Lipids PDF

With water, I say, “ touch me not”; To the tongue, I am tasteful; Lipids Within limits, I am dutiful In excess I am dangerous Lipids are a loosely...

With water, I say, “ touch me not”; To the tongue, I am tasteful; Lipids Within limits, I am dutiful In excess I am dangerous Lipids are a loosely defined, diverse group of organic molecules with one main characteristic: they are insoluble in water. The most familiar lipids are fats and oils. Lipids have a very high proportion of nonpolar carbon-hydrogen (C—H) bonds So long-chain lipids cannot fold up like a protein to sequester their nonpolar portions away from the surrounding aqueous environment  Lipids Instead, when placed in water many lipid molecules will spontaneously cluster together and expose what polar groups they have to the surrounding water while sequestering the nonpolar parts of the molecules together within the cluster. This spontaneous assembly of lipids is of paramount importance to cells, as it underlies the structure of cellular membranes Lipids are not polymers Mostly small molecules  Classification of Lipids Lipids Simple Complex Ester of FA +alcohol FA+ alcohol + groups Derived (Phosphate, nitrogenousDerivatives obtained from base, carbohydrates, hydrolysis of simple and Miscellaneous Fats & oil/ proteins Triacylglycerol Waxes complex lipids. Compound Neutral possessing the FA + FA + other Ex: Cholesterol, bile acids, characteristic of Lipids and adrenocortical glycerol alcohol than hormones lipids. Uncharged lipids glycerol Ex: carotenoids, Ex: mono, di- Glycolipids Lipoprotein Other hydrocarbon and triacylglycerol, Phospholipids Lipids with FA+ Aminolipids Cholesterol FA + alcohol + protein Contain carbohydrates Lipopolysaccharides Glycerol phosphate Ex: Sphingosine –alcohol Lecithin, Glycerophospholipid Sphingophospholipids cephalin Ex: Sphingomyelin  Functions of Lipids Concentrated fuel reserves of the body (Triacyl glycerol) Constituent of membrane Serves as a source of structure fat-soluble vitamins Regulate the membrane (A, D, E, and K) permeability (Phospholipids) Protects the internal organs, Cellular metabolic serves as insulating materials & regulator give shape and smooth (steroid hormones appearance to the body and prostaglandins)  Fatty acids (FA) Fatty acids are carboxylic acids with a hydrocarbon side chain. They are the simplest form of lipids Fatty acids mainly occur in the esterified form as major constituents of various lipids. They are also present as free (unesterified) FA. Fatty acids of animal origin are much simpler in structure in contrast to those of plant origin Most of the FA are of even carbon (14-20 C) E.g. Palmitic acid, stearic acid Well-known odd chain FA are propionic acid and valeric acid  Classification of Fatty acids Contain one or more double bonds Not contain double bonds Trans fatty acids (TFAs) are unsaturated fatty acids that contain at least one nonconjugated double bond in the trans-configuration, resulting in a straighter shape. Most commercially prepared foods contain TFAs. Classification of Fatty acids Trans Fat  Nomenclature of Fatty acids Systematic name Common name The naming of a fatty acid is based on More widely used the hydrocarbon from which it is derived. The saturated fatty acids end with a suffix –anoic. E.g., octanoic acid. The unsaturated fatty acids end with a suffix –enoic. E.g. octadecenoic acid  Nomenclature of Fatty acids Delta Nomenclature For delta nomenclature you need to know 3 things: 1. Number of carbons in the fatty acid 2. Number of double bonds 3. Number of carbons from the carboxylic acid (alpha) end to the first carbon in the double bond(s) Number of carbons in the fatty acid = 18 Number of double bonds = 1 Number of carbons from the carboxylic acid end to the first carbon in the double bond = 9 Δ9 - double bond is between 9 and 10 c of the fatty acids  Nomenclature of Fatty acids Omega nomenclature Is almost exactly the same as the delta nomenclature, the only differences being: Carbons are counted from the methyl (omega) end instead of the carboxylic acid end The omega symbol is used instead of the delta symbol For omega nomenclature you need to know 3 things: 1. Number of carbons in the fatty acid 2. Number of double bonds 3. Number of carbons from the methyl end (Omega end) to the first carbon in the double bond closest to ω-9 double bond the methyl end position (9 and 10) from the ω end  Nomenclature of Fatty acids Number of carbons in the fatty acid = 18 Number of double bonds = 1 Number of carbons from the methyl (aka omega) end to the first carbon in the double bond closest to the methyl end = 9 If it is a saturated fatty acid, then the omega nomenclature is not added to the end of the name. If it is an 18-carbon saturated fatty acid, then it would be named 18:0.  Nomenclature of Fatty acids Total number of carbon atoms Number of double bond Position of the double bond starting from carboxyl end  Essential Fatty acids Essential Fatty acids; The fatty acids that cannot be synthesized by the body and, therefore, should be supplied in the diet There are two families of EFA, omega-3 (ω-3) and omega-6 (ω-6). Omega-3 fatty acids have carbon double bond in the ω-3 position (the third bond from the methyl end of the fatty acid) ω-6 fatty acids have it in the ω-6 position (the sixth bond from the methyl end of the fatty acid) They are polyunsaturated fatty acids (PUFAs) Why the human body not synthesize these FA?  Functions of Fatty acids Required for- - Membrane structure and function - Formation of lipoprotein - Transport of cholesterol - Prevention of fatty liver - Synthesis of eicosanoids  Triacylglycerol (TAG) Formerly called triglycerides TAGs are insoluble in water, non-polar in character, and commonly known as neutral fat Most abundant group of lipids. Primarily functions as fuel reserves of animals (men 20%, women 25% by weight) which is sufficient to meet the body’s caloric requirements for 2-3 months The fats and oils widely distributed in both plants and animals are chemically TAGs.  