LipidsLipids(Adapted in part from Larry J. Scheffler, Lincoln High School, 2009)(Adapted in part from Larry J. Scheffler, Lincoln High School, 2009)

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LipidsLipids

Lipids are Lipids are fatsfatsOrganic molecules with long hydrocarbon chainsOrganic molecules with long hydrocarbon chainsHydrophobic (insoluble in water) because they are Hydrophobic (insoluble in water) because they are nonpolar (made of C-C and C-H bonds) nonpolar (made of C-C and C-H bonds) Are soluble in non-polar organic solvents (other oils, Are soluble in non-polar organic solvents (other oils, hexane)hexane)

Lipids are generally divided into three classesLipids are generally divided into three classes1.Triglycerides – Fats and Oils1.Triglycerides – Fats and Oils2. Phospholipids 2. Phospholipids 3 Steroids – Cholesterol3 Steroids – Cholesterol

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Fats and OilsFats and Oils

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Fats and OilsFats and Oils

Fats and oils are Fats and oils are

triesterstriesters formed from formed from the condensation the condensation reaction of glycerol reaction of glycerol (1,2,3,propanetriol) with (1,2,3,propanetriol) with long chain fatty acidslong chain fatty acids

Example:Example:

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FatsFats

Properties of the fat Properties of the fat depends on the kinds of depends on the kinds of fatty acids attached to fatty acids attached to the glycerolthe glycerolFatsFats are generally are generally solids at room solids at room temperaturetemperature

Because their fatty acids Because their fatty acids have have saturated saturated hydrocarbon chainshydrocarbon chains

No C=C bonds, No C=C bonds, “saturated” with “saturated” with HydrogenHydrogen

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OilsOils

while while oilsoils are are usually liquids at usually liquids at room temperatureroom temperatureOilsOils contain contain unsaturated unsaturated hydrocarbonhydrocarbon chainschains, , with with at least 1 C=Cat least 1 C=C..Frequently there are Frequently there are several C=C. They several C=C. They are known as are known as polyunsaturated.polyunsaturated.

Fatty AcidsFatty Acids

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

Stearic: 70Stearic: 70ºCºC

Oleic: 13Oleic: 13ºCºC

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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 carbon atoms in the hydrocarbon chain the hydrocarbon chain form a succession ofform a succession of tetrahedrons tetrahedrons

This regular This regular tetrahedral tetrahedral arrangement of carbon arrangement of carbon atoms makes it atoms makes it possible for it to pack possible for it to pack with parallel chains with parallel chains fairly closely togetherfairly closely together

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Differences in Melting PointsDifferences in Melting Points

Although theAlthough the attractions between attractions between the chainsthe chains are only the are only the rather weakrather weak van der van der Waals attractionsWaals attractions the the large surface area in large surface area in the long carbon chains the long carbon chains groups result in groups result in attractive forces that attractive forces that are strong enough to are strong enough to sustain a solid statesustain a solid state

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Unsaturated Fatty Acids: Unsaturated Fatty Acids: Kinky!Kinky!The presence of the The presence of the C=CC=C in the unsatruated fatty in the unsatruated fatty acid chain changes the acid chain changes the bond angle from about bond angle from about 109 109 ooC to around 120 C to around 120 ooC. C. This “kink” in the carbon This “kink” in the carbon chain keeps the fatty chain keeps the fatty acids from packing as acids from packing as closely together.closely together.As a result the van der As a result the van der Waals forces are weaker Waals forces are weaker and less energy is and less energy is required to separate required to separate them.them.

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Saturated and Saturated Fats and Saturated and Saturated Fats and NutritionNutrition

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 fats.Most animal fats are saturated fats.Vegetable oils are more unsaturated.Vegetable oils are more unsaturated.Oils withOils with one C=C double bondone C=C double bond per fatty acidper fatty acid chain are calledchain are called ““monounsaturatedmonounsaturated oils”oils” Oils with more than one C=C double bond Oils with more than one C=C double bond per fatty acid chain are called per fatty acid chain are called ““polyunsaturatedpolyunsaturated oils”. oils”.

