introduction to lipids structure & functions
DESCRIPTION
Introduction to Lipids Structure & Functions. Objectives. Functions of lipid compounds Clinical problems Lipid compounds of physiological importance Complex lipids: Phospholipids, lipoproteins and glycolipids. - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to Lipids Introduction to Lipids Structure & FunctionsStructure & Functions
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Objectives
Functions of lipid compounds
Clinical problems
Lipid compounds of physiological importance
Complex lipids:
Phospholipids, lipoproteins and glycolipids
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Lipids are heterogeneous groupheterogeneous group of water-water-insoluble molecules related to fatty acids.insoluble molecules related to fatty acids.
They are soluble in non-polarsoluble in non-polar (organic solvents (benzene, ether , chloroform & acetone).
B/c they are insoluble:1.Compartmentalized
( membrane- associated lipids or as TAG in adipocytes.
2.Associated with proteins lipoproteins
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Lipids’ve many many functionsLipids’ve many many functions :Major source of energy (1g=9kcal)Hydrophobic barrierFat soluble vitamins ( coenzymes, regulationPGs& steroid hrs play a major regulatory roles in body’s homeostasis
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Lipids and Related Clinical Problems
Obesity
Atherosclerosis and hypertension
Coronary heart diseases
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A. Simple Lipids:
B.
Complex Lipids:
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Ionized at pH=7, (pK=4.8)
Long-chain FA the hydrophobicity predominates
Fatty Acids
FA has amphipathic
nature.
CH3(CH2)n COOH
Hydrophobic Hydrophilic
>90% of FA in plasma in the form of esters contained in
lipoproteins.
Low levels of free fatty acids are in tissues, but imp. amn.
maybe found during fasting & starvationfasting & starvation
Free FA’re transported by serum albumin
=hydrocarbon chain (alkyl chain )
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Free Fatty Acids (FFA)
1. Chain length:Short-chain and Medium-ChainLong-Chain e.g., Palmitic acid 16:0Very long-chain e.g., Nervonic acid 24:1
2. Degree of saturation:Saturated: No double bondsUnsaturated: Mono- or poly-unsaturated
Cis- or trans-form3. Branched Vs straight-chain4. Essential fatty acids
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Arachidonic ac. is an essential if linoleic acid is missing.
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Unsaturated FA:•monounsat.( one =)e.g, nervonic ac
•polyunsat. (two=)e.g., linoleic ac. ,(three=) eg α- linolenic ac.,
Addition of double bonds: ↓↓ TmTm
Increase chain length: ↑↑ ↑↑ TmTm
Tm =melting temp/
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Trans F.A.Trans F.A.
Are chemically classified as unsaturated f.a., but behave more like saturated f.a.
They elevate serum LDL & increase the risk of CVS
They don’t occur naturally in plants & occur in small amounts in animals
Trans f.a. are formed during hydrogenation of liquid vegetable oils (margarine)
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The presence of bouble bonds in some of LCFA of membrane FA maintain the fluid fluid nature of those lipidsnature of those lipids
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Free fatty acids cannot Free fatty acids cannot be used as a fuel for be used as a fuel for RBCS & BrainRBCS & Brain
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Saturated FatSaturated Fat
Consumption of saturated fats is strongly associated with high levels of total plasma high levels of total plasma cholesterol & LDL-cholesterolcholesterol & LDL-cholesterol
Thus there is ↑ risk of CVS Main sources: dairy & meat products ,
vegetable oils as coconut & palm oils
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*Phytanic acid’s (3,7,11,15 tetramethyl palmitic ac.) present in ↑↑ in dairy products.
Branched F.A.Branched F.A.
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Triacylglycerols
Storage form in adipose tissue
~ 90% of dietary lipids
Glycerol plus 3 fatty acids
Blood transport: Chylomicrons and VLDL
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Acetone Acetoacetate 3-hydroxybutyrate
1. Water-soluble2. Diabetic Ketoacidosis
Ketone BodiesKetone Bodies:
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Phospholipids & Glycolipids
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PhospholipidsPhospholipids
PL 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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A. GlycerophospholipidsGlycerol-containing phospholipids 1. Phosphatidylcholine (Lecithin)
e.g., Surfactant (Dipalmitoylecithin) 2. Cardiolipin (antigenic) 3. Phosphatidyl inositol (signaling molecule)
B. Sphingo-phospholipids:Sphingosine-containing phospholipids:e.g., sphingomyelin (Myelin sheath)
Phospholipids
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Sphingolipids
The sphingolipids include: sphingomyelinsglycosphingolipids
They are essential components of cell membrane (greatest in nerve tissue).
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Sphingolipids
Sphingosine
Ceramide
Precursor of glycolipids
Ceramide: Parent Sphingolipid Compound
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A sphingomyelin
Alcohol at C-1 is esterified to Phoshorylcholine
Important constituents of myelin in
nerve fibers
The only significant sphingolipids in humans
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Clinical Significances of Glycosphingolipids
present in the outer leafletouter leaflet of the plasma membrane.
carbohydrate moieties of glycolipids : antigenic determinants on the surfaces of cells
(e.g.,blood group antigens.) cell surface receptors GM1 sources of various embryonic antigens
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Cholesterol Structure
Sterols: are steroids with 8-10 carbon atoms in the side chain at C-17 & OH at C-3 Cholesterol is the major sterol in animal tissuesIt is a sterol (with 8 carbons at C17,= bet 5&6)
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Overview and Functions
Major Sterol of animal tissues Component of cell membranes Precursor for:
Bile acids & saltsVitamin D Steroid hormones:
Mineralocorticoids e.g., AldosteroneGlucocorticoids, e.g., CortisolSex hormones, e.g., Testosterone
Estrogen & progesterone Hypercholesterolemia: Atherosclerosis & CAD
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Cholesterol: Types
Free cholesterol Esterified cholesterol
OH at C3HydrophobicMembranesPlasmaTransport
FreeLessFoundLessLDL/HDL
Fatty acidMoreAbsentMostHDL/LDL
CONT’D
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Lipoprotein Structure
Protein part: Apoproteins or apolipoproteinsAbbreviations: Apo-A, B, CFunctions:
Structural and transport functionEnzymatic functionLigands for receptors
Lipid part:• According to the type of lipoproteins• Different lipid components in various combinations
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Lipoprotein StructureLipoprotein Structure
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Chylomicrons
Very low densityLipoprotein (VLDL)
Low densityLipoprotein (LDL)
High density Lipoprotein (HDL)
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Plasma Lipoproteins
Triacylglycerol transport: Chylomicrons: TG of dietary origin VLDL: TG of endogenous synthesis
Cholesterol transport: LDL: Mainly free cholesterol HDL: Mainly esterified cholesterol
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Take Home Message
Lipids are heterogeneous group of compoundsLipids are relatively water-insolubleSimple lipids:
FFA, TG, Ketone bodies, CholesterolComplex lipids:
e.g., Phospholipids, LipoproteinsLipids have important physiological functionsLipid disorders are the basis for common human diseases, namely obesity and atherosclerosis