Lipid Chemistry I Lecture Notes PDF

Course Title :Biochemistry I Course Code :FM104 Department :Biochemistry Lecture Title Lipid Chemistry I Lecturer Name Ass. Prof Dr. Omnia Safwat El-Deeb Lecture Objectives: Each student at this lecture should be able to: Define lipids Recognize importance o...

Course Title :Biochemistry I Course Code :FM104 Department :Biochemistry Lecture Title Lipid Chemistry I Lecturer Name Ass. Prof Dr. Omnia Safwat El-Deeb Lecture Objectives: Each student at this lecture should be able to: Define lipids Recognize importance of lipids Know the structure of fatty acids Identify the classifiaction of fatty acids Contents: Lipids definition and functions Classifications of lipids Structure of fatty acids Classification of fatty acids - Nutritional value - Omega classification - Saturation - Chain Length  Definition: O Lipids are heterogeneous group of ORGANIC compounds that are insoluble in water while O They are soluble in nonpolar organic solvent (ether, chloroform, petroleum, benzene, alcohol) O The hydrophobic (water-hating) nature of lipids is due to the predominance of hydrocarbon chains in their structure.  Biochemical importance of lipids  In Diet: They provide the body with the Essential fatty acids.  They serve as a source of Fat soluble vitamins.  Provide the body with high amount of Energy.  In the Body: 1. It is important storage form of energy (one gram fat produces about 9 Kilocalories). 2. It provides the body with 7-dehydrocholesterol which is converted into vitamin D3 by exposing to U.V light. 3. It acts as heat insulator ( protect the body from heat loss) 4. Formation of important derivatives: ( Bile salts, Hormones, lipoproteins) 5. It supports some internal organs e.g. kidney.  1- Simple lipid: Definition: O They are esters of fatty acids with various alcohols (Ester bond = -COO-). O They are either fats or waxes. O II. Complex Lipids They are esters of fatty acid with alcohols having additional groups. Depending on the additional groups, they are classified into: Phospholipids: (lipid + phosphatidic acid) Glycolipids: (lipid + carbohydrates) Lipoproteins: (lipid + proteins) III. Precursor and derived lipids: Substances which are given by hydrolysis of simple & complex lipids - Steroids. - Carotenoids. - Ketone bodies. - Fat soluble vitamins  Fatty acids O Definition: They are aliphatic, linear monocarboxylic acid. O Structure: General structural formula of fatty acid is R-COOH R group is the aliphatic (non-branched) hydrocarbon chain and accounts for the nonpolar nature of fat The carboxyl group of the fatty acids is polar or hydrophilic Structure of Fatty Acid Non Polar Polar Water insoluble Water soluble O Amphipathic molecule O Polar carboxyl group O Non-polar hydrocarbon tail Starting from carbon atoms adjacent to the carboxylic carbon (the α- carbon, β, γ…. etc.) The terminal methyl carbon (CH3) is known as the ω carbon, (ω1, ω2, ω3…..etc) Numbering the carbon atoms in fatty acid Numbering 8 Carbon atoms fatty acid I. Dependingon thechain length Short chain fatty acid: (2 -10 carbons atoms) - Acetic acid (C2): CH3-COOH - Propionic acid (C3): CH3- CH2-COOH - Butyric acid (C4): CH3- CH2-CH2-COOH - Valeric acid (C5):CH3- CH2-CH2-CH2-COOH Long chain fatty acid: (more than 10 carbon atoms.) e.g.: - Palmitic acid (C16): CH3-(CH2)14-COOH - Stearic acid (C18): CH3-(CH2)16-COOH  II. Depending on the presence of double bond (Saturation level) 1-Saturated fatty acid: ( no double bond in the hydrocarbon chain) -------------------------------- 2- Unsaturated fatty acid: (at least one double bond): The systemic name end by the suffix (-enoic) e.g. Oleic acid  A. According to number of double bonds unsaturated fatty acids are classified into: 1-Monounsaturated fatty acid with one double bond: Palmitoleic acid C16: C16:1Δ9 (ω 7): CH3-(CH2)5-CH=CH-(CH2)7-COOH Oleic acid C18 C18: 1Δ9 (ω 9): CH3-(CH2)7-CH=CH-(CH2)7-COOH. They are nonessential because they can be formed in the body by desaturase enzyme. Palmitic acid desaturase Palmitoleic acid. Stearic acid desaturase Oleic acid C18: 1Δ9 (ω 9): CH3-(CH2)7-CH=CH-(CH2)7-COOH. Oleic acid  Palmitoleic acid C16: C16:1Δ9 (ω 7): CH3-(CH2)5-CH=CH-(CH2)7-COOH Oleic acid C18 C18: 1Δ9 (ω 9): CH3-(CH2)7-CH=CH-(CH2)7-COOH. 2- Polyunsaturated fatty acid with more than one double bond e.g.  Sources of arachidonic acid O 1) Diet which directly supply arachidonic acid. O 2) Dietary linoleic is converted in the body into arachidonic. O3) Membrane phospholipids which release arachidonic acid by phospholipaseA2 Eicosanoids: - These compounds, derived from eicosa- (20-carbon) polyenoic fatty acids, comprise Prostanoids, Leukotrienes (LTs), and Lipoxins (LXs). - Prostanoids include Prostaglandins (PGs), Prostacyclins (PGIs), and Thromboxanes (TXs) - COX-derived eicosanoids such as prostaglandins (PGs) and thromboxanes (TXs) have important roles as they are involved in regulation of cardiovascular function and tumor progression - LO-derived eicosanoids such as the leukotrienes (LTs) have been implicated as important mediators of inflammation & asthma  Cis and Trans fats - Cis fatty acid has both hydrogen atoms located on the same side. On the contrary, trans fatty acid has the two hydrogen atoms on opposite sides. - Cis fats are typically considered better for the body than trans fats. Cis fats is associated with good cholesterol in the body. Trans fats can clog arteries and increase levels of bad cholesterol.  III. Depending on nutritional value 1- Non-essential Fatty acids: O They are synthesized in the body and include all saturated and monounsaturated. O They can be formed in the body by Δ9 desaturase enzyme system in liver. 2- Essential fatty acids: A. Definition: O 1. These are fatty acids that cannot be synthesized in the body. They must be obtained from the diet. O 2. They include fatty acids that contain more than one double bond (polyunsaturated fatty acids), eg. lenoleic, lenolenic and arachidonic acids. O 3. The human body has no enzyme system that can form more than one double bond. O N.B. Humans lack the enzymes that can introduce double bond beyond 9th carbon IV. Depending on Omega/Delta nomenclature classification Questions 1. Classify Lipids 2. Enumerate 3 essential fatty acids and write their chemical structure 3. Write the biomedical importance of lipids References: 1-Lippincott’s: Illustrated Review Biochemistry. 2-Harpers Illustrated Biochemistry Thank You SUE