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The Iodine IndexThe Iodine IndexThe 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 oil. Each react with the unsaturated fat or oil. 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 nearlyThe 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. 14

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 (ie - cannot synthesize on its own (ie - -6-6 linoleic linoleic acidacid))

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 AcidsEssential Unsaturated Fatty Acids

-3-3 linolenic acidlinolenic acid is another example of an is another example of an essential fatty acid. It is aessential 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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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 carbohydrates.energy than carbohydrates.

Carbs: ~ 17 kJ/gCarbs: ~ 17 kJ/g Fats: ~ 38 kJ/gFats: ~ 38 kJ/g (Ethanol: ~ 30 kJ/g :/)(Ethanol: ~ 30 kJ/g :/)

Fats require a greater degree of oxidation to become Fats require a 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 atom (think of a glucose ring)carbon atom (think of a glucose ring)

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 FatsIn the body triglycerides, fats and oils, areIn 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 as known as lipaseslipases

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Hydrogenated Fats and OilsHydrogenated Fats and OilsUnsaturated oils can beUnsaturated oils can be hydrogenatedhydrogenated to form to form solid, saturated fats by the solid, saturated fats by the reaction with hydrogen reaction with hydrogen gas in the presence of gas in the presence of nickel or platinum as a nickel or platinum as a catalyst. catalyst.

Ie: Margarine, shortening Ie: Margarine, shortening (Crisco)(Crisco)

Vegetable oils were first Vegetable oils were first hydrogenated for easier hydrogenated for easier transport and storage in transport and storage in 1911.1911.

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Trans Fatty AcidsTrans Fatty Acids

When we synthetically When we synthetically hydrogenate hydrogenate unsaturated fatty acids unsaturated fatty acids to make them into to make them into saturated ones, somesaturated ones, some trans isomerstrans isomers may be may be formed unintentionally.formed unintentionally.Trans fatty acids are Trans fatty acids are found in foods where found in foods where hydrogenated oils are hydrogenated oils are used (fast foods, some used (fast foods, some margarines).margarines).

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Trans Fatty Acid MetabolismTrans Fatty Acid Metabolism

Trans fatty acidsTrans fatty acids are are generally considered generally considered undesirableundesirableThe human The human lipaselipase enzymes help in fat enzymes help in fat digestion by digestion by hydrolyzing the ester hydrolyzing the ester bond in fatty acidsbond in fatty acidsLipase is Lipase is specific to the specific to the cis-configurationcis-configuration, and , and cannot break down cannot break down trans-fatty acidstrans-fatty acids

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Trans Fatty Acid MetabolismTrans Fatty Acid MetabolismTrans-fats float around Trans-fats float around the bloodstream the bloodstream unmetabolized until unmetabolized until they are eventually they are eventually cleared by the livercleared by the liver

Because of this, they Because of this, they build up on blood build up on blood vessel walls and vessel walls and increase risk of increase risk of cardiovascular diseasecardiovascular disease, , heart attack, stroke, heart attack, stroke, etc.etc.

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Trans Fatty Acid and MarketingTrans Fatty Acid and Marketing

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<0.5 g per serving = “0 trans fats” label

Lipid Functions in the BodyLipid Functions in the BodyEnergy 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 have stored in the adipose tissues. Because they have less oxygen per molecule, lipids are oxidized more less oxygen per molecule, lipids are oxidized more slowly, but release more energy.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 L Lipids, especially phospholipids, ipids, 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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PhospholipidsPhospholipids

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PhospholipidsPhospholipidsAA phospholipid phospholipid also also has a glycerol has a glycerol backbonebackbone

But only 2 fatty acid But only 2 fatty acid chainschains

Instead of a third Instead of a third fatty acid, it has a fatty acid, it has a very polar very polar phosphate groupphosphate group

