Lecture 2: Lipids (Biomolecules) - Alexandria University

040817203 (Structure and Function of Biomolecules) LIPIDS lecture 2. By: Aliaa A. Masoud, PHD Lecturer of Biochemistry, Faculty of Science, Alexandria University Agenda  Unsaturated Fatty Acids (USFAs), Isomers  Nomenclature of Unsaturated Fatty Acids  Sources of Unsatur...

040817203 (Structure and Function of Biomolecules) LIPIDS lecture 2. By: Aliaa A. Masoud, PHD Lecturer of Biochemistry, Faculty of Science, Alexandria University Agenda  Unsaturated Fatty Acids (USFAs), Isomers  Nomenclature of Unsaturated Fatty Acids  Sources of Unsaturated Fatty Acids  Classification of Unsaturated Fatty Acids  no. dbs  Position of no. dbs  Body requirements  Physical Properties of Fatty Acids  II-Unsaturated Fatty Acids (USFAs), Isomers  Fatty acids with at least one double bond in their hydrocarbon chain.  USFAs are classified according to the position of H atoms located next to C atoms where the db exists into: Cis [Z] & trans [E] isomers. Cis (Z-zusammen) Trans (E-entgegen)  Oleic & Elaidic acids are cis- & trans-isomers of octadecenoic acid [18:1] [18:1, Z9] [18:1, E9]  II-Unsaturated Fatty Acids (USFAs), Isomers  In nearly all naturally USFAs, the db is in found in cis-configuration: H atoms are on the same side of the bond, steric hindrance causing rigid bend: kink in the aliphatic chain.  Kinks in the molecule do not allow the molecules to stack nicely together. As a result the strength of the van de Walls forces is not as great as in SFAs. Hence these type of molecules are liquid at RT.  As a result, USFAs are loosely packed, easily disrupted by heat, accounting for low melting point.  II-Unsaturated Fatty Acids (USFAs), Isomers  Trans FAs have db but without bent structure, i.e, straight chain like SFA and share high melting point.  Trans FAs are very rare in nature, produced by:  Fermentation in the rumen of dairy animal and obtained from diary products and meat.  During hydrogenation of vegetable oils.  Enzymes in human body that can react with bent, cis-FAs but not trans-isomer. Hence, trans fats build up in body and cause adverse effects.  Nomenclature of Unsaturated Fatty Acids Systematic name (IUPAC) is derived from: 1. Name its parent hydrocarbon, 2. In MSFAs, Omit the ANE of its end, add the ending suffix enoic. 3. In PUSFs, omit NE of end, add the ending suffix(di, tri, tetra, penta,..: according to no. of db) + enoic acid. Monoenoic Polyenoic  Nomenclature of Unsaturated Fatty Acids i. Mono-Unsaturated FAs (MUFAs) Cis -9-hexadecenoic acid Trivial name: Palmitoleic acid (16:1), IUPAC: cis-Hexadecenoic acid Cis-hexadec-9-enoic acid (C atoms : dbs) Configuration USFAs ω- or n-system Delta (Δ)-system Position of db, according to the ω1 of Position of db, according to C1 is COOH- terminal methyl group in the FA. end in the FA.  Represented by the symbol ω followed Represented by the symbol ∆ followed by by number of C of db a superscript number  [16:1: ω-7].  [16:1: ∆9]. Nomenclature of Unsaturated Fatty Acids ii. Poly-Unsaturated FAs (PUFAs) Cis-5-cis-8-cis-11-cis-14-cis-17- ecosapentaenoic acid [EPA] Or:all-cis-5,8,11,14,17- Ecosapentaenoic 20 Cs: Ecosa 5 dbs : penta, in cis-form USF: enoic acid Acc. To ω- or n-system Acc. To Δ- or C- system 20: 5, ω-3 20: 5, Δ 5,8,11,14,17 8  Sources of Unsaturated Fatty Acids The key is consuming the right balance of ω-3,-6, and -9 to support your overall health and wellbeing  Classification of Unsaturated Fatty Acids, acc. to no. dbs  USFA are classified according to no. of db in the back bone into: Monoenoic & Polyenoic A-Mono-unsaturated fatty acids (MUFAs),(mono-ethenoid):  There is a common pattern in the location of dbs.  