Introduction & Classification of Lipids PDF

# Introduction & Classification of Lipids Dr. Uzma Nasib ## Learning Objectives By the end of the lecture, students will be able to know about: - Lipids - Classification - Biochemical function ## LIPID CHEMISTRY ### Definition Organic substances relatively insoluble in water but soluble in or...

# Introduction & Classification of Lipids Dr. Uzma Nasib ## Learning Objectives By the end of the lecture, students will be able to know about: - Lipids - Classification - Biochemical function ## LIPID CHEMISTRY ### Definition Organic substances relatively insoluble in water but soluble in organic solvents like chloroform, ether and benzene. ## FUNCTIONS OF LIPIDS A diagram of a circle with the word *Lipids* in the centre and six smaller circles connected to it with arrows, each representing a different function of lipids: - **Other functions** - **Flavour & Taste to food** - **Absorption of Vitamins** - **Electrical & Thermal Insulators** - **Metabolic regulator** - **Storage form of energy** ## Functions - Precursor of bile acids, steroid hormone - Precursor of vit-D, ecosinoids - Provide thermal insulation - Insulation to the nervous system against atmospheric heat and cold - Anatomical stability to internal organs, protect them from physical shock - Under skin prevent excessive loss of water and electrolytes - Help in transportation of fat soluble vitamins - Protect the body against the injurious effects of water soluble substances - Involved in metabolism and cell signaling. Neural tissue (including the brain) contains relatively high amounts ## Classification of Lipids Lipids are classified into: - **Simple Lipids** - Image depicting oil and butter - **Complex Lipids** - Image depicting a cell - **Derived Lipids** - Image depicting a blood vessel ## Simple Lipids They are esters of FA with various alcohols. Based on the type of alcohols present, these are subclassified as: - **Neutral fats or oils:** Alcohol is **GLYCEROL** - **Waxes:** Alcohol is **other than glycerol** - Includes natural fats and waxes - A diagram depicting a glycerol molecule with three fatty acid chains attached to it labelled as *Triglyceride*. - **Numbers of OH of glycerol differentiate these acylglycerols into mono, di and triacylglycerol.** - A diagram depicting the structure of triacylglycerol and monoacylglycerol. A separate diagram depicts the structure of four fatty acids: - C16:0 - C18:0 - C18:1 - C18:2 - Simple fat have simple function - They are neutral lipid - Storage in adipose tissues - Body contouring - Insulation - Store of energy - A diagram depicting a triacylglycerol molecule - Mono and diacylglycerols are important in digestion & as metabolic intermediates. TAGs are major source of storage and transport form of lipids. - TAGs with **different fatty acid composition** are known as **MIXED TAGS**. - A diagram depicting a triacylglycerol molecule with different fatty acid components labelled as: - **lauric acid** - **Myrictic acid** - **Palmitic acid** - **Physical properties of TAGs:** - Liquid or non crystalline solid at RT. - Liquids: Oils - Pure fats & oils are colorless, odorless & tasteless. - Color is due to impurities. Butter (yellow): Carotene - Taste: diacetyl and 3-hydroxy-2-butanone (bacteria). ## Waxes - **Esters of FA with higher molecular weight monohydric alcohols.** - Examples: - Lanolin - Beeswax - Whale sperm oil - **Esters of FA with alcohol, other than glycerol (monohydroxy alcohol).** - Widely distributed both plants and animals. - **Waxes are not hydrolyzed & no nutritional value.** - A photo of honeycomb. - **Functions of Waxes:** - Skin & hair keeps the surfaces pliable & water repellent. - Earwax protects the delicate lining of tympanic membrane from foreign bodies. - Lanolin used as a base for ointments and creams. - Spermaceti used for cosmetics & in candles. ## Complex Lipids - These are esters of FA with alcohol containing **additional [prosthetic] groups.** - **Subclassified according to the type of prosthetic group** - Examples: - **Phospholipids** - **Glycolipids** - **Lipoproteins** ## Compound Lipids - Other substances in addition to FA and alcohol. - A diagram showing a classification of lipids, which includes a branch for **Simple Lipids** with examples: - Wax esters - Sterol esters - Triacylglycerol - A branch for **Complex Lipids** with examples: - **Phospholipids** - Glycerophospholipids - Phosphatidylcholine (PC) - Phosphatidylethanolamine (PE) - Phosphatidylinositol (PI) - **Glycolipids** - Cerebrosides - Gangliosides - A branch for **Derived Lipids** with examples: - Fatty acids - Sterols - Diglycandes - Monoglycerides - **Sphingolipids** - Ceramides - Sphingomyelin ## Derived Lipids - These lipids are derived from the hydrolysis of simple and compound lipids and they possess the characteristics of lipids. - A diagram, depicting a blue triangular shape with small white rectangles containing: - Fatty acids - Steroids - **Cholesterol** - Lipid soluble vitamins & hormones - Ketone bodies ## Functions of Lipids - **Storage form of energy** - **Structural component of cell membrane** - **Precursor of many steroid hormones, vitamin D** - **Act as thermal insulator** - **Protection of internal organs** ## References - [https://www.youtube.com/watch?v= ExVXeo vB6s](https://www.youtube.com/watch?v= ExVXeo vB6s) - Lippincott's Biochemistry - Harper's Biochemistry - Chatter Gee Book of medical Biochemistry # Lipid Peroxidation Dr. Anila Biochemistry JSMU ## Learning Objectives At the end of the lecture, students will be able to: - Define lipid peroxidation and free radicals - Enlist sources of free radicals - Know Mechanisms to induce lipid peroxidation - Enlist Reactive Oxygen Species and