Lipids are a class of heterogenous compounds which are relatively insoluble in water and soluble in nonpolar solvents. Chemically: either esters of fatty acids or substances capable of forming such esters
BIOMEDICAL IMPORTANCE1. Stored as a source of energy in the body. Lipid (TGL) Droplets In Adipose tissue
3. Thermal Insulator : Provides insulation against changes in external temperature.
4. Lipids act as electric insulators in neurons.
5. Act as metabolic regulators (steroid hormones and prostaglandins).6. Act as surfactants and prevents collapse of lungs during expiration.7. Lipids are used as detergents.8. Lipids used in emulsification and intestinal absorption of non polar nutrients like fatty acids and fat soluble vitamins.9. Associated with diseases such as atherosclerosis, diabetes mellitus and obesity.10. Gives shape and contour to the body.
1. Simple LipidsEsters of fatty acids with various alcohols. a. Fats :esters of fatty acids with glycerol. eg: triglycerides. b. Waxes: esters of fatty acids with higher molecular weight monohydric alcohols. eg: beeswax Glycerol
2. Compound LipidsEsters of fatty acids with various alcohols alongwith an additional group. Simple lipid + Additional group = Compound Lipids a. Phospholipids: b. Glycolipids: c. Other Complex Lipids:
COMPOUND LIPIDSEsters of fatty acids with various alcohols alongWith an additional group. Phospholipids Glycolipids OthersGlycerphospholipids -Phosphatidyl choline Cerebrosides Lipoproteins - Phosphatidyl ethanolamine Gangliosides Aminolipids - Phosphatidyl serine - Phosphatidyl inositol Globosides - Cardiolipin - PlasmalogensSphingophospholipids
3. Derived LipidsLipid molecules derived from simple/compound lipidson their hydrolysis Fatty acids Eicosanoides Steroids Sterols Cholesterol Bile acids Vitamins (A,D,E,K) Ketone Bodies
CLASSIFICATION OF FATTY ACIDSBased on ‘R’ group 1. Small / Medium / Long Chain Fatty Acids 2. Odd / Even Chain Fatty Acids 3. Saturated / Unsaturated Fatty AcidsNutritionally Essential / Non-Essential Fatty Acids
1. Small / Medium / Long Chain Fatty AcidsSmall chain Fatty acids : 2 – 4 carbons Medium chain Fatty acids : 6 – 14 carbons Long chain Fatty acids : more than 16 carbons
USES / FUNCTIONS OF PUFA Major components of membrane lipids Contributes to the fluidity of membranes Used for Prostaglandin synthesis Decreases the incidence of Atherosclerosis,Coronary Artery Diseases
Saturated fatty acids: rich in storage lipids (adipose tissue)Unsaturated fatty acids: rich in membrane lipids(to increase fluidity)
Essential Fatty AcidsFatty acids that can not be synthesized by body & has tobe supplied by dietEx: Linoleic acid Linolenic acid Arachidonic acidFunctions: Structural composition of Brain & Nervous system Precursor for Eicosanoid synthesis Prevents atherosclerosis Prevents skin lesions
12 11 10 9 8 7 6 5 4 3 2 1ω ε δ γ β α Two types 1. ω – type 2. N - type
Indicating Number & Position of Double Bond 18:1,9 Δ9 18:1 ω3, ω6, ω9 Fatty Acids ω9,C18:1
Melting Point :• Temperature at which fats are converted from solid state to liquid state.• Saturated acids have high melting point than unsaturated acids• Increases with increase in hydrocarbon chain lengthSolubility: Decreases with increasing chain length Increases with temperature.Unsaturated fatty acids exhibit cis-trans isomerism
GEOMETRIC ISOMERISM OF OLEIC AND ELAIDIC ACIDS Natural Fatty acids – ‘cis’ form
1. Salt Formation2. Esterification3. Hydrogenation4. Halogenation5. Hydrolysis6. Oxidation
1. SALT FORMATIONR – COOH + NaCl R – COONa + HClFatty acids react with alkalies to form Salts of fatty acidsNa+ or K+ salts of fatty acids : Soaps
2. ESTERIFICATION + +Most of the fatty acids of body are in esterified form
