LIPIDS Lecture 1

Overview- Definition Lipids are organic compounds composed of alcohol and fatty acids (FA) combined together by ester linkage. An ester linkage is a functional group of the formula: Lipids are mostly hydrophobic (insoluble in water) but soluble in nonpolar organic solvents such as chloroform, benzene, and ether. Fats are stored in adipose tissue.

Functions of lipids: Storage for energy (25% of body needs). Structural components of cell membrane and nervous system. Precursor of many fat soluble vitamins (A, D, E, and K) and hormones. Lipoprotein help in transporting proteins. Acts as electric insulators in neurons. A subcutaneous thermal insulator against loss of body heat. Supply the essential fatty acids that can not be synthesized by the body.

Fatty Alcohol Fatty acids

The principal classes of storage and membrane lipids: All of the classes shown here have either glycerol or sphingosine as the backbone Sphingo-phospho-lipid Sphingo-glyco-lipid

I. Fatty Alcohols Sphingosine Glycerol A trihydric alcohol (contains three OH groups). Has a popular name (glycerine). It has the ability to form esters with fatty acids (next slide for details). It is the major backbone of storage lipid (Triglycerols), it can also present in the structure of phospholipids (Glycero-phosphor-lipid). It is synthesized in the body from glucose. It has a nutritional value by converting to glucose .  Amino alcohol with an unsaturated hydrocarbon chain. Found especially in nervous tissue and cell membranes. It is a part of the family of Sphingolipids (sphingoglycolipid & sphingo-phospholipids). It is synthesized in the body from serine and palmitic acid.

Esterification reactions of Glycerol 1 Glycerol molecule has 3- OH groups: According to the number of the OH- groups which participate in ester linkage formation with Fatty acids >>> different kind of lipids can be formed.

Esterification reactions of Glycerol Monoglycerides (monoacylglycerols): are a class of glycerides which are composed of a molecule of glycerol linked to 1 fatty acid via an ester bond. Diglycerides (diacylglycerol:DAG), a class of glycerides which are composed of a molecule of glycerol linked to 2 fatty acid via an ester bond. Triglycerides TG (triacylglycerol, TAG, or triacylglyceride): a class of glycerides which are composed of a molecule of glycerol linked to 3 fatty acid via an ester bond.

Esterification reactions of Sphingosine Sphingosine presents in 2 membrane “structural” lipids: Sphingolipids = sphingoglycolipid & sphingophospholipids. In Both; sphingoglycolipid & sphingophospholipids.: the amino group of sphingosine is linked to FAs by an amide bond. In sphingophospholipid: the primary hydroxyl group of sphingosine is esterified to phshoryl-choline, producing sphingomyelin (the only significant sphingophospholipid in human) In sphingoglycolipids, one or more sugar residues joined in a β-glycosidic linkage at the 1-hydroxyl position . Sphingoglycolipids β-glycosidic bond Amide bond Phosphoryl-choline

II. Fatty acids OVERVIEW Fatty acids consist of a hydrophobic hydrocarbon chain with a terminal carboxyl group. They exist either free in the body (unestrified ), or as fatty acyl esters in more complex molecules, such as triglycerides (triacylglycerols). This esterified form of fatty acids is stored in adipose tissue, serve as the major energy of the body.

Fatty acids classifications: One system of fatty acid classification is based on the number of double bonds. Fatty acids with no double bond known as SATURATED fatty acids Fatty acids with one or more double bonds known as UNSATURATED fatty acids

Fatty acids classifications: A. Saturated fatty acids (FA): Have no double bonds with 2-25 carbons. Short chains are usually solid at room temperature The carbon chain can have either even or odd number. General molecular formula:

Fatty acids classifications: A. Saturated fatty acids (FA): They can be divided according to the length of the hydrocarbon chain: Short chain Saturated FA (SCSFAs) Medium chain Saturated FA (MCSFAs): Long Chain Saturated FA (LCSFAs)

Short chain Saturated FA (SCSFAs) Medium chain Saturated FA (MCSFAs) Long chain Saturated FA (LCSFAs) contain 2-5 carbons. They are mainly produced during fermentation of the soluble dietary fiber by beneficial large intestinal bacteria. They include: Acetic acid (2:0) Propionic acid (3:0) Butyric acid (4:0) contain 6–12 carbons. Due to their shorter chain length, medium-chain triglycerides are more rapidly broken down and absorbed into the body. caproic acid (C6:0) capric acid (C10:0) lauric acid (C12:0). Whole food sources of MCSFA include coconut oil, palm kernel oil and dairy products. Contain more than 12 carbons. palmitic acid (16:0) stearic acid (18:0) It is found almost exclusively in animal fats such butter and ghee and in hydrogenated oils.

Fatty acids classifications: B. Unsaturated fatty acids (FA): Have one or more double bonds They can be divided according to the number of the double bonds presence: Monounsaturated fatty acids: contain one double bonds Polyunsaturated fatty acids: contain more than one double bonds

B. Unsaturated fatty acids (FA): Monounsaturated fatty acids: contain one double bonds Palmitoleic acid: It is found in all fats It is C16:1Δ9 >> “16 carbons, one double bond located at carbon #9”

B. Unsaturated fatty acids (FA): Monounsaturated fatty acids: contain one double bonds ii. Oleic acid: It is the most common fatty acid in natural fats It is C18:1Δ9 >> “18 carbons, one double bond located at carbon #9”

B. Unsaturated fatty acids (FA): 2) Polyunsaturated fatty acids: contain more than one double bonds This class includes many important compounds, such as essential fatty acids Essential Polyunsaturated fatty acids are that can not be synthesized by the human body and must be taken in adequate amounts in the diet. They are required for normal growth and metabolism.

B. Unsaturated fatty acids (FA): 2) Polyunsaturated fatty acids: contain more than one double bonds Linoleic acid: It is the most important since it is an important precursor for other essential fatty acids in the body. found in vegetable oils, nuts, seeds and animal products It is C18:2Δ9,12 >> “18 carbons, two double bonds located at carbon #9 and # 12” Linoleic acid is also known as a polyunsaturated omega (ω)-6 fatty acid >>18:2(ω-6). Omega-6 fatty acids are polyunsaturated FAs with a double bond (C=C) at the sixth carbon atom from the end of the carbon chain (methyl end)

B. Unsaturated fatty acids (FA): 2) Polyunsaturated fatty acids: contain more than one double bonds ii. Linolenic acid: It is also a precursor for other essential fatty acids in the body, therefore it is very important. found in flaxseed, canola oil, soybean and soybean oil, walnut and walnut oil.. It is C18:3Δ9,12,15 >> “18 carbons, three double bonds located at carbon #9, # 12 and # 15” Linolenic acid is also known as a polyunsaturated omega (ω)-3 fatty acid>>18:3(ω-3). Omega-3 fatty acids are polyunsaturated FAs with a double bond (C=C) at the third carbon atom from the end of the carbon chain

B. Unsaturated fatty acids (FA): 2) Polyunsaturated fatty acids: contain more than one double bonds iii. Arachidonic acid: It is an important component of phospholipids of membranes of the body's cells, and is abundant in the brain, muscles, and liver. Arachidonic acid is not one of the essential fatty acids. However, it does become essential if there is a deficiency in linoleic acid or if there is an inability to convert linoleic acid to arachidonic acid. Therefore it is polyunsaturated omega-6 fatty acid 20:4(ω-6). It is C20:4Δ5,8,11,14 >> “18 carbons, four double bonds located at carbon #5, #8,# 11 and # 14”