Fatty Acids Fatty acids are aliphatic straight chain hydrocarbon compounds with a terminal carboxylic group. They are building blocks of lipids Insoluble in water Typically 12-18 carbon atoms (even number) Some contain double bonds Methyl group O C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3 HO Carboxyl group Hydrocarbon chain

C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3 O HO A typical fatty acid has a carboxyl group and hydrocarbon tail fatty acids with 16 and 18 carbon atoms are abundant in nature there are about 200 fatty acids Acetic acid (CH3COOH); Palmitic acid (C15H31COOH); Stearic acid (C17H35COOH); Oleic acid (C17H33COOH) they may or may not contain double bonds – fatty acids with double bonds are called as unsaturated fatty acids and fatty acids with double bonds are called as saturated fatty acids

Oleic acid with a single double bond C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3 O HO 1 2 3 4 5 6 7 8 9 10 The carbon atoms are numbered In most of the unsaturated fatty acids double bond lies between carbon atom 9 & 10. this designated as ∆9 C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH= CH – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3 O HO Oleic acid with a single double bond

When there are more than one double bond, the additional bond occurs between the ∆9 and the methyl terminal group The symbol 18:0 denotes a C18 fatty acid with no double bonds. The symbol 18:2 denotes a C18 fatty acid with two double bonds. similarly the symbol 18:2; 9, 12 is used to denote C18 fatty acid with two double bonds in the 9th and 12th position.

Triglycerides (Simple lipids) A simple lipid is formed when three molecules of fatty acids combine with one molecule of glycerol. In this process 3 molecules of water are released

Formation of a triglyceride, as simple lipid Tripalmitin Three molecules of palmitic acids combine with one molecule of glycerol. CH2OH CH2-O-COC15H31 - Palmitic acid Palmitic acid Palmitic acid - Palmitic acid CH2-O-COC15H31 Palmitic acid - Palmitic acid CH2-O-COC15H31 Formation of a triglyceride, as simple lipid

Formation of a triglyceride, as simple lipid Tristearin Three molecules of stearic acids combine with one molecule of glycerol. CH2OH CH2-O-COC17H35 - Stearic acid Stearic acid Stearic acid - Stearic acid CH2-O-COC17H35 Stearic acid - Stearic acid CH2-O-COC17H35 Formation of a triglyceride, as simple lipid

Formation of a triglyceride, as simple lipid Triolein Three molecules of oleic acids combine with one molecule of glycerol. CH2OH CH2-O-COC17H33 - Oleic acid Oleic acid Oleic acid - Oleic acid CH2-O-COC17H33 Oleic acid - Oleic acid CH2-O-COC17H33 Formation of a triglyceride, as simple lipid

Simple lipids When the three fatty acids of a lipid are similar, the fat is called a neutral fat When the three fatty acids of a lipid are different, the fat is called a mixed fat. Eg: dipalmito stearin

Mono & Diglycerides When only one fatty acid is combined to a glycerol, the fat is called as monoglyceride When two fatty acid are combined to a glycerol, the fat is called as diglyceride CH2OH CH2-O-COC15H31 - Palmitic acid CH2OH - Palmitic acid CH2-O-COC15H31 - Palmitic acid CH2-O-COC15H31 CHOH CH2OH CH2OH

Lipids on hydrolysis yields glycerol and fatty acids Simple lipids Compound lipids Derived lipids Compound lipids: contain some chemical groups in addition to fatty acids and glycerol. Eg: Lipid + Phosphate group : Phospholipids Lipid + Carbohydrate : Glycolipid Derived lipids: these are the hydrolyzed products of simple and compound lipids. Eg: Steroids, Terpenes, Carotenoids

Characteristics Fatty acids are building blocks of lipids They have a single carboxyl group and a long non-polar hydrocarbon tail (oily or greasy nature) carbon atoms are numbered starting at carboxyl terminus carbon atom 2 & 3 are often referred to as α and β respectively. The methyl carbon at the last is called ω carbon. C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3 O HO 1 2 3 4 5 6 7 8 9 10 α β ω

Fatty acids containing a single bond is called saturated fatty acid Fatty acids containing a single bond is called saturated fatty acid. The suffix – anoic indicates a saturated fatty acid Fatty acids containing one or more double bonds is called unsaturated fatty acid. The suffix – enoic indicates a saturated fatty acid Eg: Octadecanoic acid, Octadecenoic acid

PHOSPHOLIPIDS

Phospholipids are compound lipids Phospholipids are compound lipids. They are formed by glycerol, phosphoric acid and fattyacids. They are also called as phosphatids. They are the structural components of membranes and so are abundant in brain, kidney,etc.. Due to the presence of phosphoric acid group, phospholipids behave as polar lipids. They are hydrophilic in nature. Phospholipids are amphipathic.

TYPES OF PHOSPHOLIPIDS Phospholipids are further classified into: 1. lecithins. 2. cephalins. 3. plasmologens. 4. phosphoinositides. 5. phosphingosides.

