Chem 150 Chem 150 Unit 5 - Biological Unit 5 - Biological Molecules I Molecules I Lipids Lipids Like organic molecules, biological molecules are Like organic molecules, biological molecules are grouped into families. There are four major grouped into families. There are four major families of biological molecules, including families of biological molecules, including proteins proteins , , nucleic acids nucleic acids , , carbohydrates carbohydrates , and , and lipids lipids . The lipids are the subject of this unit. . The lipids are the subject of this unit. Of these four families, the lipids are the Of these four families, the lipids are the structurally the most diverse. This is because structurally the most diverse. This is because unlike members of the other three families, unlike members of the other three families, members of this families do no share a common members of this families do no share a common structural feature, but rather share a common structural feature, but rather share a common physical property; the are hydrophobic. physical property; the are hydrophobic.
Like organic molecules, biological molecules are Like organic molecules, biological molecules are grouped into families. There are four major families grouped into families. There are four major families of biological molecules, including of biological molecules, including proteinsproteins, , nucleic nucleic acidsacids, , carbohydratescarbohydrates, and , and lipidslipids. The lipids are . The lipids are the subject of this unit. Of these four families, the the subject of this unit. Of these four families, the lipids are the structurally the most diverse. This is lipids are the structurally the most diverse. This is
because unlike members of the other three families, because unlike members of the other three families, members of this families do no share a common members of this families do no share a common structural feature, but rather share a common structural feature, but rather share a common
physical property; the are hydrophobic.physical property; the are hydrophobic.
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IntroductionIntroduction
Lipids are hydrophobic, nonpolar molelcules.Lipids are hydrophobic, nonpolar molelcules.
• They are soluble in nonpolar solvent.They are soluble in nonpolar solvent.
• They are insoluble in polar solvents, such as waterThey are insoluble in polar solvents, such as water
They are isolated from the other biological molecules by They are isolated from the other biological molecules by extracting them with nonpolar solvents.extracting them with nonpolar solvents.
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IntroductionIntroduction
The types of lipids that we will look at include.The types of lipids that we will look at include.• Fatty AcidsFatty Acids
• In the carboxylic acid familyIn the carboxylic acid family
The common fatty acids found in biological systems are The common fatty acids found in biological systems are shown in Table 8.1 of Raymond.shown in Table 8.1 of Raymond.
TextTextTextText
Linolenic acid is one of the Linolenic acid is one of the omega-3 fatty acids..Linolenic acid is one of the Linolenic acid is one of the omega-3 fatty acids..
Normally the double bonds are Normally the double bonds are ciscis• This lowers the melting points for fatty acids containing This lowers the melting points for fatty acids containing
double bonds.double bonds.
No. of Double BondsNo. of Double BondsNo. of Double BondsNo. of Double Bonds
Me
ltin
g T
em
pe
ratu
re
Me
ltin
g T
em
pe
ratu
re {
°C}
{°C
}M
elti
ng
Te
mp
era
ture
M
elti
ng
Te
mp
era
ture
{°C
}{°
C}
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Fatty AcidsFatty Acids
The The ciscis double bonds produce kinks, which disrupt the double bonds produce kinks, which disrupt the London forces by preventing the tails from packing close to London forces by preventing the tails from packing close to one another.one another.
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Fatty AcidsFatty Acids
As acids, the carboxylic acid group in fatty acids can react As acids, the carboxylic acid group in fatty acids can react with a base to produce a carboxylate ionwith a base to produce a carboxylate ion• By donating its proton (HBy donating its proton (H++) to the base the fatty acid ) to the base the fatty acid
becomes negatively charged.becomes negatively charged.• We will talk more about acids and bases in Unit 6We will talk more about acids and bases in Unit 6
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Fatty AcidsFatty Acids
The negative charge makes the polar head portion of the the The negative charge makes the polar head portion of the the fatty acid even more more polar and hydrophilic.fatty acid even more more polar and hydrophilic.
