Lipids PDF

LIPIDS What are lipids? It is an organic compound found in living organisms that is insoluble in water. Soluble in alcohol, ether, and chloroform. Lipids are an important component of living cells. Lipids are easily stored in the body. Serves as source of fuel.  The structural diversity that...

LIPIDS What are lipids? It is an organic compound found in living organisms that is insoluble in water. Soluble in alcohol, ether, and chloroform. Lipids are an important component of living cells. Lipids are easily stored in the body. Serves as source of fuel.  The structural diversity that is associated with lipid molecules: Some are esters, amides, alcohols Some are acyclic, cyclic, polycyclic. The common thread that ties all of the compounds of together is solubility rather than structure. All are insoluble in water. Group of Lipid Molecules Group of Lipid Molecules Fats and oils Waxes Phospholipids Sterols (cholesterol) Five categories on the basis of lipid function: 1. Energy-storage lipids (triacylglycerols) 2. Membrane lipids (phospholipids, sphingoglycolipids, and cholesterol) 3. Emulsification lipids (bile acids) 4. Messenger lipids (steroid hormones and eicosanoids) 5. Protective-coating lipids (biological waxes) ▪Triacylglycerol – energy-storage lipid (LT) Function within the body as energy-storage materials. Concentrated primarily in special cells (adipocytes). Triacylglycerols are much more efficient at storing energy than is glycogen. These energy-storage lipids are the most abundant type of lipid present in the human body.  In terms of functional groups present, triacylglycerols are triesters. Fatty acids are the carboxylic acids involved in triacylglycerol formation. Simple and complex triacylglycerol  FATS & OILS Both are complex mixtures of triacylglycerol molecules. FATS OILS a triacylglycerol mixture that is a solid or a a triacylglycerol mixture that is a liquid at room semi-solid at room temperature (25C). temperature (25C). Generally, obtained from animal sources. Generally, obtained from plant sources (although Saturated fatty acids predominate. there are also fish oils). Larger amounts of mono- and polyunsaturated fatty acids. Pure fats and pure oils are colorless, odorless, and tasteless. The tastes, odors, and colors associated with dietary plant oils are caused by small amounts of other naturally occurring substances present in the plant that have been carried along during processing. CELL MEMBRANES It is a lipid-based structure that: Separate a cell’s aqueous-based interior from the aqueous environment surrounding the cell. Controls the movement of substances into and out of the cell. General types of membrane proteins: Integral membrane protein – a membrane protein that penetrates the cell membrane. Peripheral membrane protein – a non-penetrating membrane protein located on the surface of the cell membrane. Transport across cell membranes Membrane Lipids  LIPOPROTEINS – protein carrier system used for distribution. It is a combination of cholesterol and protein. LDL – low density lipoproteins. Bad cholesterol (from the liver to the tissues) HDL – high density lipoproteins. Good cholesterol (excess from tissues to liver) BLOOD CHOLESTEROL – much LDL is transported. Emulsifier : substance that can disperse and stabilize water-insoluble substances as colloidal particles in an aqueous solution. As emulsifying agent it facilitate in the absorption of dietary lipids in the intestine. Approximately 1/3 of the daily production of cholesterol by the liver is converted to bile acids. Bile – a fluid containing emulsifying agents that is secreted by the liver, stored in the gall bladder and released into the small intestine during digestion. Examples of bile acids: Role of Bile Acids in Cholesterol Metabolism Hepatic synthesis of bile acids accounts for the majority of cholesterol breakdown in the body. In humans, 500 mg of cholesterol are converted to bile acids and eliminated in bile everyday. This route for elimination of excess cholesterol is probably important in all animals, but particularly in situations of massive cholesterol ingestion. Excretion of bilirubin and biliverdin via Bile. SEX HORMONES Estrogens – female sex hormones. Synthesized in the ovaries and adrenal cortex. Responsible for the development of female secondary sex characteristics at the onset of puberty and for regulation of menstrual cycle. Stimulate the development of the mammary glands during pregnancy and induced estrus (heat) in animals. SEX HORMONES Androgens – male sex hormones. Synthesized in the testes and adrenal cortex. Promote the development of secondary male characteristics. Promote muscle growth. SEX HORMONES Progestins – pregnancy hormones synthesized in the ovaries and the placenta. It can: prepare the lining of the uterus for implantation