Triacylglycerol (TAG) TAG Simple Mixed Same type of FA residue at all the three 2-3 different type of FA Monoacyl carbon E.g. Tristearin E.g. Palmitoyl 2-linoleoyl glycerol glycerol Diacyl glycerol TAGs of plant, in general, have Triacyl glycerol higher content of unsaturated FA compared to that TAG are esters of glycerol with fatty acids animal  Properties of TAG 1. Hydrolysis TAG undergo stepwise enzymatic hydrolysis to finally liberate free FA and glycerol, catalyzed by lipase Important for digestion of fat in GI tract and fat mobilization from adipose tissue  Properties of TAG 2. Saponification The hydrolysis of TAG by alkali to produce glycerol and soaps is known as saponification  Properties of TAG 3. Rancidity The term used to represent the deterioration of fats and oils resulting in an unpleasant taste and are unsuitable for consumption Fats containing unsaturated FA are more susceptible to rancidity Occurs when fats and oils are exposed to air, moisture, light bacteria etc. Hydrolytic rancidity occurs due to partial hydrolysis of TAG by bacteria Oxidative rancidity – due to oxidation of unsaturated FA , results in the formation of a dicarboxylic acid, aldehyde, and ketone Antioxidants can be used to prevent the occurrence of oxidative rancidity  Properties of TAG 4. Lipid peroxidation in vivo: In living cells, TAGs undergo oxidation to produce peroxidase and free radicals which can damage the tissue. The free radicals are believed to cause inflammatory disease, aging, cancer, atherosclerosis  Phospholipids Compound or complex lipids containing phosphoric acid, in addition to FA, and alcohol Phospholipases are the group of the enzyme that hydrolyze phospholipids Two types 1. Glycerophospholipids 2. Sphingophospholipids  Phospholipids 1. Glycerophospholipid Major lipids found in cell membrane They consist of glycerol 3-phosphate esterified at its C1 Usually, C1 contains saturated FA and C2 contains unsaturated FA E.g. Phosphatidic acid, Lecithin, Cephalins, Phosphatidylinositol Phospholipids 2. Sphingophospholipids Sphingophospholipids contain a sphingosine backbone, a fatty acid chain, a phosphate group, and a polar head group. They are formed from the amino alcohol sphingosine, to which a fatty acid is attached, creating ceramide. A phosphate group and a polar head group are then added to ceramide.  Functions of Phospholipids ✓ In association with proteins, phospholipids form the structural components of membranes and regulate membrane permeability ✓ Phospholipids (lecithin, cephalin and cardiolipin) in the mitochondria are responsible for maintaining the conformation of electron transport chain components, and thus cellular respiration. ✓ Phospholipids participate in the absorption of fat from the intestine. ✓ Phospholipids are essential for the synthesis of different lipoproteins, and thus participate in the transport of lipids. ✓ Accumulation of fat in liver (fatty liver) can be prevented by phospholipids, hence they are regarded as lipotropic factors. ✓ Phospholipids participate in the reverse cholesterol transport and thus help in the removal of cholesterol from the body. ✓ Phospholipids act as surfactants (agents lowering surface tension).  Glycolipids Important constituents of the cell membrane and nervous tissues (particularly the brain) Cerebrosides are the simplest form of glycolipids.  Lipoproteins Lipoproteins are molecular complexes of lipids with proteins. They are the transport vehicles for lipids in the circulation. There are five types of lipoproteins, namely - Chylomicrons - Very low-density lipoproteins (VLDL) - Low-density lipoproteins (LDL) - High-density Iipoproteins (HDL) - Free fatty acid-albumin complexes  Steroids Steroid, any of a class of natural or synthetic organic compounds characterized by a molecular structure of 17 carbon atoms arranged in four rings. Steroids can be broadly categorized into different groups based on their functions Cholesterol: It's a type of steroid that's crucial for the structure of cell membranes. It's also a precursor for the synthesis of other steroids like steroid hormones.  Steroids Steroid Hormones These are hormones that act as chemical messengers in the body, regulating various physiological processes. Ex: Sex Hormones: Estrogen, progesterone, and testosterone, Corticosteroids: Glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone) that regulate metabolism, immune response, and electrolyte balance.  Steroids Vitamins Some vitamins are derived from steroids. For instance, vitamin D is a steroid derivative crucial for calcium absorption and bone health. Anabolic Steroids Synthetic compounds related to testosterone that can have muscle-building (anabolic) effects. They are sometimes misused for performance enhancement, but their use can have adverse health effects  Waxes A wax is a simple lipid, an ester of a long-chain alcohol and a fatty acid. The formation of waxes occurs through the condensation reaction between a long-chain alcohol and a fatty acid. This ester linkage between the alcohol and the fatty acid creates the structure of a wax. The alcohol may contain from 12-32 carbon atoms. They include higher alkanes and lipids, typically with melting points above about 40 °C  Waxes Waxes have various functions in organisms and the environment. They serve as protective coatings in plants, animals, and insects, helping to prevent water loss, repel water, reduce evaporation, and protect against damage from external factors like UV radiation or pathogens. In some organisms, waxes are also involved in structural support and insulation. For example, in plants, the waxy coating on leaves and fruits helps prevent water loss and acts as a barrier against pests. In animals, waxes contribute to the formation of protective coatings on feathers, fur, or skin, providing insulation and waterproofing. Waxes  Amphipathic Lipids Molecules that contain both hydrophobic and hydrophilic groups are known as amphipathic Among the lipids, fatty acids, phospholipids, sphingolipids, bile salts and cholesterol (to some extent) are amphipathic in nature.  Lipids https://youtu.be/5BBYBRWzsLA Thank You!!