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Fatty AcidsFatty Acids
The salts of fatty acids are also called The salts of fatty acids are also called soapssoaps, and are , and are considered considered amphipathicamphipathic, , meaning they have a part that is meaning they have a part that is very very hydrophobichydrophobic along with a part that is very along with a part that is very hydrophilichydrophilic..
• In Unit 3 we discussed how amphipathic molecules form In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.interesting structures when exposed to water.
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Biochemical Compounds &Biochemical Compounds &Their Interactions with Water Their Interactions with Water (Unit 3)
When placed in water, When placed in water, amphipathic molecules, amphipathic molecules, form structures, such as form structures, such as micelles, which attempt to micelles, which attempt to address the conflict.address the conflict.
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Fatty AcidsFatty Acids
The salts of fatty acids are also called The salts of fatty acids are also called soapssoaps, and are , and are considered considered amphipathicamphipathic, , meaning they have a part that is meaning they have a part that is very very hydrophobichydrophobic along with a part that is very along with a part that is very hydrophilichydrophilic..
• In Unit 3 we discussed how amphipathic molecules form In Unit 3 we discussed how amphipathic molecules form interesting structures when exposed to water.interesting structures when exposed to water.
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WaxesWaxes
Waxes are made by combining fatty acids with long chain Waxes are made by combining fatty acids with long chain alcohols.alcohols.
• In Unit 2 we discussed how In Unit 2 we discussed how carboxylic acidscarboxylic acids react with react with alcoholsalcohols to from to from estersesters..
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We look now at three families that are distinguished by a We look now at three families that are distinguished by a functional group that contains the element oxygen.functional group that contains the element oxygen.
EstersEsters• Chemically, esters can be synthesize by reacting a Chemically, esters can be synthesize by reacting a
carboxylic acid with and alcohol:carboxylic acid with and alcohol:
When two more molecules combine to form a larger When two more molecules combine to form a larger molecule, the word molecule, the word residueresidue is used to indicate which is used to indicate which molecule that part of the the larger molecule came from.molecule that part of the the larger molecule came from.
came from the alcoholcame from the alcoholcame from the alcoholcame from the alcoholcame from the fatty acidcame from the fatty acidcame from the fatty acidcame from the fatty acid
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WaxesWaxes
Waxes are very hydrophobic and are used by plants and Waxes are very hydrophobic and are used by plants and animals for protective, water-proof coatingsanimals for protective, water-proof coatings
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QuestionsQuestions
Draw the skeletal structures for the products formed when Draw the skeletal structures for the products formed when beeswax undergoes base-catalzyed hydrolysis beeswax undergoes base-catalzyed hydrolysis (saponification).(saponification).
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Reactions Involving Water (Unit 4)Reactions Involving Water (Unit 4)
HydrolysisHydrolysis• HydrolysisHydrolysis can also be catalyzed using a base (OH can also be catalyzed using a base (OH--):.):.
• Because one of the products of the hydrolysis is a carboxylic acid, in base Because one of the products of the hydrolysis is a carboxylic acid, in base catalyzed hydrolysis the base undergoes a second acid/base reaction with the catalyzed hydrolysis the base undergoes a second acid/base reaction with the carboxylic acid to produce a carboxylate ion.carboxylic acid to produce a carboxylate ion.
• The base catalyzed hydrolysis of esters is also called The base catalyzed hydrolysis of esters is also called saponificationsaponification
• We will be discussing acids and bases in Unit 6We will be discussing acids and bases in Unit 6
H2O
OH-CH2 C
O
O CH2 CH3+
ethylbutanoate(an ester)
butanoate ion(a carobxylate ion)
ethanol(an alcohol)
HOCH3 CH2 CH2 C
O
O CH2 CH3 CH2CH3
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TriglyceridesTriglycerides
TriglyceridesTriglycerides are a storage form of fatty acids in mammals. are a storage form of fatty acids in mammals.
