Lipids classification structure and biological role LIPIDS Lipids

Lipids classification, structure and biological role.

LIPIDS Lipids are a class of biological molecules defined by low solubility in water and high solubility in nonpolar solvents. As molecules that are largely hydrocarbon in nature, lipids represent highly reduced forms of carbon and, upon oxidation in metabolism, yield large amounts of energy. Lipids are thus the molecules of choice for metabolic energy storage.

Biological functions • Energy production and storage: The most important role of lipids is as а fuel. Thus fat is the most concentrated form in which potential energy can be stored. • Insulation and protection: Since fat is а bad conductor of heat, it provides excellent insulation. Fat may also provide padding to protect the internal organs. • Structural function: They provide structure and support for the walls of every cell in your body.

Biological functions • Hormone production: Cholesterol is a type of lipid needed to produce important steroid hormones in the body. • Chemical messengers: Some lipids such as steroid hormones serve as chemical messengers (primary messengers) between cells, tissues and organs.

Classification On the basis of whether they undergo hydrolysis reactions in alkaline solution: 1. Saponifiable lipids can be hydrolyzed under alkaline conditions to yield salts of fatty acids. 2. Nonsaponifiable lipids do not undergo hydrolysis reactions in alkaline solution. A saponifiable lipid is a compound that undergoes saponification reaction into yield smaller product molecules.

Classification • A saponification reaction is an organic chemical reaction that utilizes an alkali to cleave an ester into a carboxylic acid salt and alcohol. • The primary use for this reaction is during the production of soap products. • Potassium hydroxide (KOH) and sodium hydroxide (Na. OH) are the two most common alkalis used with saponification to produce soap products.

Classification By structure: 1. Simple: fats, oils, waxes, steroids. 2. Complex: phospholipids, sphingolipids, glycolipids. 3. Derived lipids: hormones, fat-solubility vitamins

Fatty acids • Fatty acids are saponifiable lipid building blocks. • Fatty acids are naturally occurring carboxylic acids with an unbranched carbon chain. • Usually straight-chain having even number (4 -28) of carbon atoms • Long-chain fatty acids (12 to 28 carbon atoms) are found in meats and fish; medium-chain fatty acids (6 to 10 carbon atoms) and short-chain fatty acids (fewer than 6 carbon atoms) occur primarily in dairy products. • Fatty acids are classified into saturated and unsaturated.

Saturated fatty acid • Fatty acid chains that contain only carbon-carbon single bonds are referred to as saturated. • Palmitic acid:

Unsaturated fatty acid • Those molecules that contain one or more double bonds are called unsaturated. Oleic acid:

Structure of fatty acids

saturated Fatty Acids Fatty Acid # of Carbons # of C=C lauric 12 0 myristic 14 0 palmitic 16 0 stearic 18 0

Unsaturated Fatty Acids Fatty Acid # of Carbons # of C=C oleic 18 1 linoleic 18 2 linolenic 18 3 arachidonic 20 4