Lipids Reviewer PDF

**BIOCHEMISTRY: LIPIDS** **CHARACTERISTICS OF LIPIDS** - An organic compound [ ] found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents. - Lipids do not have a common structural features that serves as the basis f...

**BIOCHEMISTRY: LIPIDS** **CHARACTERISTICS OF LIPIDS** - An organic compound [ ] found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents. - Lipids do not have a common structural features that serves as the basis for defining such compounds. - Lipids are present in humans, animals, plants and micro-organisms to some extent. - Also serve as a ***"source of energy''.\ *** - **[Fat]** : Is an ideal form for storing energy in the human body compared to carbohydrates and proteins. - **[FATS]**: They are esters of fatty acids with glycerol. They are also called as **triglycerides** or **triacylglycerols** because all the three hydroxyl groups of glycerol are esterified. Fats are also called as neutral fats. - **[TRIGLYCERIDE]**- is example of fat also known as energy storage. - A lipid is a fat-like substance but need not be a fatty acid always. - ***Classification:*** They are classified on the basis of solubility not on any functional groups. - Lipid molecules often combine covalently to other biomolecules to form hybrid biomolecules such as glycolipids and lipoproteins. - **[GLYCOLIPIDS-]** Combination of carbohydrates and Lipids. - **[LIPOPROTEIN-]** Combination of Lipids and Protein. - Disturbances in lipid metabolism are known to accompany a variety of disease states, especially heart disease and obesity. - Lipids exhibit structural diversity - Some are esters, some are amides, and some are alcohols (acyclic and cyclic) and some are polycyclic. **CHEMICAL NATURE OF LIPIDS** - Lipids are the group of greasy organic compounds, which are soluble in organic solvents. - **[Insoluble in water\ ]** - **[Lipids are hydrophobic\ ]** - They are fats, waxes, compound lipids, steroids, fatty acids and fat soluble vitamins. **[FUNCTION OF LIPIDS]** - Energy-storage lipids- TRIGLYCERIDE - Membrane lipids-SPHINGOGLYCOLIPID, PHOSPHOLIPID, CHOLESTEROL - Emulsification lipids -- BILE ACID - Chemical messenger lipids\ STERIODS, HORMONES - Protective-coating lipids\ BIOLOGICAL WAX **CLASSIFICATION OF LIPIDS -BASED ON THE COMPOSITION** (Simple lipids, Compound lipids, and Derived lipids) 1. **[SIMPLE LIPIDS]** - They are esters of fatty acids with alcohols. - An ester is formed when acid reacts with alcohol. **THERE ARE TWO TYPES OF SIMPLE LIPIDS**: (Fats and Waxes) **FATS** -- Esters of fatty acids with glycerol. ***Structure:*** consist of three molecules of fatty acids esterified with one molecule of glycerol. - All the three fatty acids can be same or different. **Nomenclature of Triglycerides** - The carbon atoms of glycerol of triglycerides are indicated with both Indo-Arabic numbers and Greek alphabets - The triglycerides are further subdivided based on type of fatty acids esterified to glycerol. - **Simple Triglyceride** -- All the three fatty acids esterified to glycerol are same.\ ex: Tripalmitin - **Mixed triglyceride** -- All the three fatty acids esterified to glycerol are different. -Steoric acid and one molecules of palmitic acid.\ ex: : 1,3 disteavro palmitin **OTHER NOTEWORTHY ACYL GLYCEROLS** 1. **Diacylglycerol** -- 2 fatty acids are esterified to glycerol. - 1,2-diacyglycerol and 1,3-diacylglycerol. - In 1,2- diacylglycerol, the 1st and 2nd--OH groups are esterified. 2. **Monoacylglycerol** - **1-monoacylglycerol and 2-monoacylglycerol.\ ** - In 1- monoacylglycerol the 1st ---OH group is esterified. **Functions of Triglycerides** - Storage lipids in animals and in plants. - Fat stored under the skin serve as energy store and as insulator against cold. **Functions of Partial Acylglycerols** - Found in some tissues - Mainly they are formed as intermediates during the synthesis of triglycerides and during digestion of fat. **PHYSICAL PROPERTIES OF TRIGLYCERIDES** - Pure fats have no colour, taste and odor. - At room temperature, fats of plant origin remain oil - Triglycerides containing asymmetric carbon atom are optically active. **CHEMICAL PROPERTIES OF FATS** 1. **Saponification** -- When fats are boiled with bases like KOH or NaOH glycerol and salts of fatty acids are formed. 