• Often when blood tests are done, they measure your Often when blood tests are done, they measure your triglycyeride levels.triglycyeride levels.
• High triglyceride levels in the blood are a risk indicator for High triglyceride levels in the blood are a risk indicator for artherosclerosisartherosclerosis..
**American Heart Association**American Heart Association
Triglycerides are a combination of three 3 fatty acid Triglycerides are a combination of three 3 fatty acid molecules with a glycerol molecule.molecules with a glycerol molecule.
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TriglyceridesTriglycerides
GlycerolGlycerol, which is also called glycerin, , which is also called glycerin, is an alcohol with three hydroxyl is an alcohol with three hydroxyl groups.groups.
• As with the waxes, the fatty acids As with the waxes, the fatty acids can react with the hydroxyl groups to can react with the hydroxyl groups to form esters.form esters.
• Since there are three hydroxyl Since there are three hydroxyl groups, three fatty acids can react to groups, three fatty acids can react to form three esters.form three esters.
CH2
CH
CH2
HO
HO
HO
glycerol
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TriglyceridesTriglycerides
For triglycerides, all three hydroxyls of the glycerol have a For triglycerides, all three hydroxyls of the glycerol have a fatty acid residue attached to it.fatty acid residue attached to it.
CH2
CH
CH2
O
O
O
glycerolresidue
C
O
CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
C
O
CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
C
O
CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
fatty acidresidues
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Figure 8.6Figure 8.6fromfrom
RaymondRaymond
Figure 8.6Figure 8.6fromfrom
RaymondRaymond
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TriglyceridesTriglycerides
Just as with fatty acids, where the presence of Just as with fatty acids, where the presence of ciscis double double bonds lower the melting points, triglycerides made from bonds lower the melting points, triglycerides made from unsaturated fatty acids have lower melting points than those unsaturated fatty acids have lower melting points than those made from saturated fatty acids.made from saturated fatty acids.
• Triglycerides from animals tend to have a higher proportion Triglycerides from animals tend to have a higher proportion of saturated fatty acids.of saturated fatty acids.
• Most are solids at room temperature and are called Most are solids at room temperature and are called fatsfats. .
• Examples include: butter, lard and bacon greaseExamples include: butter, lard and bacon grease
• Triglycerides from plants tend to have a higher proportion Triglycerides from plants tend to have a higher proportion of unsaturated fatty acids.of unsaturated fatty acids.
• Most are liquids at room temperature and are called Most are liquids at room temperature and are called oilsoils..
Triglycerides as primarily used as a form of stored energy.Triglycerides as primarily used as a form of stored energy.
• This is why when you eat more than you need to meet your This is why when you eat more than you need to meet your energy requirements, the excess energy is stored in the energy requirements, the excess energy is stored in the form of fat.form of fat.
• Fat can store almost twice as much energy per gram as Fat can store almost twice as much energy per gram as carbohydrates and proteinscarbohydrates and proteins
• In mammals the fats are stored in the In mammals the fats are stored in the adipose tissueadipose tissue..
• Adipose tissue also functions to protect organs from shock Adipose tissue also functions to protect organs from shock and cold.and cold.
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TriglyceridesTriglycerides
Reactions that involve triglycerides include:Reactions that involve triglycerides include:
Monoglycerides and fattyacids are absorbed byintestines - transportedas chylomicrons in lymphsystem to blood.-Fat Blocker-Xenical (Alli)
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Transport of fats:
Fat Blocker-Xenical (Alli)
O
O
O
H
O
O
Typical diacylglycerolTypical diacylglycerol
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Fun Topic !: Fake Fats
Olestra: sucrose fatty acid ester(s)
Fat : glycerol fatty acid ester(s)
Side effects?
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TriglyceridesTriglycerides
Hydrogenation of triglyceridesHydrogenation of triglycerides
• This is the same reaction that we saw in Unit 4 with the This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes.hydrogenation of alkenes.
