Biological lipids are a chemically diverse group of compounds, the common and defining feature of which is their insolubility in water. The biological functions of the lipids are as diverse as their chemistry. Fats and oils are the principal stored forms of energy in many organisms. Phospholipids and sterols are major structural elements of biological membranes. Other lipids, although present in relatively small quantities, play crucial roles as enzyme cofactors, electron carriers, light-absorbing pigments, hydrophobic anchors for proteins, “chaperones” to help membrane proteins fold, and emulsifying agents in the digestive tract, hormones, and intracellular messengers. This chapter introduces representative lipids of each type, with emphasis on their chemical structure and physical properties. (Nelson & Cox, 2008)
According To Campbell, 2009, Biochemistry 6th Edition, lipids are compounds that occur frequently in nature. They are found in places as diverse as egg yolks and the human nervous system and are an important component of plant, animal, and microbial membranes. The defi nition of a lipid is based on solubility. Lipids are marginally soluble (at best) in water but readily soluble in organic solvents, such as chloroform or acetone. Fats and oils are typical lipids in terms of their solubility, but that fact does not really define their chemical nature. In terms of chemistry, lipids are a mixed bag of compounds that share some properties based on structural similarities, mainly a preponderance of nonpolar groups. Classified according to their chemical nature, lipids fall into two main groups. One group, which consists of open-chain compounds with polar head groups and long nonpolar tails, includes fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, and glycolipids. The second major group consists of fusedring compounds, the steroids; an important representative of this group is cholesterol.
The following statements are the objectives of this experiment: to investigate the lipid composition of common foods such as corn oil and egg yolk, and glycerol. The significance of this experiment to verify lipids if they are present or absent in such known foods that contained lipids through different tests. And also for the students to understand deeply through personal experience and could conclude whether it is positively or negatively present according to the corresponding results. The scope of this experiment involves qualitative analysis helps to reveal the ability of the student to verify and understand those reactions could be obtained in the experiment. This is limited in the availability of the reagents to be used in each test, the samples to be tested and the substitution of chemicals restricted to use in the experiment that student could be able to verify experimentally. Since, there are some of them which are not available in the laboratory and failed to substitute chemicals.
Lipids are chemically heterogeneous mixtures. The only common property they have is their insolubility in water. We can test for the presence of various lipids by analyzing their chemical constituents. Foods contain a variety of lipids; most important among them are fats, complex lipids, and steroids. Fats are triglycerides, esters of fatty acids and glycerol. Complex lipids also contain fatty acids, but their alcohol may be either glycerol or sphingosine. They also contain other constituents such as phosphate, choline, ethanolamine, or mono– to oligosaccharides. An important representative of this group is lecithin, a glycerophospholipid, containing fatty acids, glycerol, phosphate, and choline. The most important steroid in food is cholesterol. Different foods contain different proportions of these three groups of lipids. Structurally, cholesterol contains the steroid nucleus that is the common core of all steroids:
A test that differentiates between cholesterol and...
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