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L.Noha Soliman
LIPIDS
Biochemistry(BMS 233)
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2
OBJECTIVES
• Definition of lipids.• Functions of lipids.• Fatty acids
• Classifications of fatty acids.• Chemical reactions of fatty
acids.• Classification of lipids.
• Simple lipids.• Complex lipids.• Precursor and derived lipids.
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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.
Definition
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Functions of lipids
A.The Functions of Fat in the Body:1. Energy source esp. for muscles.
2. Serves as an energy reserve.
Lipid (TGL)Droplets InAdipose tissue
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Functions of lipids
3. Cell Membrane Structural components
4. Cushion the vital organs to protect them from shock.
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Functions of lipids
5. Thermal Insulator :
Subcutaneous layer of fat reduces heat loss in cold weather (helps maintain body temperature).
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Functions of lipids
B. The Functions of Fat in Food:1.Provide calories (9 kcal per gram).
2.Provide satiety.
3.Carry Lipid-soluble vitamins (A,D,E, and K) & essential fatty acids.
4.Contribute aroma & flavor.
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Adipose cells swollen with fat ! ! ! ! !
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!!!
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Bad Things About Fat
• Makes you fat!
• Heart disease, high blood pressure, cancer.
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Fatty acids
Are long-chain monocarboxylic acids.
Generally contain an even number of carbon atoms.
General formula is CH3 (CH2)n COOH.
O
R C OH
#1 Carbon Acid Group
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Classification of fatty acids
• 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
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Classification of fatty acids
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)
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Fat saturation
Saturation means “full”, so what could they be full of?
Full of H atoms! And wherever there is a chemical bond, there is stored energy.
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General Formula: CH3 (CH2)n COOH.
Each C being “saturated” with H.
Contain only single C–C bonds.
long, straight chain.
Properties of saturated fatty acids
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Properties of saturated fatty acids
Closely packed.
Strong attractions between
chains.
High melting points.
Solids at room temperature.
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Properties of saturated fatty acids
Animal foods such as meat,
poultry and full-fat dairy
products.
Tropical oils such as palm and
coconut.
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Properties of saturated fatty acids
Contributes to cardiovascular disease.
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Properties of unsaturated fatty acids
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.
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Properties of unsaturated fatty acids
Low melting points
Liquids at room temperature
Plant & fish fats Vegetable oils
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saturated unsaturated
Saturated VS Unsaturated
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Fatty acids may be further subdivided as follows
1. Monounsaturated FA
2. Polyunsaturated FA
3. Eicosanoids
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Fatty acids may be further subdivided as follows
1. Monounsaturated Fatty Acids (MUFA)
Containing one double bond.
Oleic (most common FA) 18:1;9
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Fatty acids may be further subdivided as follows
2. Polyunsaturated Fatty Acids (PUFA)Containing two or more double bonds
Linoleic (corn, peanut, cottonseed) 18:2;9,12
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– Are identified by position of the double bond nearest the methyl end (CH3) 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
Polyunsaturated Fatty acids
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ω3, ω6, ω9 Fatty Acids
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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
Cis &Trans Fatty acids
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Cis - Fatty acids
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Trans - Fatty acids
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Essential & nonessential fatty acids
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Essential fatty acids
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
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Chemical reactions of fatty acids
Esterification – Fatty acids react with alcohols to form esters and water
Acid Hydrolysis
Producing fatty acids from esters.Opposite of esterification.
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Chemical reactions of fatty acids
Saponification:Alkaline hydrolysis produces glycerol and salts of fatty acids
(soaps).
CH 2 O
C HO
CH 2
C
C
O C
R1
R3
R2
O
O
OH2C OH
C HHO
H2C OH
ON aCR1
O
ON aCR3
O
+ ON aCR2
O
Triacylglycerol Glycerol Sodium salts of fatty acids (soap)
3 NaOH
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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)
Reactions at the double bond of unsaturated fatty acids
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1. Simple Lipids
2. Complex Lipids
3.Precursor & Derived Lipids
Lipids
Classification of lipids
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Simple lipids
Esters of fatty acids and alcohol. (trihydric or monohydric alcohol).
CH 2R
Fatty alcoholOH C R
Fatty acidHO
O
+
H2O
CH 2R O C R
O
Esterase (lipase) ester (lipid)
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Simple lipids
FAT and OIL
Fats :esters of fatty acids with glycerol.
Ex. triglycerides.
Oils : are fats in liquid state.
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Triglycerides
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.
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Triglycerides
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Fat VS Oil
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
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Waxes
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.
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Complex lipids
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.
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Phospholipids
Glycerophospholipids (Phosphoglycerides): They are phosphate esters.
Structure: Glycerol + 2 Fatty acids + PO4 + polar molecule ( x).
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Phospholipid structure
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Phospholipid structure
It is an amphipathic molecule:• Fatty acid tails = hydrophobic• Polar region (glycerol + carbonyl o of fatty acids + PO4 + x)= hydrophilic • dual “personality”
interaction with H2O is complex & very important!
It likes water & also pushes it away!
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Phospholipid behavior
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.
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Phospholipid & cells
• Phospholipids of cell membrane
double layer = bilayer
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
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Phospholipids
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).
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Fatty acids attach here
“polar head” groups
attach here
Phospholipids
Sphingophospholipids (Sphingolipids):
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Phospholipids
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.
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Phospholipids
Sphingophospholipids (Sphingolipids):
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Precursor and derived lipids
They are compounds produced when simple and complex lipids undergo hydrolysis.
Fatty acids
Glycerol
Steroids
hormones
Vitamins (A,D,E,K)
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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.
Steroids
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Cholesterol
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.
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Importance of cholesterol in the body
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
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Importance of cholesterol in the body
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:
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Importance of cholesterol in the body
3-Vitamin D synthesis:
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Importance of cholesterol in the body
4. Male and female sex hormones
O
CH3
CH3
C
CH3
O
progesterone
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