In most monounsaturated FAs, the db is between C-9 and C-10 (∆9). B-Poly-unsaturated fatty acids (PUFAs):  The other dbs of polyunsaturated FAs are generally ∆12 and ∆15, i.e. separated by methylene group (not alternative), with some exceptions as Arachidonate [20:4(∆5,8,11,14)]  Classification of Unsaturated Fatty Acids, acc. to Position of no. dbs  The molecular structures of PUFAs, the presence of db in the R chain of PUFA introduces a kink in the molecule, creating different secondary structures that influence physical properties.  Classification of Fatty Acids, acc. to Body Requirements A. Non-Essential Fatty Acids  They are formed de novo in the animal body mainly from carbohydrates.  So they are nutritionally nonessential FAs.  These include the saturated FAs and MUFAs.  As: stearic, palmitic, palmitoleic, oleic…  Building blocks of dietary fats Importance  Formation of membrane lipids (phospholipids & glycolipids)  Esterification of cholesterol  Fuel molecules ( energy production)  Classification of Fatty Acids, acc. to Body Requirements B-Essential Fatty Acids (EFAs)  PUFAs cannot be synthesized in our body, because the body lack the enzymes ( Δ12 & Δ15 desaturase) necessary to insert a cis double bond at the n-6 or the n-3 position of a FA.  They should be taken in the diet.  linoleic (LA, ω-6) is the precursor of ω-6 family (AA)  -linolenic acids (ALA, ω-3) is the precursor of ω-3 family (EPA, DHA).  Body can synthesis other PUFAs ( AA, EPA, DHA), if their PRECURSORS EFAs are supplemented in suitable concentrations and appropriate metabolism. Lower efficiency of conversion of ALA into long chain ω-3 PUFAs (EPA & DHA). It is recommended to obtain them from additional sources. Importance of Essential Fatty Acids 6  Maintenance of structural integrity, AA accounts for 5-15% of FAs of phospholipids in membranes.  An important role in blood clotting.  EPA & DHA in retina & brain ( visual & cognitive growth, neurotransmission)  anti-atherogenic effect, by esterification & excretion of cholesterol.  They are essential for skin integrity, normal growth and reproduction. Importance of Essential Fatty Acids,,..  Eicosanoids synthesis including prostaglandins & leukotrienes, thromboxanes, resolving, protectin, lipoxin (biological regulators).  Since the Stone Age, our diet has ensured a balance between ω-6 / ω-3 FAs.  Changes in our eating habits later by the 1960s (consumption of processed foods and industrially prepared dishes, mass consumption of farm animals, increased use of cheap vegetable oils, etc.) have had a negative impact on their ratio.  Physical Properties of Fatty Acids  The length & degree of unsaturation of hydrocarbon chain determined the physical properties of FAs. 1- Solubility Polarity of FAs decreases with :  increasing the length of the non polar hydrocarbon chain accounts for poor solubility of FA.  Fewer double bonds in its chain.  Short-chain FAs are slight soluble due to polarity of –COO- group  Lauric acid (12:0) is more soluble than palmitic (16:0)  Α-linolenic acid (18:3) is more soluble than oleic (18:1). 2- Amphipathic character + pH7 In pH 7, They are ionized into FA anion & H Stearic acid Streate- + H+ 3-Physical state  liquid: Less than 8C.  Solid ( greasy, waxy): more than 12 C  Oily : USFAs  Physical Properties of Fatty Acids 4- Melting point  SFAs, packed in stable aggregates by many hydrophobic interactions in its usual extended conformation, so they have high melting point. While, USFAs (cis-) with one or several such kinks cannot pack together as tightly as fully SFAs, and their interactions with each other are therefore weaker, causing lower melting point and poor ordered arrays.  MP of Lauric acid (12:0) is 44, while palmitic (16:0) is 63  MP of Palmitoleic (16:1) is -0.5, arachidonic acid (20:4) is -49.5 ( required less energy to disorder the array of its molecules)