LEC.1, LIPIDS Lecture Notes PDF

040817203 (Structure and Function of Biomolecules) LIPIDS By: Aliaa A. Masoud, PHD Lecturer of Biochemistry, Faculty of Science, Alexandria University  Structure & Functions of Lipids Course Specification The aim of the cou...

040817203 (Structure and Function of Biomolecules) LIPIDS By: Aliaa A. Masoud, PHD Lecturer of Biochemistry, Faculty of Science, Alexandria University  Structure & Functions of Lipids Course Specification The aim of the course is to have the necessary knowledge about the different classes of lipids, including their chemical structure, properties & functions. Biomolecules (Biological molecules)  They are molecules that are produced by a living organism.  Lipids, nucleic acid, carbohydrates, proteins are the 4 main organic biomolecules.  Also Minerals & vitamins are considered as biomolecules.  Biomolecules are the building blocks of life and perform variable important functions in living organisms.  The is a fundamental relationship between structure & function of the biomolecules, which is influenced by factors such as the environment in which a given biomolecule occurs. Outlines  What are Lipids ?  Biological Importance of Lipids  Classification of Lipids  Fatty acids (FAs) I-Saturated Fatty Acids (SFAs) II-Unsaturated Fatty Acids (USFAs) What Are Lipids ? The word lipid is derived from a Greek word “lipos” which means FAT. The term Lipids was first used by the German biochemist Bloor in 1943 for major class of tissue components and food stuffs.  Lipids are heterogeneous group of organic compounds, related to fatty acids, including fats, oils, waxes and others. Oily, greasy, relatively insoluble in water and other polar solvents while soluble in nonpolar (organic) solvents (ether, chloroform, benzene, acetone). Hydrophobic in nature because of the predominance of hydrocarbon chains (–CH2– CH2–CH2–CH2–) in their structures. Their general chemical composition includes C,H & O (P,N, S) atoms as H:O ratio = 2:1 (hydrophobic). Unlike the other macro-biomolecules, lipids are not polymers – they aren’t composed of monomers. What Are Lipids ? They are widely distributed in nature both in plants and animals. Represent 18-25% of adult body mass. In our body, lipids are found primarily in three compartments: plasma, biological membranes & adipose tissue. Adipose tissue: is a loose connective tissue designed to store fat (in adipocytes: fat cells), found under skin, around kidney, with in abdomen & breast. Providing reserve food fuel Insulating against heat loss Supporting & protecting organs Biological Importance of Lipids  Structural element of biological membranes and nerves (glycolipids, phospholipids, sphingomyelins, cholesterol & lipoproteins) and maintains membrane fluidity.  Energy reservoir: storage lipids are the chief storage form of energy in body, as lipids are more palatable, storable to unlimited amount compared to carbohydrates as they are reduced and anhydrous. Their oxidation yield twice the amount of energy produced by carbohydrates. Thermal insulator in the subcutaneous tissues, insulating body against heat loss.  Fixation & protective cushion for internal organs, protective coat for many organisms. Biological Importance of Lipids Cell-cell adhesion, Cell recognition & Tissue immunity (glycolipids). Surfactants & Emulsifying agents, help in dietary fat digestion, absorption (Bile acids, Lecithins). Cellular metabolic regulators, modulators & intracellular messengers (Steroid hormones, Prostaglandins, inositol triphosphate I3P). Provide body with fat-soluble vitamins (A,D,E & K) and essential fatty acids. Components of the electron transport chain (Ubiquinone:Coenzyme Q). Classification of Lipids i. Saponification Classification System Based on particular chemical reaction (Saponification) that lipid undergoes Ester hydrolysis basic condition (KOH) Saponifiable lipids Non-Saponifiable lipids Triglycerides Steroids Waxes Terpenes Phospholipids Vitamins Glycolipids Eicosanoids Classification of Lipids ii. Bloor,s Classification System Based on chemical composition of lipids Fatty Acids (FAs)  They are aliphatic monocarboxylic organic acids (R-COOH): They are hydrocarbon chain with one carboxyl group in one end.  FAs are amphipathic, hydrophilic COOH head with hydrophobic group ( hydrocarbon chain: R).  More than 100 different FAs are present naturally. 90% of FA in body found as esters (not free). And mostly obtained from the natural fats and oils hydrolysis. Fatty Acids (FAs)  General formula CH3(CH2)n-2COOH.  Accordingly, most of FAs have even number of C atoms(4-36), because they are synthesized from condensation of 2C (acetate) units. In biological systems, The most commonly occurring FAs have 12 -24 Cs, odd in rare conditions.  Generally, straight unbranched chain with few exceptions have branched & heterocyclic chains.  According to number of C atoms in the chain length, they are classified into: Short, Medium & Long FAs. Classification of Fatty Acids Chain Length Short 2-6 Cs, Medium 8-10 Cs, Long 10-24 Cs, Very long Nature of Chain Straight, Branched, Cyclic, Substituted Total C Atoms Odd & Even Degree of Saturation Saturated & Saturated Synthesis in Body Essential & Non-essential Straight Chain Fatty Acids  Linear arrangement of C in the alkyl chain.  The most abundant FAs in animals & plants.  According to no. of C atoms : I. Even numbered chain FAs II. Odd numbered chain FAs The most commonly occurring FAs, Rare, found in some plants & marine having even number of Cs (12-24) organisms. As: Palmitic acid(16:0) As: Propionic acid (3:0) Oleic acid (18:1) Heptadecanoic acid, margaric acid (17:0)  According to degree of saturation of the alkyl chain ( presence of double bonds), FAs are sub-classified into: Saturated & Unsaturated I-Saturated Fatty Acids (SFAs)  Fatty acids with straight single bonded hydrocarbon chain (no db).  Arranged in extended conformation packed together in compact structure  According to chain length: a. Short-chain FAs, ≤10 Cs,Water-soluble Volatile, C2-6, liquid at RT. Non-volatile, C8-10, Solid at RT. b. Long-chain FAs, >10 Cs, water-insoluble, non-volatile, solid at RT, occur in hydrogenated oils, animal fats, butter & coconut and palm oils I-Saturated FAs, Nomenclature  Numbering of fatty acid C atoms  Firstly, The carbon skeleton of FAs are numbered either from: the COOH group or from the terminal methyl group (termed omega (ꞷ) carbon).  The C atoms are numbered from the COOH end, which is known as C1 The C atom adjacent to the COO- group is known as C2 or α-C, and the next C as C3 or β-C and the next C 4 or γ-C,…etc.  The methyl C at the other end of FA is known as omega C (ω-C). I-Saturated FAs, Nomenclature  Systematic name (IUPAC) is derived from: 1. Name its parent hydrocarbon, 2. Omit the E ot its end 3. Add the ending suffix oic, that representing saturated FA. I-Saturated Fatty Acids (SFAs)  Palmitic (16:0) & stearic acids (18:0) are the most prevalent SFA in animal cells. The longer R-length of the SFA Greater energy required to reduce hydrophobic interactions between its molecules Higher melting point.