Lipid Chemistry PDF - Almaaqal University

Almaaqal University Lipid Chemistry Dr/ Wael Sobhy Darwish Biochemistry PhD  Introduction to lipids Definition: Lipids are organic compounds formed from alcohol and fatty acids combined together by...

Almaaqal University Lipid Chemistry Dr/ Wael Sobhy Darwish Biochemistry PhD  Introduction to lipids Definition: Lipids are organic compounds formed from alcohol and fatty acids combined together by ester bond. Lipds are insoluble in water but soluble in organic solvents i.e. ether, benzene, acetone & chloroform. The hydrophobic nature of lipids is due to the predominance of hydrocarbon chains (- CH2-CH2-CH2-) in their structure.  Biomedical Importance of Lipids 1. Source of energy: (Lipids have a high energy value). 2. Structural components of membranes (phospholipids and cholesterol). 3. Metabolic regulators (e.g. steroid hormones). 4. Help in absorption of fat-soluble vitamins (A, D, E and K). 5. Protect internal organs by providing a cushioning effect (pads of fat). 6. Provide insulation against changes in external temperature (subcutaneous fat). 7. Act as electric insulators in neurons Classification of lipids  Simple lipid ❖ Definition: Are esters of fatty acids with various alcohols. (Ester bond = -COO-). They are either fats or waxes Fatty acids are water-insoluble “long chain hydrocarbons” Fatty acids may be Saturated: or Unsaturated: - Fatty acids may be Essential: cannot be synthesized in the body or Nonessential: can be synthesized in the body. - Fatty acids occur mainly as esters in natural fats and oils. - Fatty acids may also present as free fatty acids (FFA) in the plasma. - Short chain F.A : less than 10 C , long chain F.A: more than 10 C  Numbering of carbon atoms: 1. Starting from the carboxyl group: - 1, 2, 3 system: Give COOH No. 1 then proceed to the terminal CH3. - α, β, system: the 1st carbon following COOH is α then proceed to the terminal CH3. 2. Starting from the terminal methyl group (omega “ω” carbon): - The terminal methyl carbon is given ω1 then proceeds to COOH group.  Position of double bonds: The most commonly used systems for designating the Position of double bonds in unsaturated fatty acids are: (1) The delta (Δ) numbering system e.g. palmitoleic acid C16:1Δ9 means that this acid contains 16 carbons (16) and one double bond (1) and the position of double bond is between carbon number 9 and carbon number 10 starting from carboxyl carbon 1. (2) Omega (ω) system e.g. the palmitoleic acid may be written as: C16:1ω7 which indicates a double bond on seventh carbon counting from the ω-carbon atom i.e. last –CH3 carbon.  Saturated & Unsaturated fatty acids i. Saturated fatty acids - Have no double bonds in the chain. - Their general formula is CH3- (CH2) n -COOH where (n) equals the number of methylene (-CH2) groups between the methyl and carboxylic groups. - The systemic name of saturated fatty acids ends by the suffix (-anoic) e.g. palmitic acid (16c) has systemic name hexadecanoic acid (Hexa =6, Deca =10). - Example of the formula of some saturated fatty acids: ▪ Butyric acid (4c) = CH3- CH2- CH2- COOH ▪ Palmitic acid (16c) = CH3 - (CH2)14 - COOH  Unsaturated fatty acids: Contain one or more double bond - Unsaturated fatty acids are either monounsaturated or polyunsaturated. ❖ Monounsaturated fatty acids (monoethenoic, monoenoic) i.e. contain one double bond e.g. palmitoleic acid (16:1 Δ9) and oleic acid (18:1 Δ9). Polyunsaturated fatty acids Containing more than one double bond - PUFA are classified according to the position of the 1st double bond in relation to ω carbon into ω3, ω6, ω7 & ω9 F.A. ▪ ω3 PUFA: PUFA having the 1st double bond at carbon 3 in relation to ω carbon  Essential and nonessential fatty acids: A. Nonessential fatty acids: 1. These are fatty acids which can be synthesized in the body from acetyl COA. Thus they are not necessary to be obtained from the diet. 2. They include all saturated and monounsaturated fatty acids as palmitoleic and oleic acid. B. Essential fatty acids: a) These are fatty acids that cannot be synthesized in the body. They must be obtained from the diet. b) They include fatty acids that contain more than one double bond (polyunsaturated fatty acids) e.g. lenoleic, lenolenic, arachidonic acids. c) The human body has enzyme system that can form only one double bond at the ninth carbon atom  Alcohols: R.OH Alcohols associated with lipids include glycerol, cholesterol and higher alcohols Glycerol: It is alcohol containing 3 (-OH) groups: It combines with one fatty acid to form monoacylglycerol. ▪ Uses of Glycerol: 1. Nitroglycerol is used as a drug for dilatation of coronary artery. 