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PhospholipidsPhospholipids

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PhospholipidsPhospholipids

PhospholipidsPhospholipids are one are one of the essential of the essential components ofcomponents of cell cell membranes.membranes.The make a double The make a double layer called the layer called the lipid lipid bilayerbilayer

““Heads” polar because of Heads” polar because of phosphate group – all phosphate group – all face waterface water

““Tails” nonpolar because Tails” nonpolar because of fatty acids – all face of fatty acids – all face each other each other

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Phospholipid FunctionsPhospholipid FunctionsPhospholipids form a significant part of cell membranes. Phospholipids form a significant part of cell membranes.

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

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

Areas of phospholipids can Areas of phospholipids can bud off of and into the cell tobud off of and into the cell to

form vesicles.form vesicles.

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CholesterolCholesterol

CholesterolCholesterolCholesterol has the characteristicCholesterol has the characteristic four ring structurefour ring structure that is that is common to all steroids. common to all steroids.

This we already know from the Hormone Seminar This we already know from the Hormone Seminar Cholesterol isCholesterol is created by the livercreated by the liver, but is also available , but is also available through food.through food.If you ate no cholesterol at all, your body would still If you ate no cholesterol at all, your body would still produce enough for you to live perfectly wellproduce enough for you to live perfectly well

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Cholesterol FunctionsCholesterol FunctionsCholesterol is Cholesterol is necessary necessary in the human body. in the human body. It acts as a building block to create other It acts as a building block to create other steroids (sex hormones, adrenocorticoid steroids (sex hormones, adrenocorticoid hormones) as well as essential substances hormones) as well as essential substances such as vitamin D. such as vitamin D.

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

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Cholesterol is AwesomeCholesterol is Awesome

Cholesterol is inserted Cholesterol is inserted into the phospholipid into the phospholipid bilayer of your cell bilayer of your cell membranemembrane

It acts to make your cell It acts to make your cell membrane more rigid in membrane more rigid in the summer (so your the summer (so your cells don’t melt), AND cells don’t melt), AND more fluid in the winter more fluid in the winter (so they don’t freeze).(so they don’t freeze). http://www.hcc.bcu.ac.uk/physiology/phospholipid02.gif

Cholesterol is evil?Cholesterol is evil?

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LDL and HDLLDL and HDLCholesterol is very hydrophobic – it can’t exist in our Cholesterol is very hydrophobic – it can’t exist in our water-based blood alonewater-based blood aloneIt is transported around the body by lipoproteins.It is transported around the body by lipoproteins. These wrap around it to make it capable of moving These wrap around it to make it capable of moving through the bloodstream.through the bloodstream.These are Low Density Lipoprotein (LDL) and High These are Low Density Lipoprotein (LDL) and High Density Lipoprotein (HDL)Density Lipoprotein (HDL)They have two different roles in cellsThey have two different roles in cells

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LDL: “Bad” cholesterolLDL: “Bad” cholesterol

Low density lipoproteins (LDL)Low density lipoproteins (LDL) are larger, are larger, ranging from 18-25nm.ranging from 18-25nm.

LDL LDL is a large bulky molecule, therefore it is a large bulky molecule, therefore it deposits cholesterol on blood vessel deposits cholesterol on blood vessel walls.walls.

LDL is what the body uses to transport LDL is what the body uses to transport cholesterol “out” to cells from the liver.cholesterol “out” to cells from the liver. LDL molecules are made from saturated fats, LDL molecules are made from saturated fats,

especially lauric (C12), myristic (C14) and especially lauric (C12), myristic (C14) and palmitic (C16) acids.palmitic (C16) acids.

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HDL: “Good” CholesterolHDL: “Good” Cholesterol

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

HDL can remove cholesterol from the HDL can remove cholesterol from the arteriesarteries and transport it back to the liver.and transport it back to the liver.

HDL is what the liver uses to “bring HDL is what the liver uses to “bring cholesterol back” to break it downcholesterol back” to break it down

The End The End

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