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.
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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. Table 1. Geometrical isomers of fatty acids Carbon atoms forming the structure of the fatty acids possess a three-dimensional spatial structure which forms a perfect tetrahedron.
Positional isomers of fatty acids Positional isomerism refers to the different positions that can occupy one or more double bonds in the structure of a fatty acid. Table 2. More Print chapter. How to cite and reference Link to this chapter Copy to clipboard. Cite this chapter Copy to clipboard Rodrigo Valenzuela B. January 23rd Available from:. Over 21, IntechOpen readers like this topic Help us write another book on this subject and reach those readers Suggest a book topic Books open for submissions.
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Access personal reporting. More About Us. Systematic name. Common name. Saturated Fatty Acid. C 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.
Steroids, like cholesterol, play roles in reproduction, absorption, metabolism regulation, and brain activity. The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators. The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent.
Carnuba wax is valued for its toughness and water resistance. Phospholipids are the main constituents of cell membranes. They resemble the triglycerides in being ester or amide derivatives of glycerol or sphingosine with fatty acids and phosphoric acid.
The phosphate moiety of the resulting phosphatidic acid is further esterified with ethanolamine, choline or serine in the phospholipid itself. The following diagram shows the structures of some of these components.
Clicking on the diagram will change it to display structures for two representative phospholipids. To see a model of a phospholipid Click Here. As ionic amphiphiles, phospholipids aggregate or self-assemble when mixed with water, but in a different manner than the soaps and detergents. Because of the two pendant alkyl chains present in phospholipids and the unusual mixed charges in their head groups, micelle formation is unfavorable relative to a bilayer structure. If a phospholipid is smeared over a small hole in a thin piece of plastic immersed in water, a stable planar bilayer of phospholipid molecules is created at the hole.
As shown in the following diagram, the polar head groups on the faces of the bilayer contact water, and the hydrophobic alkyl chains form a nonpolar interior. The phospholipid molecules can move about in their half the bilayer, but there is a significant energy barrier preventing migration to the other side of the bilayer.
To see an enlarged segment of a phospholipid bilayer Click Here. This bilayer membrane structure is also found in aggregate structures called liposomes.
Liposomes are microscopic vesicles consisting of an aqueous core enclosed in one or more phospholipid layers. They are formed when phospholipids are vigorously mixed with water. Unlike micelles, liposomes have both aqueous interiors and exteriors. A cell may be considered a very complex liposome. The bilayer membrane that separates the interior of a cell from the surrounding fluids is largely composed of phospholipids, but it incorporates many other components, such as cholesterol, that contribute to its structural integrity.
Protein channels that permit the transport of various kinds of chemical species in and out of the cell are also important components of cell membranes. A very nice dynamic display of the gramicidin channel has been created by a collaboration of Canadian, French, Spanish and US scientists, and may be examined by Clicking Here.
The interior of a cell contains a variety of structures organelles that conduct chemical operations vital to the cells existence. Molecules bonded to the surfaces of cells serve to identify specific cells and facilitate interaction with external chemical entities. The sphingomyelins are also membrane lipids.
They are the major component of the myelin sheath surrounding nerve fibers. Multiple Sclerosis is a devastating disease in which the myelin sheath is lost, causing eventual paralysis.
The members of this group of structurally related natural hormones have an extraordinary range of biological effects. They can lower gastric secretions, stimulate uterine contractions, lower blood pressure, influence blood clotting and induce asthma-like allergic responses. Because their genesis in body tissues is tied to the metabolism of the essential fatty acid arachadonic acid 5,8,11,eicosatetraenoic acid they are classified as eicosanoids.
Many properties of the common drug aspirin result from its effect on the cascade of reactions associated with these hormones. The metabolic pathways by which arachidonic acid is converted to the various eicosanoids are complex and will not be discussed here. A rough outline of some of the transformations that take place is provided below.
It is helpful to view arachadonic acid in the coiled conformation shown in the shaded box. Leukotriene A is a precursor to other leukotriene derivatives by epoxide opening reactions. The prostaglandins are given systematic names that reflect their structure.
The initially formed peroxide PGH 2 is a common intermediate to other prostaglandins, as well as thromboxanes such as TXA 2. Compounds classified as terpenes constitute what is arguably the largest and most diverse class of natural products.
A majority of these compounds are found only in plants, but some of the larger and more complex terpenes e. Terpenes incorporating most of the common functional groups are known, so this does not provide a useful means of classification. Instead, the number and structural organization of carbons is a definitive characteristic. Terpenes may be considered to be made up of isoprene more accurately isopentane units, an empirical feature known as the isoprene rule.
Because of this, terpenes usually have 5n carbon atoms n is an integer , and are subdivided as follows:. Classification Isoprene Units. Isoprene itself, a C 5 H 8 gaseous hydrocarbon, is emitted by the leaves of various plants as a natural byproduct of plant metabolism.
Next to methane it is the most common volatile organic compound found in the atmosphere. Examples of C 10 and higher terpenes, representing the four most common classes are shown in the following diagram. The initial display is of monoterpenes; larger terpenes will be shown by clicking the " Toggle Structures " button under the diagram. Most terpenes may be structurally dissected into isopentane segments.
To see how this is done click directly on the structures in the diagram. The isopentane units in most of these terpenes are easy to discern, and are defined by the shaded areas. In the case of the monoterpene camphor, the units overlap to such a degree it is easier to distinguish them by coloring the carbon chains. This is also done for alpha-pinene. In the case of the triterpene lanosterol we see an interesting deviation from the isoprene rule.
This thirty carbon compound is clearly a terpene, and four of the six isopentane units can be identified. However, the ten carbons in center of the molecule cannot be dissected in this manner. Evidence exists that the two methyl groups circled in magenta and light blue have moved from their original isoprenoid locations marked by small circles of the same color to their present location.
This rearrangement is described in the biosynthesis section. Similar alkyl group rearrangements account for other terpenes that do not strictly follow the isoprene rule. To see a model of the monoterpene camphor Click Here. Polymeric isoprenoid hydrocarbons have also been identified. Rubber is undoubtedly the best known and most widely used compound of this kind. As a result, the end of the water molecule where oxygen is located is relatively negative in charge, whereas the end with hydrogens is relatively positively charged.
The positive ends of the water molecule are attracted to the negative ends of adjacent water molecules, as shown in the figure below, and this enables water molecules to coalesce. You may have also seen water bead on a car windshield as a result of this phenomenon.
Lipids, i. Non-polar molecules do not dissolve well in polar solutions like water; in fact, polar and non-polar molecules tend to repel each other in the same way that oil and water don't mix and will separate from each other even if they are shaken vigorously in an attempt to mix them. This distinction between polar and non-polar molecules has important consequences for living things, which are composed of both polar molecules and non-polar molecules.
The next sections will illustrate the importance of this. Fatty acids are chain-like molecules that are important components of several types of lipids. The illustrations below show two different fatty acid molecules. Each has a characteristic carboxyl group the -COOH attached to a chain of carbons with hydrogen atoms attached to the carbon chain.
Two things are noteworthy. First, the hydrocarbon chain is very non-polar and therefore doesn't dissolve in water very well. However, hydrocarbon chains do associate with each other readily.
Second, note that the unsaturated fatty acid has two hydrogens removed, and this allows formation of a double bond, i.
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