Lecture 11_Lipids PDF

LIPIDS Reymark C. Ereje, RCh, MSc Department of Physical Sciences College of Science University of the Philippines Baguio [email protected] CHEM 40 Lipids Introduction Lipids - biologica...

LIPIDS Reymark C. Ereje, RCh, MSc Department of Physical Sciences College of Science University of the Philippines Baguio [email protected] CHEM 40 Lipids Introduction Lipids - biological compounds insoluble/sparingly soluble in water - Includes the lipid-soluble vitamins (A, E, D, K) Major energy reserves (triacylglycerols: provide 9 kcal of energy/g) For insulation of body organs Structural components of cell membranes Intercellular chemical messengers & aid in lipid solubilization CHEM 40 Lipids Classification based on Structure Simple – ester of fatty acids with various alcohols 1. Natural fats and oils (triacylglycerols) 2. Waxes (a) True waxes: cetyl alcohol esters of fatty acids (b) Cholesterol esters (c) Vitamin A esters (d) Vitamin D esters CHEM 40 Lipids Classification based on Structure Compound lipid - esters of fatty acids with alcohol plus other groups 1. Phospholipids: contain phosphoric acid and often a nitrogenous base 2. Sphingolipids (also include glycolipids and cerebrosides) – contain an aminoalcohol sphingosine 3. Sulfolipids - contain sulfate group 4. Lipoproteins - lipids attached to plasma/other proteins 5. Lipopolysaccharides - lipids attached to polysaccharides CHEM 40 Lipids Classification based on Structure Derived lipids – hydrolytic products of simple & compound lipid with lipid properties 1. Saturated & unsaturated fatty acids 2. Monoacylglycerols and diacylglycerols 3. Alcohols (-carotenoid ring) Beta-carotene CHEM 40 Lipids Classification based on Structure Miscellaneous lipids 1. Aliphatic HC - in liver fat and certain HC in beeswax and plant waxes 2. Squalene - in shark and mammalian liver and in human sebum 3. Vitamins A, D, E and K Squalene Vitamin A CHEM 40 Lipids Lipids with fatty acids Waxes – protective coating lipids Triacylglycerols - energy-storage lipids Phospholipids - membrane Sphingolipids - (structural) lipids Lipids without fatty acids Steroids - messenger Cholesterol – membrane lipid Bile acids – emulsification lipids Cholesterol CHEM 40 Lipids Fatty Acids naturally occurring monocarboxylic acid > long-chain carboxylic acids > insoluble in water > typically 10-20 C atoms (even number) > maybe saturated or unsaturated ( with C=C bond/s) Saturated FA (SFA) Closely packed Strong attractions between chains High melting points Solids at room temperature  fats Monounsaturated FA (MUFA) Polyunsaturated FA (PUFA) Nonlinear chains prevent molecules to pack closely Few interactions between chains Low melting points Liquids at room temperature  oils CHEM 40 Lipids Nomenclature Stearic acid: a typical SFA with 18 C atoms in the chain IUPAC name: octadecanoic acid Oleic acid: a typical MUFA with 18 C atoms in the chain IUPAC name: cis-9-octadecenoic acid CHEM 40 Lipids Nomenclature CHEM 40 Lipids Nomenclature Short-hand for Identifying MUFA and PUFA IUPAC Name Short-hand Common name Linoleic acid, linolenic cis-9-hexadecenoic acid 16:1(9) palmitoleic acid acid and arachidonic cis-9-octadecenoic acid 18:1(9) oleic acid acid are essential FA cis,cis-9,12-octadecadienoic acid 18:2(9,12) linoleic acid cis,cis,cis-9,12,15-octadecatrienoic acid 18:3 (9,12,15) linolenic acid Other PUFA of Biological Importance 20:4 (5,8,11,14) arachidonic acid 20:5 ( 5,8,11,14,17) eicosapentanoic acid (EPA) 22:6 (4,7,10,13,1619) docosahexaenoic acid (DHA) Use of  notation for families of UFA:  - 3 FA  a UFA with its endmost C=C is 3C atoms away from its methyl end Ex. of an  - 6 FA CHEM 40 Lipids Physical Properties of FA 1.↓ solubility in water with ↑ C chain length; solubility in water varies with pH. 2.Insoluble at pH 5, they are converted to salts and exist as carboxylate ions. CH3(CH2)16COOH ↔ CH3(CH2)16COO- + H+ pH 5 3. ↑ melting points with ↑ C chain length. The greater the degree of unsaturation, the greater the reduction in MP greater C=C bonds leads to less efficient Margarine vs. Butter CHEM 40 Lipids Triacylglycerols (TAGs) triesters formed from three fatty acids esterified to the 3 -OH groups of glycerol. - usually R1 and R3 are saturated and R2 is unsaturated - fats and oils are mixture of two or more simple triacylglycerols Fat –solid/semi-solid at RT; generally, from animal sources Oil - liquid at RT; generally, from plants CHEM 40 Lipids Compound: Phospholipids - most common membrane lipids; many are phosphoacylglycerols (structurally related to triacylglycerols but with aminated phosphate group) CHEM 40 Lipids Compound: Sphingolipids contains sphingosine, a fatty acid, and one or more other molecules Sphingosine – a long chain N- containing alcohol Two major types: sphingomyelin glycosphingolipids ex. Cerebrosides CHEM 40 Lipids Cell membrane and Related Structures Micelles -spherical structures - with nonpolar, hydrophobic environment in the core - with polar, aqueous environment on the surface -the bile salt-lipid complexes formed in the small intestines. Bilayers - have polar lipids that have their nonpolar regions facing together, and their polar-head groups facing out into the aqueous solution. CHEM 40 Lipids Cell membrane and Related Structures Fluid Mosaic Model - plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances can move across it - Cholesterol: makes the membrane more stable and prevents it from solidifying - CHO chains attached to the outer surface of the plasma membrane CHEM 40 Lipids Transport across Membranes Membranes - semi-permeable barriers that restrict the movement of ions & polar molecules Simple Diffusion Allows entry & exit of nonpolar molecules Facilitated Diffusion Proteins act as polar channels that allow ions or polar molecules to pass through the membrane. Active transport “uphill” movement across a membrane or against a concentration gradient requires energy CHEM 40 Lipids Lipids without FA Steroids contain the fused-ring system commonly called the steroid nucleus. Cholesterol -most abundant steroid in animals - precursor for the synthesis of other steroids Bile salts - aids in digestion & absorption of dietary -emulsify nonpolar fat globules - have one polar and one nonpolar face. - synthesized from cholesterol in the liver and stored in the gallbladder. CHEM 40 Lipids Lipids without FA Prostaglandins - synthesized from PUFA (derived from arachidonic acid) - play a role in the physiology of fever and pain Leukotrienes - play a role in allergic & inflammation responses. Lipoproteins - complexes of lipids and proteins. - transport lipids in blood. Low-density lipoproteins (LDLs): liver to cells High-density lipoproteins (HDLs): cells to liver CHEM 40 Lipids  Thank you for listening! CHEM 40 Lipids