Which elements mainly comprise lipids

The most common number of carbons in the fatty acid chain ranges from 12 to 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. What is UREX? What are the four categories of biochemical molecules of the human body? What are some common mistakes students make with biochemistry? How can biochemistry help taxonomists? What biochemical molecules contain pyrimidine rings? What biochemical molecules make up enzymes? See all questions in Biochemical Molecules. Impact of this question views around the world. You can reuse this answer Creative Commons License. This resulting molecule is called a triglyceride.

Because carbon-hydrogen bonds are considered energy rich, fats store a lot of energy per unit. In fact, a gram of fat stores more than twice as much energy as a gram of a polysaccharide such as starch. Fats are lipids that are used by living organisms for stored energy. A saturated fatty acid has hydrogen atoms bonded to all available carbon atoms. An unsaturated fatty acid has one or more carbon atoms double-bonded to the neighboring carbon atom so that fewer hydrogen atoms are needed to create a stable electron cloud.

With fewer hydrogen atoms attached, the molecule is considered unsaturated with hydrogen atoms. So saturated fatty acids have more hydrogen atoms attached than unsaturated fatty acid chains. Through their metabolism, plants generally produce triglycerides that contain unsaturated fatty acids such as peanut oil or olive oil, whereas animals generally produce triglycerides that contain saturated fatty acids which humans sometimes convert into butter and lard.

Waxes are similar to fats except that waxes are composed of only one long-chain fatty acid bonded to a long-chain alcohol group attached.

Because of their long, nonpolar carbon chains, waxes are extremely hydrophobic meaning they lack an affinity for water. Both plants and animals use this waterproofing characteristic as part of their composition.

The chemical and physical properties of the different fatty acids, such as their solubility in non-polar solvents and the melting point, will depend on the number of carbon atoms of the molecule. The higher the number of carbon atoms of the chain the higher will be melting point of the fatty acid. According to the chain length fatty acids are referred as short-chain fatty acids, those having four C4 to ten C10 carbons; as medium-chain fatty acids those having twelve C12 to fourteen C14 carbons; long-chain fatty acids to those of sixteen C16 to eighteen carbons C18 ; and very long-chain fatty acids those having twenty C20 or more carbon atoms.

Molecules having less than four carbon atoms C2; acetic acid and C3; propionic acid are not considered fatty acids due their high water solubility. On the other side, fatty acids of high number of carbon atoms are not frequent, however are present in significant amount in the brain of vertebrates, including mammals and human. In the human brain have been identified fatty acids as long as 36 carbon atoms [ 20 ]. The link between carbons in fatty acids, correspond to a covalent bond which may be single saturated bond or double unsaturated bond.

The number of unsaturated bonds in the same molecules can range from one to six double bonds. Thus, the more simple classification of the fatty acids, divided them in those that have not double bonds, named saturated fatty acids SAFA , and fatty acids that have one or more double bonds, collectively named unsaturated fatty acids. In turn, when the molecule has one unsaturation it is classified as monounsaturated fatty acid MUFA and when has two to six unsaturations are classified as polyunsaturated fatty acids PUFAs [ 21 ].

The presence of unsaturation or double bonds in fatty acids is represented by denoting the number of carbons of the molecule followed by an indication of the number of double bonds, thus: C corresponds to a fatty acid of 18 carbons and one unsaturation, it will be a MUFA. C 4 correspond to a molecule having 20 carbons and four double bonds, being a PUFA.

However, in the cell the metabolic utilization of fatty acids occurs by the successive scission of two carbon atoms from the C1 to the Cn mitochondrial or peroxisomal beta oxidation.

This means that as the fatty acid is being metabolized oxidized in beta position , the number of each carbon atom will change, creating a problem for the identification of the metabolic products formed as the oxidation progress.

For this reason R. Holman, in , proposed a new type of notation that is now widely used for the biochemical and nutritional identification of fatty acids [ 24 ]. This nomenclature lists the carbon enumeration from the other extreme of the fatty acid molecule.

The latter notation is the most often used in nutrition and refers to the last letter of the Greek alphabet [ 25 ]. What happens with fatty acids having more than a double bond? Double bonds are not randomly arranged in the fatty acid structure. Nature has been "ordained" as largely incorporate them in well-defined positions.

This particular structural disposition of double bonds, i. Oleic acid is highly abundant both in vegetable and animal tissues. ALA is a less abundant fatty acid, almost exclusively present in the vegetable kingdom and specifically in land-based plants [ 31 ]. The increase of double bonds in fatty acids significantly reduces its melting point. Thus, for a structure of the same number of carbon atoms, if it is saturated may give rise to a solid or semisolid product at room temperature, but if the same structure is unsaturated, may originate a liquid or less solid product at room temperature.

Different fatty acids, showing the C nomenclature, their systematic name, their common name and the respective melting point. The structural organization of fatty acids in food and in the body is mainly determined by the binding to glycerol by ester linkages.

The reaction of a hydroxyl group of glycerol, at any of its three groups, with a fatty acid gives rise to a monoacylglyceride. The linking of a second fatty acid, which may be similar or different from the existing fatty acid, gives rise to a diacylglyceride. If all three hydroxyl groups of glycerol are linked by fatty acids, then this will be a triacylglyceride [ 33 ].

Monoacylglycerides, by having free hydroxyl groups two are relatively polar and therefore partially soluble in water. Different monoacylglycerides linked to fatty acids of different lengths are used as emulsifiers in the food and pharmaceutical industry [ 34 ]. The less polar diacylglycerides which have only one free hydroxyl group are less polar than monoacylglycerides and less soluble in water. Finally, triacylglycerides, which lack of free hydroxyl groups are completely non-polar, but highly soluble in non-polar solvents, which are frequently used for their extraction from vegetable or animal tissues, because constitutes the energy reserve in these tissues [ 35 ].

Diacylglycerides and monoacylglycerides are important intermediates in the digestive and absorption process of fats and oils in animals. In turn, some of these molecules also perform other metabolic functions, such as diacylglycerides which may act as "second messengers" at the intracellular level and are also part of the composition of a new generation of oils nutritionally designed as "low calorie oils" [ 36 ].