Lipid Chemistry Lecture Notes PDF

Lipid Chemistry Dr. Zainab Abdulelah 2022-2023 Outline  Introduction of lipids  Biological significance of lipids  Classification of lipids  Diseases associated with lipids  Fatty acid  Cholesterol  Glycolipids Introduction of Lipids  Lipids are heterogeneous group of organic compounds t...

Lipid Chemistry Dr. Zainab Abdulelah 2022-2023 Outline  Introduction of lipids  Biological significance of lipids  Classification of lipids  Diseases associated with lipids  Fatty acid  Cholesterol  Glycolipids Introduction of Lipids  Lipids are heterogeneous group of organic compounds that contain carbon, hydrogen, oxygen. They are the same components as carbohydrates, but the level of hydrogen in lipids is higher than carbohydrates.  Lipids yields more energy than carbohydrates for body  They are insoluble in water but soluble in organic solvents like ether, chloroform, benzene and acetone.  human body requirement of lipid 30% from energy requirement  Lipids are widely distributed in plants and animals. In plants they are present in nuts and seeds. The lipids depots of animals is subcutaneous and the nervous system of animals is rich in lipids  Food sources rich in lipids are milk, egg, meat, liver, fish, nuts and seeds.  Fatty acids are the major unit of lipids. Biological Significance of Lipids 1.Lipids form one of the three main types of foodstuff and act as fuel in the body. 2.Essential fatty acids (unsaturated) reduces inflammation and helps regulate blood pressure which cannot be manufactured in the body. 3.They protect the body from excessive heat or cold. 4. Building materials: breakdown products of fats can be used for building biologically active materials like cholesterol. 5. Vitamins A, D, E and K are fat soluble, hence lipid is needed for absorbing these vitamins. 6. Act to produce hormones. Diseases Associated with Lipids  atherosclerosis  obesity Classification of Lipids Lipids Simple Triacylglycerol Waxes Complex Phospholipids - lecithin - Cephalin - sphingomyelin Glycolipids Other Complex Lipids derived Steroids Fatty acids Choline Fat soluble vitamins ( K, E, D , A) 1. Simple Lipids: They are esters of fatty acids with alcohol. O R C O R OH OH R C O R According to the type of alcohol, they are classified into : A- Triacylglycerol ( TAG) is a simple lipid consist from alcohol (glycerol) and three fatty acids. And its main storage form of fatty acids and chemical energy. B- Waxes is a simple lipid consist from fatty acid esters of long chain mono- hydroxy alcohols such as : Cholesterol. A) Triacylglycerol (TAG) : On hydrolysis, it gives glycerol and 3 free fatty acids G l y c e r o l Fatty acid Fatty acid Fatty acid Triacylglycerol Physical properties of triacylglycerol :  1- insoluble in water  2- at room temperature , thay can be present as :  A- Fats : solid due to high content of long chain saturated fatty acids , animal source e.g : butter. Milk, & cheese.  B- Oils : liquid due to high content of unsaturated fatty acids , plant source e .g olive oil & corn oil.  B – Waxes :  Esters of fatty acides and long chain alcohols such as : Cholesterol . o o Fatty acid Lipids Fatty acids  Fatty acid is the major unit of lipid and is a carboxylic acid with a long aliphatic chain.  Fatty acids are insoluble in water but soluble in fat solvents (organic solvents) like ether, chloroform, benzene, and acetone  The human body is capable of synthesis a saturated fatty acid from carbohydrates Classification of fatty acids in Lipids 1- saturated fatty acids 2- unsaturated fatty acids (also known as essential fatty acids) which are divided into monounsaturated & polyunsaturated fatty acids. A saturated fatty acid is an acid usually from animal origin , solid at room temperature (25 °C), and has no carbon-to-carbon double bonds, e.g., palmitic acid (16c atoms ) A monounsaturated fatty acid is an acid usually from plant origin, liquid at room temperature, and has one carbon-to carbon double bond, e.g., oleic acid. A polyunsaturated fatty acid is an acid usually from plant origin, liquid at room temperature, and has more than one carbon-to-carbon double bond, e.g., (ω6, ω3). Nutritional classification of fatty acids: A- Essential Fatty Acids:  Essential fatty acids are not manufactured by the body and hence should be taken in diet e.g., linoleic acid & α-linolenic acid.  