LipidsLipids

IB Chemistry 3-4IB Chemistry 3-4

Lincoln High SchoolLincoln High School

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LipidsLipids

• Lipids are organic molecules with long Lipids are organic molecules with long hydrocarbon chains that are soluble in hydrocarbon chains that are soluble in non-polar organic solventsnon-polar organic solvents

• Lipids are generally divided into three Lipids are generally divided into three classesclasses

• 1.Triglycerides – Fats and Oils1.Triglycerides – Fats and Oils

• 2. Phospholipids – lecithin2. Phospholipids – lecithin

• 3 Steroids -- Cholesterol3 Steroids -- Cholesterol

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Fats and OilsFats and Oils• Fats and oils are triesters formed from the Fats and oils are triesters formed from the

condensation reaction of glycerol (1,2,3 condensation reaction of glycerol (1,2,3 propanetriol) with long chain fatty acidspropanetriol) with long chain fatty acids

• Example:Example:

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Lipids Lipids The three fatty acid chains do not necessarily The three fatty acid chains do not necessarily have to be identical. Each of the three fatty have to be identical. Each of the three fatty acids forming the triglyceride can be a acids forming the triglyceride can be a different fatty acid.different fatty acid.

Fats and OilsFats and Oils

• Fats are generally solids at room Fats are generally solids at room temperature, while oils are usually temperature, while oils are usually liquidsliquids

• FatsFats containcontain saturated hydrocarbon saturated hydrocarbon chainschains

• OilsOils containcontain unsaturated hydrocarbonunsaturated hydrocarbon chainschains, with , with at least 1 C=Cat least 1 C=C. . Frequently Frequently there are several C=C. They are known there are several C=C. They are known as polyunsaturated.as polyunsaturated.

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Fatty AcidsFatty Acids

• Stearic acid and linoleic acid have the same Stearic acid and linoleic acid have the same number of carbon atoms but very different number of carbon atoms but very different melting points.melting points.

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Common Fatty AcidsCommon Fatty AcidsName Formula Source

Saturated Fatty Acids

Lauric Acid CH3-(CH2)10-COOH Coconut Oil

Palmitic Acid CH3-(CH2)14-COOH Palm Oil

Stearic Acid CH3-(CH2)16-COOH Animal and vegetable fats

Arachidic Acid CH3-(CH2)18-COOH Peanut Oil

Unsaturated Fatty Acids

Oleic Acid

CH3-(CH2)7CH=CH-(CH2)7COOH Corn Oil

Linoleic Acid

CH3-(CH2)4 CH=CH-CH2-CH=CH –

(CH2)7COOHLinseed Oil

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Differences in Melting PointsDifferences in Melting Points• The carbon atoms in the hydrocarbon chain form a succession of The carbon atoms in the hydrocarbon chain form a succession of

tetrahedrons tetrahedrons • This regular tetrahedral arrangement of carbon atoms makes it possible for it This regular tetrahedral arrangement of carbon atoms makes it possible for it

to pack with parallel chains fairly closely togetherto pack with parallel chains fairly closely together• Although the Although the attractions between the chainsattractions between the chains are only the rather weak are only the rather weak van der van der

Waals attractionsWaals attractions the large surface area in the long carbon chains groups the large surface area in the long carbon chains groups result in attractive forces that are strong enough to sustain a solid state result in attractive forces that are strong enough to sustain a solid state

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Unsaturated Fatty AcidsUnsaturated Fatty Acids

• The presence of the C=C in the unsatruated The presence of the C=C in the unsatruated fatty acid chain changes the bond angle from fatty acid chain changes the bond angle from about 109 about 109 ooC to around 120 C to around 120 ooC. C.

• This “kink” in the carbon chain keeps the This “kink” in the carbon chain keeps the fatty acids from packing as closely together.fatty acids from packing as closely together.

• As a result the van der Waals forces are As a result the van der Waals forces are weaker and less energy is required to weaker and less energy is required to separate them.separate them.

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Saturated and Saturated Fats Saturated and Saturated Fats and Nutritionand Nutrition

• Saturated and unsaturated fats are terms Saturated and unsaturated fats are terms most commonly used in the context of most commonly used in the context of nutrition. nutrition.

• Most animal fats are saturated fatsMost animal fats are saturated fats. They are . They are usually usually solidssolids at room temperature. at room temperature.

• Vegetable oils are more unsaturatedVegetable oils are more unsaturated. They . They areare liquids liquids at room temperature. at room temperature.

• Oils with Oils with one C=C double bondone C=C double bond per fatty acid per fatty acid chain are called “chain are called “monounsaturatedmonounsaturated oils” oils”

• Oils with Oils with more than one C=C double bondmore than one C=C double bond per fatty acid chainper fatty acid chain are calledare called “polyunsaturated“polyunsaturated oils”.oils”.