Lecithins are the esters of glycerol with fattyacids. Two hydroxyl groups of glycerol are esterified by two fatty acid molecules. The third hydroxyl group of glycerol is esterified by a phosphoric acid molecule. The phosphoric acid group forms an ester with choline (nitrogenous base). CH2OH - Fatty acid - Fatty acid - Phosphoric acid - Choline

These are yellowish grey solids, soluble in ether, alcohol. found in all animals (brain, nerve tissue, sperm and egg yolk) and plants (seeds & sprouts). Lysolecithin injected into blood stream by snake bite causes rapid rapture of red blood cells. This is called hemolysis

These are more acidic than lecithins. CEPHALINS Cephalins are compound lipids. They are otherwise called phosphatidyl ethanolamine. These are more acidic than lecithins. They resemble lecithins except that the choline is replaced by ethanolamine or serine They consists of 4 components namely, glycerol, fatty acids, phosphatidyl ethanolamine. CH2OH - Fatty acid - Fatty acid - Phosphoric acid - Ethanolamine

PLASMOLOGENS :- These resemble lecithins and cephalins except in having one unsaturated ethen group in the place of fatty acid group. PHOSPHOINOSITIDES :- On hydrolysis it yields 1 glycerol, 2 molecules of fatty acids, 1 molecule of inositol (replaces the base) and 1/2/3 molecules of phosphoric acids PHOSPHINGOSIDES :- In these lipids glycerol is replaced by either sphingonise or a closely related dihydrosphingosine which are also nitrogenous bases. It is commonly found in nerve tissue.

GLYCOLIPIDS Glycolipids are compound lipids containing sugars and high molecular weight fatty acids like sphingosine and no phosphoric acid. It is found in brain, adrenals, kidney, spleen, liver, leucocytes, thymus, lungs, retina, egg-yolk and fish sperm. Gangliosides is a glycolipid found in brain tissue. These are found in ganglion cells of nervous tissue and also in parenchymatous tissue like spleen and erythrocytes.

It contains ceramide, N-acetyl neuraminic acid (NANA), N- acetyl galactosamine, carbohydrates (hexoses). Gangliosides are stored in large amounts in the brain and spleen. Glycolipids containing sulphur are called sulfolipids and sulfadites. These are widely distributed in plants. It is localised in chloroplasts. It is also found in the chromatophores of photosynthetic bacteria. It is present in the white matter of brain.

SPHINGOLIPIDS Sphingolipids, or glycosylceramides, are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extracts in the 1870s and were named for the mythological Sphinx because of their enigmatic nature.  These compounds play important roles in signal transmission and cell recognition.  Sphingolipidoses, or disorders of sphingolipid metabolism, have particular impact on neural tissue. A sphingolipid with an R group consisting of a hydrogen atom only is a ceramide. Other common R groups include phosphocholine, yielding a sphingomyelin, and various sugar monomers or dimers, yielding cerebrosides andglobosides, respectively. Cerebrosides and globosides are collectively known asglycosphingolipids.

STRUCTURE The long-chain bases, sometimes simply known as sphingoid bases, are the first non-transient products of de novo sphingolipid synthesis in both yeast and mammals. Ceramides and glycosphingolipids are N-acyl derivatives of these compounds.[4] The sphingosine backbone is O-linked to a charged head group such as ethanolamine, serine, or choline. The backbone is also amide-linked to an acyl group, such as a fatty acid.

TYPES Simple sphingolipids, which include the sphingoid bases and ceramides, make up the early products of the sphingolipid synthetic pathways. Sphingoid bases are the fundamental building blocks of all sphingolipids. The main mammalian sphingoid bases are dihydrosphingosine and sphingosine, while dihydrosphingosine and phytosphingosine are the principle sphingoid bases in yeast.[5][6] Sphingosine, dihydrosphingosine, and phytosphingosine may be phosphorylated.

Ceramides, as a general class, are N-acylated sphingoid bases lacking additional head groups. Dihydroceramide is produced by N-acylation of dihydrosphingosine. Dihydroceramide is found in both yeast and mammalian systems. Ceramide is produced in mammalian systems by desaturation of dihydroceramide by dihydroceramide desaturase 1 (DES1). This highly bioactive molecule may also be phosphorylated to form ceramide-1-phosphate. Phytoceramide is produced in yeast by hydroxylation of dihydroceramide at C-4.

STEROIDS Steroids are nonsaponifiable lipids. They cannot yield soap on hydrolysis because they do not contain fatty acids. Compounds containing 1,2-cyclopentanoperhydrophenanthrene nucleus in their structures are called steriods. Steroids are derived lipids. The steroids separate from fat, when fat is saponified. Steriods are readily soluble in ether, benzene, chloroform, petroleum ether and acetone but insoluble in water, acids and alkalies.

In the presence of bile salts, they are rendered soluble even in water. STRUCTURE :- Steroid contains four rings. They are named as A, B, C and D. The rings A, B and C are hexagons called cyclohexane rings and the ring D is a pentagon called cyclopentane. The 3 cyclohexane rings are fused in a non-linear or phenanthrene manner. The cyclopentane ring is fused terminally. This ring system is called cyclopentanophenanthrene or sterane.

The numbering of carbon atoms starts from rings A to D. Cholestrol, a steroid contains two angular methyl groups, namely C-18 and C- 19. Methyl group C-18 is attached to carbon atom number 13. Methyl group C-19 is attached to carbon atom number 10. A line above C-10 or C-13 denotes a methyl group. The steroids may have one or more alcoholic groups. The steroids containing alcoholic groups are called sterols. These are crystalline compounds containing secondary alcoholic group.

The common steroids are cholestrol, coprostanol, ergosterol, bile acids, androgens, oestrogens, progesterone, adrenal corticoids...

Types Sterols are found in plant and animal oils. Sterols are classified into 3groups based on their source of origin. They are: 1.ZOOSTEROLS :zoosterols are found in animals. eg :- Cholesterol 2.PHYTOSTEROLS : phytosterols are found in plants. eg :- Stigma sterols. 3.MYCOSTEROLS : mycosterols are commonly found in yeast and fungi. eg :- Ergosterol.