Lipids

LIPIDS• Lipids are a large and diverse group of naturally occurring organic

compounds that are related by their solubility in nonpolar organic

solvents and general insolubility in water.

• They are formed by condensation reaction between fatty acids and

alcohols.

• Lipids are esters of moderate to long chain fatty acids with alcohols

• The main biological functions of lipids include energy storage, as

structural components of cell membranes, and as important signalling

molecules.• Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents

such as chloroform, methanol.

FATTY ACIDS

• The lipid building blocks.

• Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.

• The fatty acid chains are usually between 10 and 20 Carbon atoms long.

• The fatty "tail" is non-polar (Hydrophobic) while the Carboxyl "head" is a little polar (Hydrophillic).

• Eg: A 16-C fatty acid: CH3(CH2)14-COO-

Non-polar polar

Fatty Acids

• The carbon chain of fatty acids may be saturated or

unsaturated.

• Where a double bond exists, there is the possibility of

either a cis or a trans geometric isomerism.

• Most naturally occurring fatty acids are of the cis

configuration.

Cis and trans-2-butene

Fatty acids

• Fatty acids are of two types:• Saturated : only single bonds between Carbon

atoms• Unsaturated : contain one or more double

bonds.• The double bond gives unsaturated fatty acids

a bend in the chain. This bend affects the chemical characteristics of unsaturated fatty acids.

Saturated FattyAcids

• Contain only single C–C bonds

• Closely packed • Strong attractions between

chains• High melting points• Solids at room temperature• Eg: Butter,

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Unsaturated Fatty Acids

• Contain one or more double C=C bonds

• Nonlinear chains do not allow molecules to pack closely

• Few interactions between chains

• Low melting points• Liquids at room

temperature• Eg: Vegetable oils

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Some fatty acids and their common names:14:0 myristic acid16:0 palmitic acid 18:0 stearic acid18:1 cis9 oleic acid18:2 cis9,12 linoleic acid18:3 cis9,12,15 -linolenic acid 20:4 cis5,8,11,14 arachidonic acid

Most naturally occurring fatty acids have an even number of carbon atoms.

Examples of Fatty Acids

Naming a Fatty Acid:First digit: No of Carbon atomsSecond Digit: No of double bondsPosition of Double bond

Classification of Lipids

• Based on their functions lipids are classified as

• Storage Lipids: Triglycerides • Membrane Lipids: Phospholipids, Glycolipids

Storage Lipids: Triglycerides

• The triesters of fatty acids with glycerol compose the class of lipids known as fats and oils.

• These triglycerides are found in both plants and animals.- they are the simplest lipids

• Triglycerides that are solid or semisolid at room temperature are classified as fats, and occur predominantly in animals.

• Those triglycerides that are liquid are called oils and originate chiefly in plants.

Storage Lipids: Triglycerides

• Triglycerides are Energy-storage molecules. They are formed by connecting three fatty acids to a molecule Glycerol.

Storage Lipids :Waxes• Biological waxes are esters of long-chain (C14 to

C36) saturated and unsaturated fatty acids with long-chain (C16 to C30) alcohols.

• In addition to being storage form of metabolic fuel, waxes have other diverse roles: as water-repellent, coating on leave surface to prevent excess evaporation

Membrane Lipids: Phospholipids

• This class of lipids are really derivatives of triglycerides.

• They are composed of a glycerol molecule with two fatty acids (a diglyceride).

• The third carbon contains a phosphate group and usually some added polar molecule (such as ethanolamine, serine or choline)

Membrane Lipids :Phospholipids

• Major component of

all cell membranes as

they can form lipid

bilayers.

Membrane Lipids:Glycolipids

• Glycolipids are composed of lipids that are covalently bonded to monosaccharides or polysaccharides.

• Their role is to provide energy and also serve as markers for cellular recognition.

Sphingolipids

• Are a class of lipids which are composed of one molecule of long chain alcohol called sphingosine.

• Instead of glycerol these lipids have Sphingosine.

• These compounds play important roles in signal transmission and cell recognition

Membrane Lipids: Cholesterol

C holestero lHO

Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail. Cholesterol is largely hydrophobic.

But it has one polar group, a hydroxyl, making it amphipathic.

SUMMARY