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Hydrogenated Fats and OilsHydrogenated Fats and Oils

• Unsaturated oils can be Unsaturated oils can be hydrogenatedhydrogenated to to form solid, saturated fats by the reaction with form solid, saturated fats by the reaction with hydrogen gas in the presence of nickel or hydrogen gas in the presence of nickel or platinum as a catalyst. platinum as a catalyst.

• Margarine is an example of a hydrogenated Margarine is an example of a hydrogenated oil.oil.

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The Iodine IndexThe Iodine Index• The degree of unsaturation can be measured The degree of unsaturation can be measured

by measuring the amount of iodine that can by measuring the amount of iodine that can react with the unsaturated fat or oilreact with the unsaturated fat or oil.. Each Each mole of C=C requires one mole of Imole of C=C requires one mole of I22 to react. to react.

• The haloalkane chain is nearly The haloalkane chain is nearly colorlesscolorless Therefore unsaturated hydrocarbon chains Therefore unsaturated hydrocarbon chains will destroy the purple brown color of iodine will destroy the purple brown color of iodine solutions as long as there are C=C bonds solutions as long as there are C=C bonds present.present.

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Iodine Index of Common Fats/ OilsIodine Index of Common Fats/ Oils

Oil or fat Percentsaturated

fats

Percent of monounsaturated fats

Percent of polyunsaturated fats

Iodine Index

Butter fat 67% 29% 4% 34BeefTallow

52% 44% 4% 50

Olive Oil 15% 75% 10% 81

Peanut Oil 18% 49% 33% 93

Canola Oil 7% 62% 31% 130Sunflower

oil10% 13% 77% 125

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Essential Fatty AcidsEssential Fatty Acids

• Most naturally occuring fats are a mixture of Most naturally occuring fats are a mixture of saturated, monounsaturated and saturated, monounsaturated and polyunsaturated fatty acidspolyunsaturated fatty acids

• Essential fatty acidsEssential fatty acids are those that the body are those that the body cannot synthesize on its own.cannot synthesize on its own.

• They must be acquired from the foods we They must be acquired from the foods we eat.eat.

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Essential Unsaturated Fatty Essential Unsaturated Fatty AcidsAcids

-6-6 linoleic acidlinoleic acid is an example of an is an example of an essential fatty acid. It is a cis isomer. Theessential fatty acid. It is a cis isomer. The --66 indicates that there is a C=C on the 6indicates that there is a C=C on the 6thth carbon from the end of the carbon chaincarbon from the end of the carbon chain

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Essential Unsaturated Fatty Essential Unsaturated Fatty AcidsAcids

-3-3 linolenic acidlinolenic acid is another example of an is another example of an essential fatty acid. It is a essential fatty acid. It is a ciscis isomer. The isomer. The --33 indicates that there is a C=C on the 3rd indicates that there is a C=C on the 3rd carbon from the end of the carbon chaincarbon from the end of the carbon chain

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Trans Fatty AcidsTrans Fatty Acids• When fatty acids are made synthetically by When fatty acids are made synthetically by

partially hydrogenating other polyunsaturated partially hydrogenating other polyunsaturated fatty acids, some fatty acids, some trans isomerstrans isomers may be may be formed.formed.

• Trans fatty acids are found in fried foods and Trans fatty acids are found in fried foods and in some margarines.in some margarines.

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Trans Fatty AcidsTrans Fatty Acids• Trans fatty acidsTrans fatty acids are generally considered are generally considered

undesirable since theyundesirable since they increase the increase the formation of LDL Cholesterolformation of LDL Cholesterol and hence the and hence the risk of heart disease.risk of heart disease.

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Fat MetabolismFat Metabolism• Fats metabolism occurs more slowly than Fats metabolism occurs more slowly than

carbohydrates metabolism but fats provide more carbohydrates metabolism but fats provide more energy than carbohydratesenergy than carbohydrates..

• Fats require greater degree of oxidation to become Fats require greater degree of oxidation to become COCO22 and H and H22O than carbohydrates because O than carbohydrates because carbohydrates already have one oxygen for every carbohydrates already have one oxygen for every carbon atomcarbon atom

• The number of oxygen molecules needed to oxidize a The number of oxygen molecules needed to oxidize a fat is greater than for carbohydrates., The oxidation of fat is greater than for carbohydrates., The oxidation of fats takes longer, but it also generates more energy. fats takes longer, but it also generates more energy.

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Hydrolysis of FatsHydrolysis of Fats• In the body triglycerides, fats and oils, are In the body triglycerides, fats and oils, are

hydrolyzedhydrolyzed to fatty acids by the action of enzymes to fatty acids by the action of enzymes known asknown as lipaseslipases

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Hydrolysis of FatsHydrolysis of Fats• Triglycerides are broken down in the presence of Triglycerides are broken down in the presence of

strong bases such as NaOH or KOH. The sodium or strong bases such as NaOH or KOH. The sodium or potassium salt of a fatty acid is a SOAPpotassium salt of a fatty acid is a SOAP

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PhospholipidsPhospholipids• A A phospholipid phospholipid has one of the three carbon chains of a has one of the three carbon chains of a

triglyceride is replaced with a more polar phosphate-triglyceride is replaced with a more polar phosphate-containing group.containing group.

