What is lipids? Lipids are a broad group of naturally occurring molecules which includes fats , waxes , sterols , fat-soluble vitamins , monoglycerides , diglycerides , phospholipids , and others.
Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides. Lipids also encompass molecules such as fatty acids and their derivatives (including tri-,di-, and monoglycerides and phospholipids), as well as other stero-containing metabolites such as cholesterol.
It is a second group of organic compounds that serve as food for the body.
It is soluble in water. It is soluble in nonpolar organic solvents such as ether, acetone, CCl4. It contains C, H, O, sometimes N or K It yields fatty acids on hydrolysis.
It combines with fatty acids to form esters . It takes part in plant and animal metabolism.
FATTY ACIDS -are straight chain organic acids. -usually contain even number of carbon atoms -can be saturated (contain one bond) or unsaturated ( contain one or more double bonds)
“ The greater the degree of unsaturation, the lower the melting point ” Unsaturated fatty acids have lower melting points than the saturated fatty acids.
The 18-carbon fatty acid, stearic acid, melts at 70°C. C17H35COOH
18-carbon fatty acid with one double bond, oleic acid, melts at 13°C. C17H33COOH
18-carbon fatty acid with two double bonds, linoleic acid, melts at -5°C. C17H31COOH
18-carbon fatty acid with three double bonds, linolenic acid, melts at -10°C. C17H29COOH
Unsaturated Fatty Acids can be subdivided into the ff: - Monounsaturated , those contain only one double bond - Polyunsaturated , those that contain many double bonds - Eicosanoids , which include the porstaglandins, leikotrienes, prostacyclins, and thromboxanes
Linoleic acid is the essential fatty acid – it is essential for the complete nutrition of the human body.It cannot be synthesized in the body and must be supplied from food we eat.
Arachidonic and linolenic acid, which were formerly also designated as essential fatty acids, ca be synthesized by the body from linoleic acid. Linoleic acid is be found in the large concentrations of corn, cottonseed, peanut and soybean oils but not in coconut oil and olive oils. One of the functions of this fatty acid is synthesis of prostaglandins.
The absence of the essential fatty acid from the diet of an infant causes loss of weight and also “eczema”. These conditions can be cured by administering corn oil or linseed oil.
Dietary saturated fat increase the blood levels of LDL – low density lipoprotein , which aid in the desposition of cholesterol on the artery walls.
Partially hydrogenated vegetable oils have been substituted for saturated fats as a way to lower both cholesterol and LDL levels in the blood. But those effect were opposite to that which was desired.
Natural vegetable oils contain primarily cis isomers but partially hydrogenated produces a mixture of cis and trans isomers. It is the trans isomers that cause many undesirable effects such as lowering of HDL (the good cholesterol) levels, raising the LDL (bad cholesterol) levels and raising total cholesterol levels.
CLASSIFICATION of Lipids 1)Simple Lipids -are esters of fatty acids. The hydrolysis of a simple lipid may be expressed as Simple lipid + H2O hydrolysis fatty acids + alcohol
If the hydrolysis of a simple lipid yields three fatty acids and glycerol, the simple lipid is called a fat or an oil. If the Hydrolysis of a simple lipid yields a fatty acid and high molecular mass monohydric alcohol, the simple lipid is wax .
Complex Lipids -on hydrolysis yield one or more fatty acids, an alcohol, and some other type of compound. In this category are phospholipids and glycolipids .
Precursor and derived Lipids -are compounds produced when simple and complex lipids undergo hydrolysis. They include such substances as fatty acids, glycerol, sphingosine, and other alcohols.
Derived Lipids are formed by metabolic transformation of fatty acids. They include ketone bodies, steroids, fatty aldehydes, prostaglandins, and lipid-soluble vitamins.
FATS and OILS Fats are esters formed by the combination of a fatty acid with one particular alcohol glycerol. If one molecule of glycerol reacts with one molecule of stearic acid, (a fatty acid), glyceryl monostearate is formed.
The glycerol molecule contains three – OH groups and so combines with three fatty acid molecules. However, these fatty acids molecules do not have to be the same. Fats and oils can contain three different fatty acid molecules, which can be saturated, unsaturated or some combination of these.
An example of a mixed triglyceride formed from the reaction of glycerol with three different fatty acid molecules as follows. The fatty acids are oleic, stearic, and linoleic.