• Unsaturated fatsUnsaturated fats and oils contain alkenes and can be hydrogenated and oils contain alkenes and can be hydrogenated to produce to produce saturated fatssaturated fats..
• Commercially, vegetable oils are often hydrogenated to produce a Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making baked goods.solid product that has better qualities for making baked goods.
‣ Animal fats, such as butter and lard, which are naturally saturated, can Animal fats, such as butter and lard, which are naturally saturated, can also be used, but unlike the vegetable oils, they come with cholesterol, also be used, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.which is undesirable for health reasons.
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Oxidation and Reduction (Unit 4)Oxidation and Reduction (Unit 4)
HydrogenationHydrogenation• Another type of oxidation/reduction reaction is the Another type of oxidation/reduction reaction is the
hydrogenationhydrogenation reaction: reaction:
• In this example, an alkene is reduced to an alkane.In this example, an alkene is reduced to an alkane.
‣ This is considered reduction, because the hydrogen is bringing in additional This is considered reduction, because the hydrogen is bringing in additional electrons to the molecule.electrons to the molecule.
• The alkane that is produced in this reaction is considered “saturated” because it The alkane that is produced in this reaction is considered “saturated” because it can no longer absorb any more hydrogen atoms.can no longer absorb any more hydrogen atoms.
Hydrogenation of triglyceridesHydrogenation of triglycerides
• This is the same reaction that we saw in Unit 4 with the This is the same reaction that we saw in Unit 4 with the hydrogenation of alkenes.hydrogenation of alkenes.
• Unsaturated fatsUnsaturated fats and oils contain alkenes and can be and oils contain alkenes and can be hydrogenated to produce hydrogenated to produce saturated fatssaturated fats..
• Commercially, vegetable oils are often hydrogenated to Commercially, vegetable oils are often hydrogenated to produce a solid product that has better qualities for making produce a solid product that has better qualities for making baked goods.baked goods.
• Animal fats, such as butter and lard, which are naturally saturated, Animal fats, such as butter and lard, which are naturally saturated, can also be used in baking, but unlike the vegetable oils, they come can also be used in baking, but unlike the vegetable oils, they come with cholesterol, which is undesirable for health reasons.with cholesterol, which is undesirable for health reasons.
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TriglyceridesTriglycerides
Hydrogenation of triglyceridesHydrogenation of triglycerides
• Total hydrogenationTotal hydrogenation
liquidliquidliquidliquid solidsolidsolidsolid
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TriglyceridesTriglycerides
Hydrogenation of triglyceridesHydrogenation of triglycerides
• Partial hydrogenationPartial hydrogenation
liquidliquidliquidliquid solidsolidsolidsolid
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TriglyceridesTriglycerides
Hydrogenation of Hydrogenation of triglyceridestriglycerides
• Partial Partial hydrogenation hydrogenation cab produce cab produce transtrans fats. fats.
• Trans fats have Trans fats have been found to been found to lower your HDL lower your HDL (“Good (“Good cholesterol”) cholesterol”) levels.levels.
Oxidation of triglyceridesOxidation of triglycerides
• Unsaturated triglycerides can react with oxygen to produce Unsaturated triglycerides can react with oxygen to produce small change fatty acids another small molecules.small change fatty acids another small molecules.
• These often do not smell very goodThese often do not smell very good
• This is what happens when butter goes rancid.This is what happens when butter goes rancid.
• This makes solid fats and oils more stable than liquid oils This makes solid fats and oils more stable than liquid oils and is why the solid fats are preferred for deep frying.and is why the solid fats are preferred for deep frying.
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TriglyceridesTriglycerides
Oxidation of triglyceridesOxidation of triglycerides
These stink !These stink !These stink !These stink !
