Biochemistry Tutorial 8: Lipids Structure & Classification PDF

Biochemistry – Winter 2024/1 Tutorial 8: Lipids Structue & Classification Nourhan Ihab Elfar, PhD Nihal Moustafa Mansour, PhD Assistant Professor of Biochemistry Assistant Professor of Biochemistry [email protected]...

Biochemistry – Winter 2024/1 Tutorial 8: Lipids Structue & Classification Nourhan Ihab Elfar, PhD Nihal Moustafa Mansour, PhD Assistant Professor of Biochemistry Assistant Professor of Biochemistry [email protected] [email protected] Mohamed Mohamed Naguib, PhD Assistant Professor of Biochemistry [email protected] Tutorial 8 November 6, 2024  Tutorial-4 Contents I. Introduction on Lipids : ✓ Definition. ✓ Solubility: Hydrophobic & Amphipathic Natures. II. Importance of Lipids : ✓ Lipids Vs. Carbohydrates as Energy Source. III. Fatty Acids : Building Blocks ✓ Saturated Vs. Unsaturated Fatty Acids. IV. General Classification : ✓ Simple, Compound, & Derived Lipids. V. Common Examples : ✓ Simple Lipids: Triacylglycerol (TAGs). ✓ Compound Lipids: Phospholipids & Glycolipids. ✓ Derived Lipids: Cholesterol. 2 Lipids: The Second Class of Biomolecules II Lipids (Fats) 3  I. Lipids: Definition & Solubility ❑ Definition: “Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms, which form the framework for the structure and function of living cells.” ❑ Solubility: A- Hydrophobic Nature: “These organic compounds are nonpolar hydrophobic molecules, which are soluble only in nonpolar solvents (alcohol, chloroform, benzene, etc.) and insoluble in water because water is a polar molecule”. The hydrophobic nature of lipids stems from the many nonpolar covalent bonds. Water, on the other hand, has polar covalent bonds and mixes well only with other polar or charged compounds. 4  I. Lipids: Definition & Solubility B- Amphipathic Natue: ✓ Amphipathic (or Amphiphilic) Nature of Lipids—that is, they have a hydrophilic (“water-loving”) or polar end (head) and a hydrophobic (“water-fearing”) or nonpolar end (tail). Examples: ✓ Phospholipids are specialized lipids that are partially soluble in water. This dual nature allows them to form structures called membranes which surround all living cells. All of the lipid molecules in cell membranes (phosphoipids) are amphipathic. ✓ Glycolipids. ✓ Cholesterol. 5  II. Importance of Lipids 1. Important Storage Form of Energy (Mainly TAGs). They give 9 Calories/ gram. 2. Structural Components: Important Constituents of Cell Membranes. 3. Help in Absorption of Fat Soluble Vitamins (A, D, E, and K). 4. Precursor for vitamin D synthesis (From cholesterol). 4. Important Constituent of Nervous Tissue. 5. Serve as a Thermal Insulator in the Subcutaneous Tissues. 6. Essential for Maintaining Cellular Integrity. 7. Act as Metabolic Regulators (Steroid Hormones) & Emulsifying Agents (Amphipathic Lipids). 6  II. Importance of Lipids: Lipids Vs. Carbohydrates as energy source Q; Why lipids (TAG; Triacylglycerol) is chosen , other than carbohydrates (glycogen), by our body as a fuel reserve during growth ? Answer: TAG stores allow survival for several weeks. While, glycogen sustain physiological function for about 24 hours due to the following criteria. Lipids Stores Carbohydrates Stores  III. Fatty Acids: Building Blocks ❑ Definition: ✓ Fatty acid is the building block of lipids. It is made from carboxylic group (-COOH) and hydrocarbon chain (-R). ❑ Classification: ✓ Fatty acids are classified into: 1. Saturated F.As (with single bonds only). 2. Unsaturated F.As (with at least one double bonds), that is further classified into Mono- and Poly- Unsaturated F.As according to the number of double bonds between carbon atoms. 8  IV. Classification of Fatty Acids ❑ According to the presence of double bonds (degree of unsaturation): 9  IV. Classification of Fatty Acids ❑ ∆n (indicate the position of the double bond) where n is the lower numbered carbon in the double bonded pair. ❑ The double bonds of polyunsaturated fatty acids are separated by CH2 (methylene) group so, they are not conjugated. ❑ The configuration of the double bonds in fatty acids is cis- (Same direction). ❑ The length of the hydrocarbon chain of a fatty acid and its degree of unsaturation affects the melting point. A). as number of carbon increases, the melting point increases (solid at room temperature). B). as the number of double bonds increases, the melting point decreases (liquid at room temperature). 