Deficiency of essential fatty acids leads to: - gastrointestinal diseases such as constipation, bloating, & inflammation. - sterility in adults. B- Non-essential Fatty Acids:  They include saturated fatty acids because they are formed in our body in good amounts mainly from carbohydrates. It is not essential to take them in diets. Q:Which is better for human health, saturated or unsaturated Lipids? Sources of Fatty acids Saturated fatty acids Whole milk, cheese, egg yolks, chicken skin, red meat, ice cream, butter, chocolate ; coconuts , coconut milk , coconut oil. Monounsaturated fatty acids Olives, olive oil, sesame oil, canola oil, peanut oil, cashews, almonds, and avocados. Polyunsaturated fatty acids Sunflower oil, cotton seed oil, Corn, soybean, fish Omega-3 fatty acids are found in Mackerel, salmon, tuna, & Cod Omega-6 fatty acids are found in palm oil, soybean, & sunflower oil. Functions of Dietary Fats 1. Concentrated sources of energy (9 Kcal/g vs.4 Kcal/g for carbohydrates and proteins ) 2. Carriers of fat-soluble vitamins A, D, E, K 3. Sources of Essential Fatty Acids e.g., linoleic acid & α- Linolenic acid 4. Satiety value 5. Impart taste and flavor to foods Chemical Reactions of Fatty Acids 1- Ester Formation 2- Salt formation 3- Reduction 4- Rancidity: • It is the development of bad odor and taste (bad flavor) of fats and oils. • Rancidity is due to exposure of fats or oils to high temperature, oxygen, moisture, light, and metals (which act as catalysts). Health benefits of ω3 fatty acids: 1- Higher intakes are associated with low risk of cardiovascular disease. 2- Reduce blood triglyceride levels. 3- May be helpful in treatment of depression and other psychiatric diseases. 4- May reduce requirements of anti-inflammatory medications in patients with arthritis. 2- Complex Lipids A. Phospholipids (contain phosphate group) E.g. : o Sphyngolipids such as sphingomyelin (sphyngosine + FA + phosphocholine) o Phosphatidylcholine o Phosphatidylethanolamine B. Glycolipids contain fatty acid ,sphingosine and carbohydrate C. Other complex Lipids Lipoproteins, Sulfolipids, & Aminolipids Phospholipids: - Phospholipids are similar in structure to triacylglycerols except that one fatty acid has been removed and replaced by phosphate group. - sources of phospholipids are sunflower ,chicken, eggs ,bovine milk . - examples of phospholipids are lecithin, cephalin, & sphingomyelin. Importance of phospholipids:    phospholipids are required for construction of biological membranes . They are the most abundant lipids in cell membranes. Phospholipids are important constituent of plasma lipoproteins which act as carriers of triglycerides and cholesterol. Lung surfactant is formed mainly of phospholipids, the lack of which is responsible for respiratory distress syndrome in premature infants because the role of pulmonary surfactant is to prevent alveolar collapse. Sphingomyelins : Present in brian, nerves, & plasma membrane . Consist of : Sphingosine + Fatty acid + phosphate + Choline Glycolipids :  They are found mainly in the myelin sheath and cell membrane of RBCs .  They act as cell membrane receptors for hormones and external stimuli, also they provide recognition properties . Lipoproteins  They are complex spherical particles consisting of central hydrophobic lipid core (triglycerides and cholesterol esters) surrounded by hydrophilic membrane consisting of apolipoprotein, phospholipids, and free cholesterol.  These lipoproteins play a key role in the absorption and transport of dietary lipids by the small intestine, in the transport of lipids from the liver to peripheral tissues, and the transport of lipids from peripheral tissues to the liver and intestine. Classification and functions of lipoproteins Cholesterol  Cholesterol is white waxy compound  It is the most important animal sterol. It is present either free (non esterified) or esterified with fatty acid to form cholesteryl ester. Free cholesterol contains 27 carbon atoms.  Distribution of cholesterol: It is widely distributed in all tissues but higher concentrations are present in brain, nerves, liver, skin, and adipose tissue. Important biological functions of cholesterol : 1- One of the important members of membrane lipids. 2- It can be oxidized in the liver into 7-dehydro cholesterol which can be converted under the skin into vitamin D3 by ultra violet (UV). 3- Forms Adrenal hormones 4- Forms Bile acids and salts. Excess cholesterol leads to its precipitation in the gall bladder forming gall stones: 5- Hypercholesterolemia can lead to atherosclerosis which- in turn- may lead to cardiovascular and cerebrovascular diseases.  What foodstuffs contain high cholesterol? - Egg, butter, animal fat, meat Desirable Blood Cholesterol Levels: 1- Total cholesterol Less than 200 mg/dL 2- LDL ("bad" cholesterol) Less than 100 mg/dL 3- HDL ("good" cholesterol) 40 mg/DL or higher 4- Triglycerides Less than 150 mg/dL