated fatty acids, though, are generally separated by at least one methylene group. The chain length and degree of saturation give way to the properties that are found within the fatty acids and lipids.
Unsaturated fatty acids have lower melting points than saturated fatty acids of the same length. Because double bonds cause the hydrocarbon chain to bend. Therefore, the fatty acids cannot compact tightly together, reducing the van der Waals interaction between the fatty acids. The melting point of fatty acids is also affected by chain length.
The longer the hydrocarbon chain is, the higher the melting point. Short chain length and unsaturation enhance the fluidity of fattty acids and of their derivatives. Animals take advantage of this fatty acid property to maintain the fluidity of their cell membranes.
When the weather turns cold, animals have an enzyme that converts saturated fatty acid to unsaturated fatty acid with one or more unsaturation. This prevents the membrane from getting frozen by lowering the melting point of the fatty acids in the membrane.
Fatty acids can also form structures known as micelles in an aqueous solution. The structure is formed when the hydrocarbon tails form a hydrophobic center, while the polar heads form a hydrophilic shell outside the interior. The significance of micelles is that they act as emulsifiers, thus dissolving fat-soluble vitamins or other lipids that need to be absorbed. Essential Fatty Acids[ edit ] There are two fatty acids that the body cannot produce; all of the others can be derived from other molecules.
Those two essential fatty acids are linoleic acid and alpha-linoleic acid. Luckily, these two can be found easily in most plant and animal oils. Other fatty acids such as omega-3 fatty acids can be produced by the body, but it is easier to get these from diet.Lipids
Some sources are fish oils. These fatty acids are used to help with essential body functions such as blood clotting, immune response, or blood pressure. They help make important fatty acids such as eicosanoids. Eicosanoids are important signaling molecules in the body. They are derived from C chains derived from such molecules as the previously stated omega-3 fatty acids. Eicosanoids participate in activities such as relaying messages in the central nervous system or helping in the inflammatory response.
Other important Fatty Acids[ edit ] Nutritional Significance[ edit ] Fatty acids are significant in the nutrition of living organisms, because of the cell membrane's integral structure built up of fatty acids. Fats can be found in different quantities of various foods. While obesity is becoming a large issue in society today, the reviewing of types of fats and how they affect our bodies is a growing concern.
Introduction to fatty acids and lipids.
Trans fatty acids are a large part of this concern. Trans fatty acids are fats found in foods such as some cookies, processed foods, crackers, candy, baked goods, fried foods, and other similar items. They are a concern to our health because studies have shown that diets high in trans fats increase the risk of various diseases including heart disease.
The trans fats can be related to the levels of LDL cholesterol. Trans fats are found in ingredients labeled as shortening, and hydrogenated oil. While fatty acids are an important part of living, they can be classified as "good" and "bad" fats. Bad fats are those that have negative effects on cholesterol levels. Bad fats are trans and saturated fatty acids. Good fats are those that have positive effects on cholesterol levels. Good fats consist of poly and monounsaturated fatty acids.
Foods such as olive oil, soybean oil, and other vegetable derived oils are usually included. Isolation and Identification[ edit ] The structure of a known acid can be defined by using gas chromatography, comparing the acid with an authentic sample or with compounds of related structure.
However, if the fatty acid is completely unknown, spectroscopic procedures will be needed in order to provide more evidence. In order to determine the structure of a fatty acid you must know the chain length and the components of the structure such as branched or cyclic or other functional groups. You must also know the configuration, position, number and nature of the unsaturated centers and also the nature and position of the functional groups.
Thin-Layer Chromatography TLC [ edit ] Used more for a qualitative comparison, TLC separates compounds with different polarities based off their attraction to the solvent mobile phase which moves up the TLC plate stationary phase. The compounds have the choice to either react with either phase, which usually have different polar properties.
The stationary phase is usually polar silica gel which ties up any of the more polar molecules, essentially slowing their movement up the plate, while the mobile phase is usually of lower polarity to move the less polar compounds father up the plate.
Although thin-layer chromatography doesn't separate acids that differ only in chain length or degree of unsaturation, it is still useful in separating acids or esters with additional polar groups. If the silica layer is altered, then other separations can be achieved.
This separates the acids based on the number of double bonds that they have. By using a column with a thin internal diameter, coupled with a high pressured eluent to force the sample through the column, HPLC obtains a higher degree of separation than gravity powered chromatography. Gas Chromatography[ edit ] Gas chromatography using capillary columns are now one of the most commonly used methods in separating methyl esters.
By studying the elution out of the capillary column, chain length, degree of unsaturation, and the position of unsaturated centers can be identified. Biosynthesis of Fatty Acids[ edit ] Understanding the biosynthesis of fatty acids will give you information about the chemical pathway of the fatty acid, the enzymes that are involved in each step of the biosynthesis, the regulatory procedures, and where these reactions occur in the plant, animal, or micro-organism.
- Structural Biochemistry/Lipids/Fatty Acids
The five major biosynthetic pathways are: Presumably decarboxylation gives an enol, which attacks the acetyl group. The ketone carbonyl of the acetoacetyl group is reduced to an alcohol function. One is half derived from the original methyl carbon while the other half is derived from the carboxyl carbon atom. Because fatty acids tend to be derived from C2 atoms explain why fatty acids almost always contain an even number of carbons.
Malonate is more reactive than acetate and it is produced from acetate and carbon dioxide. Despite the involvement of malonate, it does not appear in the final product and all of the carbon atoms in the fatty acids come from acetate.