2. **Hydrogenation** -- It converts unsaturated fatty acids of triglycerides into saturated fatty acids. 3. **Hydrogenation** -- Hardening 4. **Lipid Peroxidation** - **Rancidity-** Fat develops even on prolonged storing. - Atmospheric oxygen reacts with unsaturated fatty acids of triglycerides and forms lipid peroxides. - It is due to formation of lipid peroxides. **WAXES** -- Esters of fatty acids with long chain alcohol. Examples: - **Wool fat**- Lanolin, Lanosterol, Agnosterol. - **Cholesterol ester**- wax **present in the blood** (lipoprotein) and cell membranes. - **Bees wax**- Wax is an ester of palmitic acid with myricyl alcohol. **FUNCTION OF WAXES** - Serve as protective coatings on skin, fur and feathers of animals, birds and on fruit and leaves of plants - Water barrier for animals, birds and insects. Further wax is hard in cold climate and soft in hot climate. - Marine organisms use wax as source of energy. **COMPOUND LIPIDS** - Esters of fatty acids with alcohol containing nitrogenous bases and additional groups. - Compounds lipids are also divided into: - phospholipids - glycolipids. - **Based on alcohol compounds lipids are subdivided into:** 1. **[Glycerophospholipids or Phospholipids\ ]** - They contain two molecules of fatty acids esterified to first and second hydroxyl groups of glycerol. - The third hydroxyl group of glycerol is esterified to phosphoric acid. - Further a nitrogen base or second alcohol is also esterified to phosphoric acid. - Glycerophospholipid without second alcohol is known as phosphatidic acid. - Some glycerophospholipids are named according to second alcohol or nitrogen base and they are considered as derivatives of phosphatidicacid. -Phosphatidyl serine\ -Phosphatidyl inositol 1. **Phosphatidylcholine:** -It contains two fatty acids esterified to first and second hydroxyl group of glycerol. The third hydroxyl is esterified to phosphoric acid to which second alcohol choline is also esterified. - Contains a saturated fatty acid at C-1 position and unsaturated fatty acid at C-2 position. - Major phospholipid of cell membrane. - Also called: Lecithin 2. **Phosphatidyl ethanolamine** \- In which second alcohol ethanolamine is esterified to phosphoric acid of phosphatidic acid.\ -Also called: Cephalins 3. **Phosphatidyl serine** -Amino acid serine is esterified to phosphoric acid of phosphatidic acid. -Also called: amino phospholipids 4. **Phosphatidyl Inositol** -Polyol inositol is esterified to phosphoric acid of phosphatidic acid. \- Cephalins are major component of cell membrane, lipoproteins and nervous tissue.\ \ - involved in signal transduction. **[Other Noteworthy Phospholipids]** **Dipalmitoyl Lecithin** **Structure:** -Two molecules of palmitic acid are esterified to 1st and 2nd carbon atoms of glycerol. - Aphosphocoline is esterified to the third hydroxyl group. It is secreted in alveoli of lungs. - Acts as surfactant in the lungs. - Maintain shape - Medical importance:30 weeks of gestation **Cardiolipin** - It is a double glycerophospholipid. It contains two phosphatidic acids esterified to C and C-3 of glycerol. - It has immunological properties and used in the diagnosis of syphilis. **\ Lysophospholipids** **STRUCTURE:** - They are derivatives of glycerophospholipids. - They contain only one acyl group instead of two acyl groups. - Component of cobra venom and a strong hemolyzing agent. **Plasmalogens\ STRUCTURE:** - They are also glycerol phospholipids. - These compounds contain unsaturated fatty alcohol in place of fatty acid at the C-1position. - Hence, the normal ester linkage is replaced by ether linkage on the C-1 carbon of glycerol. - Usually nitrogen bases are choline, serine and ethanolamine - Content is more in cancer cells. 