3. HYDROGENATION (hardening) CH3 – CH2 – CH – CH – CH2 – COOH – H2 CH3 – CH2 – CH2 – CH2 – CH2 – COOHUnsaturated FA converted to Saturated FAUsed to synthesize Vanaspathi & MargaraineTrans Fatty acids are formed
4. HALOGENATION CH3 – CH2 – CH – CH – CH2 – COOH – I2 CH3 – CH2 – CH – CH – CH2 – COOH I IThe amount of halogen taken by a fatty acid depends on No of double bonds Degree of unsaturation
TAG undergoes stepwise hydrolysis of its ester bonds toform Glycerol & Free Fatty acids LipasesDigestion of Fats in GITMobilisation of TGL from Adipose tissue
1. Structural components of cell membrane.2. Enable enzyme action.(mitochondrial enzyme system).3. Required for blood coagulation (prothrombin to thrombin, activation of factor 8 by factor 9).4. Transports lipids from intestine and liver.5. Choline acts as a lipotropic agent since it prevents the formation of fatty liver.6. Phospholipids of myelin sheath provides insulation around nerve fibers.
COMPOUND LIPIDSEsters of fatty acids with various alcohols alongWith an additional group. Phospholipids Glycolipids OthersGlycerphospholipids Cerebrosides AminolipidsSphingophospholipids Gangliosides Lipoproteins Sulfatides Globosides
o Lipids containing carbohydrate moiety - Glycolipidso Alcoholic component – Sphingosineo Ceramide – Common group of all Glycolipidso Occur in brain, spinal cords and other tissues.o Predominant in outer leaflet of biomembranes
GANGLIOSIDES (Ceramide + Oligosaccharide + Sialic acid) GM1 = Ganglioside with monosialic acid GD2 = Ganglioside with two sialic acid residues GT3 = Ganglioside with three sialic acid residuesSialic acid = N-Acetyl Neuraminic acid (NANA)
CHOLESTEROLChemistry: Has Steroid Nucleus OH group at 3rd position Double bond between 5th & 6th carbons 8-Carbon containing side chain at 17th position. 17 3 5 6
CHOLESTEROLChemical Properties 1. Undergoes rapid oxidation to form cholestenones. 2. Hydroxyl group forms esters with acids to form Cholesterol Esters (cholesterol acetate,palmitate and propionates) 3. Presence of double bond gives hydrogenation reactions (similar to unsaturated fatty acids). 4. Colour reactions: LIEBERMANN BURCHARD, SALKOWSKY, ZAKS.
CHOLESTEROLBiomedical ImportanceStructural role – Biomembranes, LipoproteinsOccur in large amounts in brain and nerve tissues.Act as insulator against nerve impulses which discharge electric charges.Biomolecules synthesized from cholesterol Bile acids Vitamin D Steroid hormones : Androgens, Estrogens, Progesterone, Aldosterone etc
BILE ACIDS Cholesterol is eliminated from the body as bile acids through bile. Help in digestion & absorption of fats and fat soluble vitamins Synthesised in liver, stored in gall bladder and act in intestine
BILE ACIDS Primary Bile Acids Secondary Bile AcidsSynthesised from Cholesterol Synthesised from primaryin Hepatocytes Bile acids in IntestineEx: Ex:Cholic acid Deoxycholic acidChenodeoxycholic acid Lithocholic acid
EICOSANOIDES20 CARBON CONTAINING FATTY ACIDS GENERATED FROMARACHIDONIC ACID • Discovered in prostate gland secretions • Synthesized in all tissues • Acts as local hormones • Function in even low concentrations
Prostaglandin O OHProtanoic acid – Precursor moleculeCyclopentane ring substituted with hydroxyl / keto groupsBased on difference in these substituted groups, PGs classified as PG-A, PG-B, PG-C, PG-D, PG-E, PG-F, PG-HBased on number of double bonds, PGs have three series PG1 – One double bond PG2 – 2 double bonds PG2 - most common series PG3 – 3 double bonds
Liposome FormationPrepared by sonication of amphipathic lipids
Liposomes Liposomes (microscopic spherical vesicles) when mixed with water under special condition, the phospholipids arrange themselves to form a bilayer membrane enclosing water-filled central core Impermeable to polar materials and helps maintain the composition of the enclosed aqueous fluid.