10  Fatty Acids: Saturated Vs. Unsaturated Vs. 3 Structure I. State II. Health Unhealthy Fats: Increase the risk for coronary heart Healthier Fats: Decrease the risk for coronary heart III. disease. disease. 11  IV. Classification of Fatty Acids ❑ According to the nutritional importance (Biological classification): ω carbon is the carbon atom at the end of the hydrocarbon chain of a fatty acid. Nomenclature of unsaturated fatty acids with respect to ω carbon is as follows: [Number of carbons in the hydrocarbon chain of the fatty acid – Position of the last double bond in the fatty acid]. 12  V. General Classification of Lipids F.A.+ Alcohol + Possess F.A.+ Alcohol Results from Additional group characteristics of hydrolysis of lipids simple or compound lipids Cholesterol 13  VI. Common Examples-Simple Lipids ✓ Among simple lipids, two common examples are TAGs & Waxes. ❑ Triacylglycerol (TAGs) Esters of fatty acids with glycerol. Neutal fat. Most of edible fats are TAGs. Fat in liquid state is called Oil. ** Function of TAGs: TAGs are primarily stored in adipose tissue and serves as main energy storage. TAG is not a constituent of cell Structure of Triacylglycerol membrane as it lacks polar head groups. (TAG) 14  VI. Common Examples-Simple Lipids ❑ Fats and Oils that are widely distributed in both plant and animal tissues are chemically Triacylglycerols (TAGs). Liquid TAGs Solid TAGs 15  VI. Common Examples- Compound Lipids ✓ Among compound lipids, two common examples are Phospholipids & Glycolipids. A. Phospholipids: ▪ General Structure: F.A. + Alcohol + ▪ Classification: According to alcohol Phosphoric acid + Nitrogenous base (NB) present, it is further classified into Glycerophospholipids & Sphingophospholipids. 16  VI. Common Examples- Compound Lipids Phospholipids Importance 1. Major Lipid Constituents of Cellular Membranes and Myelin Sheath. 2. Serve as Good Emulsifying Agents and Help in Intestinal Absorption of Lipids. 3. Important Constituent of Lipoproteins. 17 VI. Common Examples- Compound Lipids B. Glycolipids: ▪ General Structure: ▪ Classification: According to carbohydrate present, (F.A. + Sphingosine) it is further classified into cerebrosides & Ceramide + gangliosides. Carbohydrate Cerebrocides Gangliosides (Simple) (Complex) 18  VI. Common Examples- Compound Lipids Cerebrosides (Simple Glycolipids) ✓ It acts as precursors for synthesis of more complex glycolipids (Gangliosides). ✓ According to the CHO moiety present it is divided into: a. Galactocerebrosides is found in high concentration in nerve tissue membrane. b. Glucocerebrosides is found in non-neural tissues. 19 VI. Common Examples- Compound Lipids Cerebrosides Vs. Gangliosides 20  VI. Common Examples- Compound Lipids Glycolipids Importance 1. Important constituent of cell membrane and nervous tissue (brain) in the body. 2. Constituents of cell surface receptors. 3. Have been identified as a source of blood group antigens. 21  VI. Common Examples- Derived Lipids ✓ Derived lipids include cholesterol, steroids, and prostaglandins etc... ❑ Cholesterol ❑ General Structure ✓ Cholesterol, a class of steroid containing 27-carbon atoms. ✓ The steroid nucleus consists of three six-membered rings (Phenantherene; rings A, B, and C) attached to one five-membered D- Cyclopentano-perhydro- ring (Cyclopentane). Phenatherene (CPPP) 22  VI. Common Examples- Derived Lipids Cholesterol Importance Cholesterol 1. Structural constituent of cell membranes and plasma lipoproteins. 1. Precursor for Steroid Hormones including; * Glucocorticoids (e.g. Cortisol). * Mineralocorticoids (e.g. ADH). * Androgens (male sex hormones). * Estrogens (Female sex hormones). * Progesterone. 3. Precursor for Vitamin D, that is essential for calcium & phosphate metabolism. 3. Precursor for Bile Salts/Acids, that emulsify dairy fats. 23 THE END