of the fertilized ovum, or suppress ovulation. Natural Hormones and Synthetic Steroids  Wax covers the feathers of some aquatic birds and the leaf surfaces of some plants. Waxes are made up of long fatty acid chains esterified to long-chain alcohols. Biological waxes are esters of long-chain (C14 to C36) saturated and unsaturated fatty acids with long-chain (C16 to C30) alcohols. Biological waxes find a variety of applications in the pharmaceutical, cosmetic, and other industries. FATTY ACIDS Fatty acids, both free and as part of complex lipids play a number of key roles in metabolism 1. Major metabolic fuel 2. Storage and transport of energy 3. As essential components of all membranes 4. Gene regulators  What are fatty acids? Fatty acids are structural components of all the lipids except cholesterol, bile acids, and steroid hormones. Unbranched long chain of naturally occurring monocarboxylic acid. Typically 12-18 carbon atoms. Structure of fatty acids Fatty acids are synthesized from linear acetogenins of acetate pathway. Fatty acids are carbon chains with a methyl group at one end of the molecule (designated omega, ω) and a carboxyl group at the other end. The carbon atom next to the carboxyl group is called the α carbon, and the subsequent one the β carbon. Structure of fatty acids The systematic nomenclature for fatty acids may also indicate the location of double bonds with references to the carboxyl group (∆). Fatty acids may be named according to systematic or trivial nomenclature. One systematic way to describe fatty acids are related to the methyl (ω) end. This is used to describe the position of double bonds from the end of the fatty acid. Chain Length In terms of carbon chain length, fatty acids are characterized as: long-chain fatty acids (C19 onward), medium chain fatty acids (C13 and C18), or short-chain fatty acids (C1 and C12). Fatty acids are rarely found free in nature but rather occur as part of the structure of more complex lipid molecules. Physical Properties of Fatty Acids Water Solubility – is a direct function of carbon chain length. Solubility decreases as carbon chain length increases. Short chain – slight solubility in water Long chain – essentially insoluble in water. Melting Points – are strongly influenced by both carbon chain length and degree of unsaturation. As carbon chain increases, melting point increases. With the same number of carbon atoms saturated fatty acids have higher melting points than unsaturated fatty acids. The greater the degree of unsaturation, the greater the reduction in melting points. Degree of Saturation and Melting Decreasing melting point, increasing degree of unsaturation due to decreased molecular attraction between carbon chains. The double bonds in unsaturated FA, generally have the cis configuration produce “bends” in the chain. These “bends” prevent unsaturated FA from packing together as tightly as saturated FA. Classification of Fatty Acids Fatty acids are classified according to the number of carbon atoms and presence or absence of double bond, etc. 1. Saturated acids 2. Unsaturated acids 3. Branched chain acids 4. Cyclic acids 5. Hydroxy & keto-derivatives  Classification of Fatty Acids The terms saturated, mono- unsaturated, and poly-unsaturated re fer to the number of hydrogens attached to the hydrocarbon tails of the fatty acids as compared to the number of double bonds between carbon atoms in the tail.  The fatty acids present in naturally occurring lipids almost always have the following three characteristics: 1. An unbranched carbon chain 2. An even number of carbon atoms in the carbon chain 3. Double bonds, when present in the carbon chain, in a cis configuration Saturated Fatty Acids Monounsaturated Fatty Acids Unsaturated Fatty Acids and Double-bond Position A numerically based shorthand system exists for specifying key structural parameters for fatty acids. In this system, two numbers separated by a colon are used to specify the number of carbon atoms and the number of carbon–carbon double bonds present.  To specify double-bond positioning within the carbon chain of an unsaturated fatty acid, the preceding notation is expanded by adding the Greek capital letter delta (Δ) followed by one or more superscript numbers. The notation 18:3(Δ9,12,15) denotes a C18 PUFA with three double bonds at locations between carbons 9 and 10, 12 and 13, and 15 and 16. Polyunsaturated “essential fatty acids” (EFAs)  The human body needs them for many functions, from building healthy cells to maintaining brain and nerve function. Omega-3 comes primarily from fatty fish such as salmon, mackerel, and tuna, as well as from walnuts and flaxseed in lesser amounts. Omega-6 mostly comes as linoleic acid from plant oils such as corn oil, soybean oil, and sunflower oil, as well as from nuts and seeds.