2. Glycerol enters in manufacturing of creams and lotions for dry skin. 3. Glycerin suppositories that enter the body via the rectum, vagina, or urethra.  Simple Lipds They are called simple because they are formed only from alcohols and Fatty acids. There are two classes of simple lipids (according to the type of alcohol): Acylglycerols & Waxes - Acylglycerols are esters of one, two or three fatty acids with glycerol - Waxes: combination of fatty acids +Long chain alcohol They are not digested by lipase enzyme. They are solids at room temperature. Ex: 1. True wax (Bee’s wax): Esters of palmitic acid e’ mericyl alcohol (C30) 2. Lanolin (in hair): Esters of cholesterol derivatives. Triacylglycerols (triglycerides) They are called neutral fat because they carry no charge. Body triacylglycerols: They are stored mainly in cytoplasm of adipose tissue cells Body fat is important source of energy. Each gram fat gives 9.3 calories Dietary sources of triacylglycerols: - In animals e.g; butter and lards. - In plants e.g. Cotton seed oil, linseed oil, sesame oil and olive oil. - Marine oils e.g. cod liver oil and shark liver oil. Types of triacylglycerols: - Simple triacylglycerols: similar 3 fatty acids are attached to glycerol. - Mixed triacylglycerols: 3 different fatty acids are attached to glycerol.  Compound lipids Compound lipids contain in addition to esters of fatty acids with alcohols, other groups. According to the type of the group attached, they are classified into: Compound Lipids Phospholipids Glycolipids Sulfolipids Lipoproteins LIPOPROTEINS IDL  LIPOPROTEINS Because lipids are relatively insoluble in aqueous media, they are transported in body fluids as, often spherical soluble protein complexes called lipoproteins. Lipoproteins can be classified into five main groups. The first three are triglyceride rich and, because of their large size, they scatter light, which can give plasma a turbid appearance (lipidemic) if present in high concentrations: 1- Chylomicrons are the largest and least dense lipoproteins and transport exogenous lipid from the intestine to all cells. 2- Very low-density lipoproteins (VLDLs) transport endogenous lipid from the liver to cells.  3- Intermediate-density lipoproteins (IDLs), which are transient and formed during the conversion of VLDL to low-density lipoprotein (LDL), are not normally present in plasma. The other two lipoprotein classes contain mainly cholesterol and are smaller in size: 4- Low-density lipoproteins are formed from VLDLs and carry cholesterol to cells. 5- High-density lipoproteins (HDLs) are the densest lipoproteins and are involved in the transport of cholesterol from cells back to the liver (reverse cholesterol transport).  Derived Lipids Derived lipids: When both simple and compound lipids combine and undergo the process of hydrolysis, the produced chemical is known as the derived lipids. Derived lipids include cholesterol, carotenes, steroids and prostaglandins, ketone bodies, and Fat soluble vitamins (Vit. K, E, D & A)  Lipid metabolism A. After fatty meal plasma shows a milky appearance. This due to venous blood contains excess chylomicrons after absorption. Excess chylomicrons stimulate mast cells to produce heparin. Heparin then stimulates the blood vessels of heart, lungs, spleen and adipose tissue to produce an enzyme called: lipoprotein lipase (plasma clearing factor). Lipoprotein lipase enzyme will act on triacylglycerols of chylomicrons, converting them into glycerol and free fatty acids.  B. Glycerol and fatty acids are taken up by different tissues for the following fate: 1. Formation of depot fat (adipose tissue). a) It is formed mainly of Triacylglycerols b) It is present in fat cells of adipose tissue. 2. Oxidation for production of energy: a) Fatty acids: Converted into acetyl CoA that is oxidized in citric acid cycle. b) Glycerol: Converted into glycerol-3-phosphate (by glycerol kinase). This is then converted into Dihydroxyacetone phosphate. The later will undergo oxidation in glycolysis. 3. Glucose formation by gluconeogenesis: a) Glycerol → Glucose. b) Odd number fatty acids oxidation → Propionyl CoA → Glucose. 4. Synthesis of biologically active compounds: e.g. different steroids and eicosanoids 5. Synthesis of tissue fats (structural cellular fats)  Fatty acids oxidation 3 Different pathways for fatty acid oxidation are present: α, β and ω. Site 1. Intracellular location: Mitochondria 2. Organ location: a) Liver, kidney, heart and skeletal muscles. b) β-Oxidation never occur in brain can’t pass blood brain barriers and RBCs (no mitochondria) Mechanism 1- Activation of Fatty Acids.