2. Sphingo lipids -- They contain fatty acid long chain amino alcohol sphingosine and bases or additional groups. They are subdivided into: ***Sphingomyelins and Glycolipids*** **SPHINGOMYELINS** -- Fatty acid is linked to sphingosine by an amide bond and phosphorylcholine is esterified toC-1 hydroxyl of sphingosine. - They are simple and most abundant sphingolipids. They are present in most of animal membranes. - Myelin sheath of nerve cells is rich in sphingomyelins. - Grey matter also contain sphingomyelins **GLYCOLIPIDS** - They are subdivided into: Cerebrosides and Gangliosides - [Cerebrosides] -- Contain sphingosine, fatty acid and sugar. - The combination of sphingosine and fatty acid is called as ceramide. - Cerebrosides differ in the type of sugar, usually they are named according to the sugar present. - In some cerebrosides, sulfate is attached to sugar then they are called assulfatides or sulfolipid. - Cerebrosides occur in large amounts in white matter of brain and in myelins heath of nerves. - Some cerebrosides are present in non-neural tissue. - **[Galacto cerebroside]**- common sugar, if the sugar is galactose it is galacto cerebroside. - **[Gluco cerebroside-]** if the sugar is glucose it is gluco cerebroside. **GANGLIOSIDES** -- Highly complex sphingolipids. Function: - They contain ceramide, oligosaccharide and sialic acid. - They are abundant in grey matter of brain. They are also found in non-nerval tissues. - They are components of hormone receptors. - They also function as receptors for toxins of cholera, influenza and tetanus. - They are also involved in cell-cell recognition, growth, differentiation and carcinogenesis. **DERIVED LIPIDS - FATTY ACIDS** -- They are acids derived from fats steroids, glycerol and retinol. - They are monocarboxylic acids containing long hydro carbon side chain. - Based on the nature of hydrocarbon side chain, they are divided into: - **[Saturated fatty acids]** -Single bond - **[Unsaturated fatty acids]** -\ - One or more double bond\ - Monounsaturated or Polyunsaturated - Fatty acids are also divided based on hydrocarbon chain length. They are: - [Short chain fatty acids] -6 Carbon atoms - Medium chain fatty acids\ -6-12 carbon atoms - Long chain fatty acids\ -13-20 carbon atoms - Very long chain fatty acids\ -22-30 carbon atoms **Cis-trans isomerism** -- Unsaturated fatty acids exhibit cis-trans isomerism. - In the cis-isomer bulky groups are located on the same side of doublebond where as in trans isomer they are on the opposite side of double bond. - Cis and trans isomers are not interchangeable in cells. Only cis isomerscan fit into cell membrane because of bend at double bond. **Nomenclature of Fatty Acids** - **[Saturated fatty acids]** - Have both trivial names and systematic names - Systematic name Consist of two parts: - Name of hydrocarbon chain forms first part. 'oic' substituted in place of 'e' of hydrocarbon name forms second part. - Usually saturated fatty acids end as anoic acids. **Nomenclature of Fatty Acids** - **[Unsaturated fatty acids\ ]** - Trivial names, systematic names, -end names and shorthand forms. - Systematic name - The name of hydrocarbon forms first part of systematic name of unsaturated fattyacids. But 'enoic' substituted in place of 'ne' of name of hydrocarbon forms secondpart. Number of double bonds are written before 'enoic' and symbol showingposition of double bonds and isomerism around double bond are written betweentwo parts or in the beginning. Example: Mono unsaturated fatty acid palmitoleic acid (trivial name) containing 16 carbon atomand one double bond between 9 and 10 carbon atoms (Hexa t d r e m cane + Δ9-cis-mono+enoic+acid) ---→ cis-9-Hexadecaenoic acid. **ESSENTIAL FATTY ACIDS** - Not synthesized in the body. - **PUFA**- Poly unsaturated fatty\ acid. - They are linoleic acid (LA), linolenic acid (LNA) and arachidonic acid (AA). - **[Nutritionally important:]** Omega-3 and Omega-6 fatty acids - [Linolenic acid (LNA)] -- Omega - [Linoleic acid] ( LA)-- Omega-6 - [Omega 6] -- Redness skin, Liver abnormality. - They are essential for the synthesis of eicosanoids. - They are also required for membrane lipids. **STEROIDS** -- Complex molecules containing four fused rings. - The four fused rings make up 'cyclopentanoperhydrophenanthrene' steroid nucleus. - Most abundant steroids are sterols which are steroid alcohols.