Physical And Chemical Properties Of Lipids Pdf
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Hamdy A. Tawfeuk 2.
Lipid , any of a diverse group of organic compounds including fats , oils , hormones , and certain components of membranes that are grouped together because they do not interact appreciably with water. One type of lipid, the triglycerides , is sequestered as fat in adipose cells , which serve as the energy-storage depot for organisms and also provide thermal insulation. Some lipids such as steroid hormones serve as chemical messengers between cells , tissues , and organs , and others communicate signals between biochemical systems within a single cell.
Physical Chemistry of Fats
Lipid , any of a diverse group of organic compounds including fats , oils , hormones , and certain components of membranes that are grouped together because they do not interact appreciably with water. One type of lipid, the triglycerides , is sequestered as fat in adipose cells , which serve as the energy-storage depot for organisms and also provide thermal insulation.
Some lipids such as steroid hormones serve as chemical messengers between cells , tissues , and organs , and others communicate signals between biochemical systems within a single cell.
The membranes of cells and organelles structures within cells are microscopically thin structures formed from two layers of phospholipid molecules. Membranes function to separate individual cells from their environments and to compartmentalize the cell interior into structures that carry out special functions. So important is this compartmentalizing function that membranes, and the lipids that form them, must have been essential to the origin of life itself.
A lipid is any of various organic compounds that are insoluble in water. Together with proteins and carbohydrates , lipids are one of the principal structural components of living cells. Lipids are a diverse group of compounds and serve many different functions. At a cellular level, phospholipids and cholesterol are some of the primary components of the membranes that separate a cell from its environment. Lipid-derived hormones, known as steroid hormones , are important chemical messengers and include testosterone and estrogens.
At an organismal level triglycerides stored in adipose cells serve as energy-storage depots and also provide thermal insulation. Lipid rafts are possible areas of the cell membrane that contain high concentrations of cholesterol and glycosphingolipids. The existence of lipid rafts has not been conclusively established, though many researchers suspect such rafts do indeed exist and may play a role in membrane fluidity, cell-to-cell communication, and infection by viruses.
Water is the biological milieu—the substance that makes life possible—and almost all the molecular components of living cells, whether they be found in animals, plants, or microorganisms, are soluble in water. Some lipids are amphipathic—part of their structure is hydrophilic and another part, usually a larger section, is hydrophobic. Amphipathic lipids exhibit a unique behaviour in water: they spontaneously form ordered molecular aggregates , with their hydrophilic ends on the outside, in contact with the water, and their hydrophobic parts on the inside, shielded from the water.
This property is key to their role as the fundamental components of cellular and organelle membranes. Although biological lipids are not large macromolecular polymers e. Many of these molecular building blocks are similar, or homologous, in structure. The homologies allow lipids to be classified into a few major groups: fatty acids, fatty acid derivatives, cholesterol and its derivatives, and lipoproteins.
This article covers the major groups and explains how these molecules function as energy-storage molecules, chemical messengers, and structural components of cells. Fatty acids rarely occur as free molecules in nature but are usually found as components of many complex lipid molecules such as fats energy-storage compounds and phospholipids the primary lipid components of cellular membranes.
This section describes the structure and physical and chemical properties of fatty acids. It also explains how living organisms obtain fatty acids, both from their diets and through metabolic breakdown of stored fats.
Biological fatty acids, members of the class of compounds known as carboxylic acids , are composed of a hydrocarbon chain with one terminal carboxyl group COOH. The fragment of a carboxylic acid not including the hydroxyl OH group is called an acyl group.
Most biological fatty acids contain an even number of carbon atoms because the biosynthetic pathway common to all organisms involves chemically linking two-carbon units together although relatively small amounts of odd-number fatty acids do occur in some organisms. Although the molecule as a whole is water-insoluble by virtue of its hydrophobic hydrocarbon chain, the negatively charged carboxylate is hydrophilic.
This common form for biological lipids—one that contains well-separated hydrophobic and hydrophilic parts—is called amphipathic.
In addition to straight-chain hydrocarbons, fatty acids may also contain pairs of carbons linked by one or more double bonds, methyl branches, or a three-carbon cyclopropane ring near the centre of the carbon chain.
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External Websites. Thomas E. See Article History. Structure and properties of two representative lipids. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.
Top Questions. A false colour transmission electron microscope micrograph of an oogonium an egg cell of certain algae and fungi , showing an abundance of lipid droplets yellow , a nucleus green , an atypical nucleolus dark blue , and mitochondria red. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Load Next Page.
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Analysis of Lipids. Lipids are one of the major constituents of foods, and are important in our diet for a number of reasons. They are a major source of energy and provide essential lipid nutrients. Nevertheless, over-consumption of certain lipid components can be detrimental to our health, e. In many foods the lipid component plays a major role in determining the overall physical characteristics, such as flavor, texture, mouthfeel and appearance. For this reason, it is difficult to develop low-fat alternatives of many foods, because once the fat is removed some of the most important physical characteristics are lost.
Once production of your article has started, you can track the status of your article via Track Your Accepted Article. Help expand a public dataset of research that support the SDGs. Chemistry and Physics of Lipids publishes research papers and review articles on chemical and physical aspects of lipids with primary emphasis on the relationship of these properties to biological functions and to biomedical applications. Accordingly, the journal covers: advances in synthetic and analytical lipid methodology; mass-spectrometry of lipids; chemical and physical characterisation of isolated structures; thermodynamics, phase behaviour, topology and dynamics of lipid assemblies; physicochemical studies into lipid-lipid and lipid-protein interactions in lipoproteins and in natural and model membranes; movement of lipids within, across and between membranes; intracellular lipid transfer; structure-function relationships and the nature of lipid-derived second messengers; chemical, physical and functional alterations of lipids induced by free radicals; enzymatic and non-enzymatic mechanisms of lipid peroxidation in cells, tissues, biofluids; oxidative lipidomics; and the role of lipids in the regulation of membrane-dependent biological processes. Reviews, full articles and short communications will be considered for publication in each issue. Special Issues will consist of invited contributions organized and edited to cover specific themes.
Fatty acid bioavailability can be managed through the physicochemical properties of lipid such as lipid-droplet size, lipid-droplet ultrastructure.
Chemistry and Physics of Lipids
Physical properties of structured lipids from lard and soybean oil produced by enzymatic interesterification. The main goal of the present research was to evaluate the physical properties of blends of lard and soybean oil modified by enzymatic interesterification catalyzed by two different commercial microbial lipases, viz. Pure lard exhibited a softening point of ca. This result was most likely due to the sn -1,3-specificity of M10 lipase. Pure lard displayed a lower SFC after interesterification, and M10 lipase proved to be more effective than AY30 lipase.
The analysis of the physical properties of oils and fats allows us to understand the behavior and characteristics of these elements, as well as their differences. For this, the crystallization, the melting point, the viscosity, the refractive index, the density, the solubility, the plasticity and the emulsifying capacity will be analyzed. Here we provide more detail on each of these. Fats differ from oils in their degree of solidification at room temperature, since in these conditions the oils are in a liquid state not crystallized while the fats are in the solid crystallized state. The proportion of crystals in fats have great importance in determining the physical properties of a product.
Most people think "lipid" is just another term for "fat," but lipids are actually an entire class of molecules. By definition, lipids include any compound created by living organisms that resists reaction with water, including fats, hormones, oils and membranes. Lipids serve many important roles, including energy storage, insulation, carrying messages between cells and forming cellular membranes.
Dilini N. Perera, Geeth G.
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