introduction to lipids structure & functions
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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
Introduction to Lipids Introduction to Lipids Structure & FunctionsStructure & Functions
Objectives
Functions of lipid compounds
Clinical problems
Lipid compounds of physiological importance
Complex lipids:
Phospholipids, lipoproteins and glycolipids
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
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
Lipids and Related Clinical Problems
Obesity
Atherosclerosis and hypertension
Coronary heart diseases
A. Simple Lipids:
B.
Complex Lipids:
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 )
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
Arachidonic ac. is an essential if linoleic acid is missing.
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/
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)
The presence of bouble bonds in some of LCFA of membrane FA maintain the fluid fluid nature of those lipidsnature of those lipids
Free fatty acids cannot Free fatty acids cannot be used as a fuel for be used as a fuel for RBCS & BrainRBCS & Brain
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
*Phytanic acid’s (3,7,11,15 tetramethyl palmitic ac.) present in ↑↑ in dairy products.
Branched F.A.Branched F.A.
Triacylglycerols
Storage form in adipose tissue
~ 90% of dietary lipids
Glycerol plus 3 fatty acids
Blood transport: Chylomicrons and VLDL
Acetone Acetoacetate 3-hydroxybutyrate
1. Water-soluble2. Diabetic Ketoacidosis
Ketone BodiesKetone Bodies:
Phospholipids & Glycolipids
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
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
Sphingolipids
The sphingolipids include: sphingomyelinsglycosphingolipids
They are essential components of cell membrane (greatest in nerve tissue).
Sphingolipids
Sphingosine
Ceramide
Precursor of glycolipids
Ceramide: Parent Sphingolipid Compound
A sphingomyelin
Alcohol at C-1 is esterified to Phoshorylcholine
Important constituents of myelin in
nerve fibers
The only significant sphingolipids in humans
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
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)
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
Cholesterol: Types
Free cholesterol Esterified cholesterol
OH at C3HydrophobicMembranesPlasmaTransport
FreeLessFoundLessLDL/HDL
Fatty acidMoreAbsentMostHDL/LDL
CONT’D
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
Lipoprotein StructureLipoprotein Structure
Chylomicrons
Very low densityLipoprotein (VLDL)
Low densityLipoprotein (LDL)
High density Lipoprotein (HDL)
Plasma Lipoproteins
Triacylglycerol transport: Chylomicrons: TG of dietary origin VLDL: TG of endogenous synthesis
Cholesterol transport: LDL: Mainly free cholesterol HDL: Mainly esterified cholesterol
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