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Four parts of a phospholipid

Phospholipids

PhospholipidsPhospholipids• In a In a phospholipidsphospholipids are one of the essential components are one of the essential components

of of cell membranes.cell membranes.• Phosphatidyl Choline, an example of a phospholipid, has Phosphatidyl Choline, an example of a phospholipid, has

this structure: this structure:

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• Phosphatidyl choline is a major component of lecithin found in egg yolk,

Phospholipid FunctionsPhospholipid Functions• Phospholipids form a significant part of cell membranes. Phospholipids form a significant part of cell membranes.

• The cell membrane must protect the cell form the The cell membrane must protect the cell form the intercellular fluids around it. At the same time it must allow intercellular fluids around it. At the same time it must allow cell nutrients to enter the cell and waste products to leavecell nutrients to enter the cell and waste products to leave. .

• Phospholipids tend to formPhospholipids tend to form bilayers in aqueous solutions. bilayers in aqueous solutions.

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Phospholipid FunctionsPhospholipid Functions

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• The polar heads interface The polar heads interface with water and the non-polar with water and the non-polar tails are attracted to non-tails are attracted to non-polar tissues. polar tissues.

• The larger phospholipids The larger phospholipids can open and close to form can open and close to form vesicles. It is believed that vesicles. It is believed that this behavior is important to this behavior is important to the functioning of the porous the functioning of the porous cell membranescell membranes

Steroids

SteroidsSteroids

• Steroids have a characteristic structure with four rings

CholesterolCholesterol• Cholesterol has the characteristic Cholesterol has the characteristic four ring structurefour ring structure

that is common to all steroids. that is common to all steroids. • Cholesterol exists in Cholesterol exists in esterifiedesterified form in fatty acids form in fatty acids

and in a free form. and in a free form. • Cholesterol is Cholesterol is created by the livercreated by the liver, but is also , but is also

available through food.available through food.

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Cholesterol FunctionsCholesterol Functions• Cholesterol is the most common, important and Cholesterol is the most common, important and

necessary steroidnecessary steroid in the human body. in the human body.

• It is component of all tissues and is found in the It is component of all tissues and is found in the blood, brain and the spinal cord. blood, brain and the spinal cord.

• It also acts as a building block to create other It also acts as a building block to create other steroids such as sex hormones and adrenocorticoid steroids such as sex hormones and adrenocorticoid hormones as well as essential substances such as hormones as well as essential substances such as vitamin D. vitamin D.

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LDL and HDLLDL and HDL• Cholesterol is transported around the body by Cholesterol is transported around the body by

lipoproteins. lipoproteins. • Low density lipoproteins (LDL)Low density lipoproteins (LDL) range from 18-25nm range from 18-25nm• LDL LDL transport cholesterol to the arteriestransport cholesterol to the arteries where it can build where it can build

up and cause cardiovascular diseaseup and cause cardiovascular disease• LDL result from saturated fats, especially lauric (C12), LDL result from saturated fats, especially lauric (C12),

myristic (C14) and palmitic (C16) acids.myristic (C14) and palmitic (C16) acids.

• High density lipoproteins (HDL)High density lipoproteins (HDL) are smaller, ranging from are smaller, ranging from 8-11 nm.8-11 nm.

• HDL can remove cholesterol from the arteriesHDL can remove cholesterol from the arteries and and transport it back to the liver.transport it back to the liver.

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Sex Hormones

Sex hormones such as androgens (male sex hormones), estrogens (female sex hormones) and progestins are present in the male and female.

Lipid Functions in the BodyLipid Functions in the Body• Energy storageEnergy storage Lipids are highly efficient Lipids are highly efficient

energy stores for most higher animals. Fats are energy stores for most higher animals. Fats are stored in the adipose tissues. Because they stored in the adipose tissues. Because they have less oxygen per molecule, lipids are have less oxygen per molecule, lipids are oxidized more slowly, but release more energy.oxidized more slowly, but release more energy.

• Thermal insulation and protectionThermal insulation and protection Fats Fats provide thermal insulation for the body.provide thermal insulation for the body.

• Cell Structure Cell Structure Lipids, especially phospholipids, Lipids, especially phospholipids, form a significant part of most cell membranes. form a significant part of most cell membranes. They protect the cell from the intercellular fluids They protect the cell from the intercellular fluids around it and play an important role in the around it and play an important role in the transport of fluids into and out of the cell.transport of fluids into and out of the cell.

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The endThe end

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