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 Lipids are complex molecules composed of carbon, hydrogen, and oxygen.  Lipids are insoluble in water and soluble in nonpolar solvents.  Most lipids are non-polar and are hydrophobic because they contain hydrocarbon chains.

A.The Functions of Fat in the Body: 1.Energy source esp. for muscles. 2.Serves as an energy reserve. Lipid (TGL) Droplets In Adipose tissue

3. Structural components 3. Cell Membrane Structural components Cushion the vital organs to protect them from shock.

5. Thermal Insulator : Subcutaneous layer of fat reduces heat loss in cold weather (helps maintain body temperature).

B. The Functions of Fat in Food: 1.Provide calories (9 kcal per gram). 2.Provide satiety. Lipid-soluble vitamins (A,D,E, and K) 3.Carry Lipid-soluble vitamins (A,D,E, and K) & essential fatty acids. 4.Contribute aroma & flavor.

Humans can grow more fat cells, but can never get rid of them!! As we gain and lose weight, they just swell and shrink. …Makes you think twice about those French fries!!!

Makes you fat! Heart disease, high blood pressure, cancer.

 Are long-chain monocarboxylic acids.  Generally contain an even number of carbon atoms.  General formula is CH3 (CH2)n COOH.

Length of the Carbon Chain – Long-chain, medium-chain, short-chain Degree of Unsaturation – Saturated, Unsaturated (Mono, Poly) Location of Double Bonds – Omega-3 Fatty Acid, Omega-6 Fatty Acid

The Length of the Carbon Chain Short-chain Fatty Acid (l (less than 6 carbons) s than Medium-chain Fatty Acid (6-10 carbons) Long-chain Fatty Acid (12 or more carbons)

“full”, Saturation means “full”, so what could they be full of? H Full of H atoms! And wherever there is a chemical bond, there is stored energy.

CH3 (CH2)n COOH.  General Formula: CH3 (CH2)n COOH.  Each C being “saturated” with H. C–C  Contain only single C–C bonds.  long, straight chain.

 Closely packed.  Strong attractions between chains.  High melting points.  Solids at room temperature.

 Animal foods such as meat, poultry and full-fat dairy products.  Tropical oils such as palm and coconut.

Contributes to cardiovascular disease.

C=C  Contain one or more double C=C bonds.  The kinks made by double bonded C prevent the molecules from packing tightly together.  Few interactions between chains.

 Low melting points  Liquids at room temperature  Plant & fish fats  Vegetable oils

saturatedunsaturated

1.Monounsaturated FA 2.Polyunsaturated FA 3.Eicosanoids

Fatty Acids 1. Monounsaturated Fatty Acids (MUFA) Containing one double bond. Oleic (most common FA)18:1;9

Fatty Acids 2. Polyunsaturated Fatty Acids (PUFA) Containing two or more double bonds Linoleic (corn, peanut, cottonseed)18:2;9,12

– Are identified by position of the double bond nearest the methyl end (CH 3 ) of the carbon chain; this is described as an omega number. – If PUFA has first double bond 3 carbons away from the methyl end = omega 3 FA – 6 carbons from methyl end = omega 6 FA

25 ω 3, ω 6, ω 9 Fatty Acids

Cis-Fatty Acid H’s on same side of the double bond; fold into a U-like formation; naturally occurring Trans-Fatty Acid H’s on the opposite side of the double bond; occur in partially hydrogenated food

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30  linoleic acid and linolenic acid are important for synthesizing arachidonic acid (20 C atoms)  Arachidonic acid in turn is the precursor for the synthesis of eicosanoids  Prostaglandins  Leukotrienes  Thromboxanes Arachidonic acid

 Esterification – Fatty acids react with alcohols to form esters and water  Acid Hydrolysis Producing fatty acids from esters. Opposite of esterification.

 Saponification: Alkaline hydrolysis produces glycerol and salts of fatty acids (soaps).

 Hydrogenation Used in the food industry to convert polyunsaturated vegetable oils into saturated solid fats.  Partial hydrogenation Carried out to add hydrogen to some, but not all, double bonds in polyunsaturated oils In this way liquid vegetable oils are converted into solid form (Crisco and margarine)

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1. Simple Lipids 2. Complex Lipids 3.Precursor & Derived Lipids Lipids

 Esters of fatty acids and alcohol. (trihydric or monohydric alcohol).