Uses of Liposomes To deliver drugs proteins enzymes genes
Lipoprotein Apo lipoprotein Functions (trnspt Chol.,)Chylomicron Apo AI, AI, B48, CI, CII, CIII, E Intestine to tissueVLDL B100, CI, CII, CIII, E Liver to tissueLDL B100 Liver to tissueIDL B100 Liver to tissueHDL Apo AI, AII, AIV, CI, CII, CIII, E Tissue to liver
RANCIDITY OF FATSFormation of unpleasant odour and taste in stored lipids iscalled as Rancidity.• Denotes the deterioration of lipids & becomes unsuitable for consumption• Occurs when exposed to air, moisture or bacteria• TGL with unsaturated fatty acids more susceptible for rancidity
Types of Rancidity1. Hydrolytic Rancidity: Partial hydrolysis of TGL by the bacterial enzymes 2. Oxidative Rancidity: Partial oxidation of fats leading to formation of peroxides & their corresponding aldehydes Prevented by adding Anti-oxidants
LIPID PEROXIDATION Free Radicals Lipids Lipid peroxides + Free Radicals O2Lipid peroxidation - generates of free radicals (ROO*,RO*,OH*)Free radicals : Have unpaired electrons in their outer orbits They oxidize & damage any biomoleculesPeroxidation : damages tissues in vivo,(free radicals) causes of cancer, Inflammatory diseases, atherosclerosis, and aging etc.
Three Stages of Peroxidation 1. Initiation2. Propagation3. Termination
Substances which control and prevent free radicals.Types1. Preventive Antioxidants: Decrease the rate of chain initiation step. Ex: Catalase, Metal ion chelators such as EDTA2. Chain Breaking Antioxidants: Interfere with chain propagation step. Ex : Superoxide dismutase(SOD), Vitamin EUses Protects biomembrane from the effect of free radicals Added in fats for storage purpose Protects the body from multiple diseases
Tests to check the purity of Simple Lipids1. Iodine Number2. Saponification Number3. Reichert Miesel Number4. Acid Number5. Acetyl number
Defined as the number of grams of iodine taken upby 100gms of fat.Index of degree of unsaturationIodine Number degree of unsaturation ﻌUses: To detect the degree of unsaturation To detect adulteration
SAPONIFICATION NUMBERDefined as the number of milligrams (mgs) of potassiumHydroxide (KOH) required to saponify one gram of fat.Index of molecular weight / chain length fatty acids 1Saponification Number ﻌ molecular weight (or) chain lengthUses: To detect molecular weight / chain length fatty acids To detect adulteration
ACETYL NUMBERDefined as the Milligrams of KOH required to combinewith the acetic acid liberated by the saponification of1 gm of acetylated fat. Indicator of number of hydroxyl groups Castor oil has acetyl value of 146 to 150 indicating the presence of sufficient hydroxylated acids. Butter has an acetyl value of 1.9 to 8.6 ,indicating the presence of very small amounts of hydroxylated acids.
REICHERT-MEISSL NUMBERDefined as the millimeters of 0.1N alkali required toneutralize the volatile acids obtained from 5 gm of fat . Butter fat has a Reichert-Meissl number of 26-33 whereas the number for lard is 0.6.
ACID NUMBERDefined as the Milligrams of KOH required to neutralizethe free fatty acids present in 1gm of fat. It is of value in determining rancidity due to free fatty acids.