introduction to lipids
DESCRIPTION
Introduction to Lipids . What are Lipids ??. Lipids are organic compounds which are related to fatty acids Lipids are insoluble in water & soluble in nonpolar solvents (fat solvents) such as alcohol, ether, benzene, acetone, chloroform . classification of lipids . Derived Lipids. - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to Lipids
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What are Lipids ??
• Lipids are organic compounds which are related to fatty acids
• Lipids are insoluble in water & soluble in nonpolar solvents (fat solvents) such as alcohol, ether, benzene, acetone, chloroform
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classification of lipids
Simple Lipids Conjugated Lipids Derived Lipids
Natural fats waxes•Phospholipids•Galactolipids•lipoproteins
Substances obtained by
hydrolysis of lipids
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Simple lipidsNatural fats
or: (Triglycerides, Triacylglycerols)
• They are esters of 3 fatty acids with the tri-hydroxy alcohol glycerol
• They include two types: Solid at ordinary temperature: FATs Liquid at ordinary temperature: OILs
• Occurrence of neutral fat:1- in plants: e.g. oils of cotton seed, olive, lin seed , palm oil, coconut ….etc2- in animals: e.g. butter, lard etc 3- in marin oils: e.g. oils of sea animals as cod liver
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Chemistry of Triacylglycerols
Triacylglycerols are esters resulting from the reaction of fatty acids & glycerol
CH2- OH R1-COOH CH2-C-R1 I -3 H2O I CH2 – OH + R2-COOH CH - C - R2 I I CH2 – OH R3-COOH CH- C- R3
GLYCEROL + 3 molecules of fatty acids Triacylglycerol
O
O
O
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Chemistry of Fatty Acids
• They are monocarboxylic acids (R- COOH) with: 1- Hydrocarbon chain (R): hydrophobic 2- Carboxyl group (–COOH ): that ionize to –COO- (hydrophilic) so, Fatty acid is an amphipathic molecule i.e. it have both hydrophilic & hydrophobic regions on the same molecule
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1- Saturated Fatty Acids: contain even number of carbon atoms with no double bonds general formula Cn H2n+1 COOH important examples:
Butyric acid: (4C): CH3 - CH2 - CH2 - COOH 4:0 Palmitic acid (16 C): CH3 - (CH2)14 – COOH 16:0 Stearic acid (18C): CH3 - (CH2)16 - COOH 18:0
Classification of Fatty Acids in Nature (according to saturation)
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2-
2- Unsaturated Fatty Acids:
They contain even number of carbon atoms and one or more double bonds
The most important:
Oleic acid (18C) : contains one double bond between C9 & C10 in the chain
CH3-(CH2)7-CH=CH-(CH2)7-COOH 18:1(9)
Linoleic acid (18 C): contains two double bonds between C9 & C10 and C12 & C13
CH3-(CH2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH 18:2(9,12)
Linolenic acid (18 C): contains three double bonds between C9-10 , C12-13 & C15-16
CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH 18: 3 (9,12,15), w3 ( from the methyl carbon end)
Classification of Fatty Acids according to saturation (cont.)
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Essential fatty acids: can NOT be synthesized in human body. So, MUST be supplied with food.
Two fatty acids are dietary essential in humans:
Linoleic acid: precursor of arachidonic acid which is important for prostaglandin synthesis
a-Linolenic acid:
precursor for other w3 (omega3) fatty acids which are important for growth and development
Essential Fatty Acids
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- Fatty acids are highly water-insoluble - So, a fatty acid must be transported in blood in with a protein
1- Fatty Acid Esters > 90% of blood fatty acids are esters i.e. included in triacylglycerol, in cholesterol esters & in phospholipids that are transported in blood with lipoprotein particles
2- Free Fatty Acids (Unesterified) < 10 of blood fatty acids are free (unesterified) i.e. not bound to any other molecule They are transported in blood with albumin.
Transport of Fatty Acids in Blood
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Phospholipids
PL are conjugated lipidsPL are ionic polar structure formed of an alcohol that is attached by
bridge to a back bone either diacylglycerol or sphinogosine
A
hydrophilic head
Long hydrophobic Tail
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Phospholipids & Glycolipids
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Cholesterol
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• It is the major sterol in animal tissues • It is available in cells of the body and in blood • Most plasma cholesterol is in esterified form (bound with a fatty acid attached
to C-3).
• Free cholesterol & esterified cholesterol in blood is transported with a protein in liopoproteins
• Blood cholesterol level is normally 150-250 mg/dl
• High cholesterol levels in blood (HYPERCHOLESTEROLEMIA) may lead to ATHEROSCLEROSIS (i.e. deposition of cholesterol on inner walls of blood vessels)
Cholesterol (cont.)
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• Sources of cholesterol: 1- Diet: in animal sources 2- Synthesis: by liver cells & others
• Excretion of cholesterol: cholesterol is excreted in bile BUT NOT excreted in urine
Cholesterol (cont.)
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Functions of Cholesterol
1- Cholesterol enters in the structure of cell membrane, brain, liver & other
organs
2- Cholesterol is the precursor for vitamin D3
3- Cholesterol is the precursor of steroid hormones 4- Cholesterol is the source of bile acids & salts which are secreted with the bile juice & essential for the digestion of lipids in the intestine
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Plasma Lipoproteins
Plasma lipoproteins are spherical macromolecular complexes of lipids and proteins (apoproteins, apolipoproteins) They include:• chylomicrons,• very low density lipoproteins (VLDL), • low density lipoproteins (LDL) • high density lipoproteins (HDL) • They differ in lipid & protein composition, in size, density & site of origin
• lipoproteins function to keep their component lipids soluble to transport them in plasma
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lipoproteins are composed of lipids & proteins:
1 - a neutral lipid core of hydrophobic lipid (containing triacylglycerol and cholesterol esters) 2 - surrounded by a shell of amphipathic lipids (phospholipids & nonesterified cholesterol)
3 - Then, the outermost layer is amphipathic apolipoprotein (protein) • Amphipathic compounds are oriented so that their polar portions are exposed on
the surface of the lipoprotein thus making the particle soluble in aqueous solution
• The triacylglycerol and cholesterol carried by the lipoproteins are obtained either from the diet (exogenous source) or from de novo synthesis (endogenous source)
Structure of Plasma Lipoproteins
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Structure of Plasma Lipoproteins
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Size & Density of Plasma Lipoprotein Particles
1- Chylomicrons• lowest in density & largest size of all lipoproteins • contains the highest percentage of lipid & the lowest percentage of protein 2- VLDLs & LDLs • are denser, having higher ratios of protein to lipid than chylomicrons
3- HDL • the densest as it contains the highest level of protein to lipid in all lipoproteind
Plasma lipoproteins can be separated - on the basis of their electrophoretic mobility (lipoprotein electrophoresis)
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Plasma Lipoprotein Electrophoresis
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• Chylomicrons: They carry dietary lipids (TG & Cholesterol) & fat soluble vitamins to blood.
• Very low density lipoproteins (VLDL) is to carry lipid from the liver to tissues.
• Low density lipoproteins (LDL) transfers cholesterol from blood to tissues (originated from VLDL in blood).
• High density lipoproteins (HDL): HDL takes cholesterol from peripheral tissues and transfers it to liver.
Functions of plasma lipoproteins