Free Radicals - Oxidative stress and Antioxidants ## Lipid peroxidation - Lipid peroxidation is the oxidative degradation of lipids. - It is the process in which free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. - This process proceeds by a free radical chain reaction mechanism. It most often affects polyunsaturated fatty acids. - In addition, end products of lipid peroxidation may be mutagenic and carcinogenic. - Normally, bonds don't split in a way that leaves a molecule with an odd, unpaired electron. - But when weak bonds split, free radicals are formed. - Free radicals are very unstable and react quickly with other compounds, trying to capture the needed electron to gain stability. - Any atom (or atom within a molecule) with at least one unpaired electron in its outermost shell/orbital. - Why do we want to limit their actions? - Highly reactive - Free radicals damage membranes (lipids), proteins, & DNA. - Can result in mutations - **Note:** Radicals are produced as a part of normal metabolism and are necessary to life! Excessive amounts of radicals are harmful because of their reactivity. Also produced by processes outside of normal metabolism (en-adiation, etc.). - **Factors responsible for free radical formation:** - A diagram showing a molecule, which breaks into two free radicals in the presence of heat/light etc. The formation of radicals is called *homolytic cleavage*. - **Free radical reactions:** - Free radicals easily react with a biological molecules (mainly non-radicals) generating new radicals - initiate chain reactions. - PUFA as present in cell membrane are easily destroy by the peroxidation mechanism. - Any free radical involving oxygen can be referred to as reactive oxygen species (ROS). - One of the most important sources of ROS production is mitochondria - **Free radical sources:** - **Exogenous** - Foods - Air pollutants - Radiation - Cigarette smoking - **Endogenous** - Metabolism (mitochondria and peroxisomes) - Detoxification - cytochrome P450 - Immune cells Mechanisms to induce lipid peroxidation - **Photoxidation:** - Singlet oxygen is involved. - Require sensitizers: porphyrins, myoglobin, riboflavin, bilirubin. - **Enzymatic Oxidation:** - Cyclooxygenase and lipoxygenase catalyze the reactions between oxygen and polyunsaturated fatty acids. - **Autoxidation:** - Free Radical Chain-reaction. ## Reactive Oxygen Species and Free Radicals - **Reactive Oxygen Species:** - Radicals: - Superoxide - Hydroxyl radical - Hydroperoxyl radical - Peroxyl - Alkoxyl - Non-Radicals: - Hydrogen peroxide - Hypochlorous acid - Singlet Oxygen - Ozone - Triplet oxygen ## Oxidative Stress - A diagram of a seesaw. One side is labelled as *Prooxidants* and the other is labelled as *Antioxidants*. - “An imbalance favoring prooxidants and/or disfavoring antioxidants, potentially leading to damage” – H. Sies - **Oxidative stress** is an imbalance of free radicals and antioxidants in the body, which can lead to cell and tissue damage. - **Oxidative stress** occurs naturally and plays a role in the aging process. ## Consequences of Lipid Peroxidation - **Structural changes in membranes:** - Alter fluidity and ion channels. - Alter membrane-bound signaling proteins. - Increase membrane permeability. - Suppose a part of cell membrane gets damage by the free radical that whole part of cell membrane or integrity of cell membrane will be lost. ## Pathological Conditions that Involve Oxidative Stress - Inflammation - Atherosclerosis. - Ischemia/reperfusion injury. - Cancer. - Aging. ## Inflammation - A diagram depicting a cycle of inflammation and damage. - Immune cells migrate to the site of inflammation - Produce oxidants to kill bacteria - Oxidants directly damage tissue ## How do you reduce free radicals in your body? - Eat foods rich in antioxidants, chemicals that inhibit the oxidation of molecules by neutralizing free radicals, thereby stopping them from causing cellular damage. - Antioxidants are found in a variety of plants in the form of vitamins A, C and E, selenium and certain phytonutrients and polyphenols. ## FIRST: Oxidants - "First, we need to understand what an oxidant is before we can understand antioxidants." - What is an OXIDANT? - Any atom/molecule that “steals/accepts” electrons from other molecules. - Molecules that promote oxidation. - What is oxidation? - The removal of electrons. ## What is an Antioxidant? - “Substance that prevents or delays oxidation.” - Anti-oxidants prevent or limit the actions of free radicals usually by removing their unpaired electron and thus converting them into something far less reactive. - A diagram depicting an ANTIOXIDANT donating an electron to a FREE RADICAL, stabilizing the FREE RADICAL. - **Antioxidants function by interfering with the chain reaction. If the number of free radicals can be kept low enough, oxidation will not occur.** - **How Antioxidants Reduce Free Radicals:** - **Interrupt the free-radical chain mechanism.** - eg: superoxide dismutase, vitamin E (alpha tocopherol) and uric acid. - **Preventive anti-oxidants:** - They will inhibit the initial production of free radicals. - eg: Glutathione peroxidase, catalase and EDTA. ## Ideal Antioxidants - No harmful physiological effects - Not contribute an objectionable flavor, odor, or color to the product - Effective in low concentration - Fat soluble - Carry-through effect - no destruction during processing - Readily available - Economical - Non-absorbable by the body ## Antioxidant Defenses in Biological Systems - **Fat-soluble cellular membrane consists:** - Vitamin E - Beta-carotene - Coenzyme Q (10) - **Water soluble antioxidant scavengers:** - Vitamin C - Glutathione peroxidase - Superoxide dismutase - Catalase ## Thank You