 Fats :esters of fatty acids with glycerol. Ex. triglycerides.  Oils : are fats in liquid state.

 Triglycerides are the main dietary fats in human body.  It is a naturally occurring ester of three fatty acids and glycerol that is the chief constituent of fats and oils.  Glycerol forms the “backbone” of the fat.

 Fat: Is solid at room temperature. Is prevalent in meats, whole milk, butter, and cheese.  Oil: Contain high proportion of unsaturated fatty acids and saturated fatty acids. Is liquid at room temperature. Is prevalent in plants such as olive and safflower. corn oil contains 86% unsaturated fatty acids and 14% saturated fatty acids

 Esters of long-chain fatty acids with higher molecular weight monohydric alcohols.  Has a weakly polar head group (ester linkage) and non-polar tails (hydrocarbon chain).  Fatty acids found in waxes are usually saturated ex. stearic acid.  Alcohols may be saturated or unsaturated and may include sterols ex. cholesterol.

Esters of fatty acids with various alcohols along with an additional group. Simple lipid + Additional group = Complex Lipids a. Phospholipids: Glycerophospholipids, Sphingophospholipids. b.Glycolipids c.Other Complex Lipids : Lipoproteins,aminolipids and sulfolipids.

Glycerophospholipids (Phosphoglycerides):  They are phosphate esters.  Structure: Glycerol + 2 Fatty acids + PO4 + polar molecule ( x).

 It is an amphipathic molecule: Fatty acid tails = hydrophobic Polar region (glycerol + carbonyl o of fatty acids + PO 4 + x)= hydrophilic dual “personality” interaction with H 2 O is complex & very important! It likes water & also pushes it away!

 Because of their bipolar nature, when placed in water phospholipids orient themselves in small spheres or “bubbles” with their nonpolar (hydrophobic) regions oriented away from water and their polar (hydrophilic) regions exposed to water.  These structure are called micelles and are similar in structure the cell membrane which is composed in part of a phospholipid bilayer.

Phospholipids of cell membrane double layer = bilayer hydrophilic heads on outside hydrophilic heads on outside in contact with aqueous solution outside of cell and inside of cell hydrophobic tails on inside form core forms barrier between cell & external environment

Sphingophospholipids (Sphingolipids):  Are not glycerides  no glycerol in them  However they are similar to phospholipids  These lipids are based on sphingosine: Long-chain Nitrogen-containing Alcohol  They can be modified by adding different “polar head” groups and non-polar fatty acid “tails”(via amide bond to N atom).

Fatty acids attach here “polar head” groups attach here Sphingophospholipids (Sphingolipids):

Amphipathic, like phospholipids Polar head group and Two non-polar fatty acid tail Structural component of cellular membranes. Major categories: Sphingomyelins Structural lipid of nerve cell membranes. Myelin sheath feature. Glycosphingolipids Also important components of muscle & nerve membranes.

Sphingophospholipids (Sphingolipids):

They are compounds produced when simple and complex lipids undergo hydrolysis. Fatty acids GlycerolSteroidshormones Vitamins (A,D,E,K)

 Steroids are cyclic hydrocarbons usually composed of four rings.  A steroid nucleus consists of :  three cyclohexane rings and one cyclopentane ring.  The rings are fused (4 fused C rings)  different steroids created by attaching different functional groups to rings.  ex: cholesterol, sex hormones and vitamins.

 It is the most common steroid! It is the building block for steroid hormones and also functions in cell membrane structure.  It is an amphipathic molecule (like phospholipids): -OH group  polar Fused rings  non-polar  High levels in blood may contribute to cardiovascular disease.

1.Cell membrane component – Its fused ring portion is readily soluble in the hydrophobic region of membrane – Polar -OH group sticks out of membrane helps keep cell membranes fluid & flexible

2-Precursor to bile salts:  Bile salts made in liver but stored in gall bladder.  Are emulsifying agents that aid in lipid digestion. 3-Vitamin D synthesis:

4.Male and female sex hormones