\. - Steroids are called as non-saponifiable lipids because they contain no fatty acidsand they can not form soaps. **CHOLESTEROL** -- In animal tissue, cholesterol is the major sterol. - 3-hydroxy-5 - 6-cholestene - Found in bile - Important components of cell membrane and lipoproteins. - In a normal 65 Kg adult, 200 gm of cholesterol is present. - Steroids with diverse physiological functions are derived from cholesterol. - **Vitamin D** - **Bile Acids** - Steroids with diverse physiological functions are derived from cholesterol. - **Hormones of adrenal cortex\ **-cortisol, corticosterone and aldosterone. - **Female sex hormones**\ -Progesterone and estrogen - **Male sex hormones\ **-Testosterone and androsterone **Other Noteworthy Steroids** - **Ergosterol** -- Provitamin of vitamin D found in yeast and plants. - **Sitosterol** -- Present in plants. - **Cardiac glycosides** -- like ouabain and streptomycin an antibiotic. - **Coprostanol** -- found in feces is derived from cholesterol. - **Wool fat sterols** -- like agnosterol and lanosterol. **CLASSIFICATION OF LIPIDS -ACCORDING TO THEIR INTERACTION WITH WATER (Polar and Non-Polar)\ ** - **Polar lipids --** They are further sub-divided into 3 sub-classes: - [Class one] polar lipids Non-swelling water insoluble amphipathic molecules (Amphiphiles) which forms thin lipid monolayer in water. - [Class two] polar lipids swelling and water insoluble amphiphiles which forms stable lipid monolayer as well as laminated lipid water structure known as liquid crystals. - [Class three] polar lipids Water soluble amphiphiles, which contain strong polar head groups. These are water soluble only at low concentrations. - Non-polar Lipids - Insoluble in water - Cholesterol esters, carotenes and hydrocarbons **EICOSANOIDS** - Derived from eicosapolyenoic fatty acid like arachidonic acid. - They are prostanoids, leukotrines (LTA) and lipoxins (LX). - The prostanoids include prostaglandins (PG), prostacyclins (PGI) and thromboxane's (TXA). - Often word prostaglandins is used to indicate all prostanoids. - Prostaglandins - Chemically prostaglandins are derivatives of a 20 carbon prostanoic acid. - Prostanoic acid is a cyclic compound with two side chains. - The cyclic ring present in prostanoic acid is a cyclopentane ring. - There are some six or more types of prostaglandins. - They differ in the substituents on the cyclopentane ring. - Prostacylins - Contain a second five-numbered ring in addition to the one common to all prostaglandins. - Thromboxane - Identified first in thrombocytes - Contain a six numbered heterocyclic oxane ring. - Leukotriens and Lipoxins - Found in leukocytes - They are derivatives of arachidonic acid and contain no cyclic ring. - Function as local hormones. - They act on several organs and produce physiological as well as pharmacological effects. LIPOPROTEINS - Lipid protein complexes found in plasma. - They are non-covalent assemblies The protein part of lipoprotein is called as apolipoprotein or apoprotein. - Structure consist of non-polar lipid core surrounded by apoproteins and more polar lipids - Chylomicrons - Very low density liporoteins - Low density liporoteins - High density lipoproteins - a-lipoproteins - pre-B-lipoproteins - B-lipoproteins c - Chylomicrons Composition of Lipoproteins - Lipids of lipoproteins - Lipid constituents of lipoproteins are mostly triglycerides, free and esterified cholesterol and phospholipids. - The proportion of triglycerides, cholesterol and phospholipids differs in various lipoproteins. Apoproteins of lipoproteins - The proportion of protein part differs in various lipoproteins. - The composition of apoprotein part also differs among various lipoproteins. - There are five types of apoproteins. - Some of the apoproteins have subtypes. - Apo-B -- It is a glycoprotein contains sialic acid, mannose, glucose, galactose and fructose. - Other little known apoproteins are apo F, apo G and apo H. Functions of Lipoproteins - Involved in the transportation of lipids in the body. - Other Noteworthy Functions of Lipoproteins - Important for synthesis and degradation of lipoproteins - Activators/inhibitors of some enzymes associated with lipid metabolism. Lipoprotein X (LpX) -- It is a variant of LDL. - Bilammallar vesicle with an aqueous lumen. - It contains equal amounts ophospholipids and cholesterol. - Triglycerides and cholesterol esters are present in onlysmall amounts - Appears in the plasma of cholestatic patients. It may be formed in bile and entersplasma due to regurgitation that occurs in cholestatic individuals.