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TriglyceridesTriglycerides
Saponification of triglyceridesSaponification of triglycerides
• Saponification is the base-catalyzed hydrolysis of the ester Saponification is the base-catalyzed hydrolysis of the ester bonds in a triglyceride.bonds in a triglyceride.
• We also discussed this reaction in Unit 4We also discussed this reaction in Unit 4
• This cleaves the esters back into carboxylic acids (fatty This cleaves the esters back into carboxylic acids (fatty acids) and an alcohol (glycerol).acids) and an alcohol (glycerol).
• Because the reaction is base-catalyzed, the base also Because the reaction is base-catalyzed, the base also reacts with the carboxylic acids to from carboxylate ionsreacts with the carboxylic acids to from carboxylate ions
• We saw this on an We saw this on an earlier slideearlier slide
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Reactions With Water (Unit 4)Reactions With Water (Unit 4)
Hydrolysis example:Hydrolysis example:• The base catalyzed hydrolysis of fats produces soap and The base catalyzed hydrolysis of fats produces soap and
glycerolglycerolC
O
O
C
O
O
C
O
OH
H
H
H
CH2
CH
CH2
3 H2O
OH-
FatFatFatFat
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Reactions With Water (Unit 4)Reactions With Water (Unit 4)
Hydrolysis example:Hydrolysis example:• The base catalyzed hydrolysis of fats produces soap and The base catalyzed hydrolysis of fats produces soap and
glycerolglycerol
SoapSoapSoapSoap GlycerolGlycerolGlycerolGlycerol
3 H2O
OH-
C
O
O
C
O
O
C
O
OH
H
H
H
CH2
CH
CH2
HO
HO
HO
+
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
Phospholipids and Glycolipids are the stuff that biological Phospholipids and Glycolipids are the stuff that biological membranes are made of.membranes are made of.
• Like the soaps, these molecules are highly aphipathic, and Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes when mixed with water spontaneously form membranes that are described as that are described as lipid bilayerslipid bilayers..
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
Phospholipids and GlycolipidsPhospholipids and Glycolipids
Phospholipids and Glycolipids are the stuff that biological Phospholipids and Glycolipids are the stuff that biological membranes are made of.membranes are made of.
• Like the soaps, these molecules are highly aphipathic, and Like the soaps, these molecules are highly aphipathic, and when mixed with water spontaneously form membranes when mixed with water spontaneously form membranes that are described as that are described as lipid bilayerslipid bilayers..
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• There a are two types of phospholipidsThere a are two types of phospholipids
• GlycerophospholipidsGlycerophospholipids
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• There a are two types of phospholipidsThere a are two types of phospholipids
• SphingolipidsSphingolipids
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• The Glycerophospholipids have a structure similar to The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a triglycerides, with one of the fatty acids replaced with a phosphate.phosphate.
There is usually There is usually an additional an additional alcohol attached alcohol attached to the other side to the other side of the phosphateof the phosphate
There is usually There is usually an additional an additional alcohol attached alcohol attached to the other side to the other side of the phosphateof the phosphate
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• The Glycerophospholipids have a structure similar to The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a triglycerides, with one of the fatty acids replaced with a phosphate.phosphate.
phosphoesterphosphoesterbondsbonds
phosphoesterphosphoesterbondsbonds
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• The Glycerophospholipids have a structure similar to The Glycerophospholipids have a structure similar to triglycerides, with one of the fatty acids replaced with a triglycerides, with one of the fatty acids replaced with a phosphate.phosphate.
““Phosphotidyl-”Phosphotidyl-”refers to everythingrefers to everything
but the Xbut the X
““Phosphotidyl-”Phosphotidyl-”refers to everythingrefers to everything
but the Xbut the X
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• Phospholipids are used commercially as Phospholipids are used commercially as emulsifying emulsifying agentsagents..
• An emulsifying agent stabilizes an emulsion.An emulsifying agent stabilizes an emulsion.
• An emulsion is a colloidal suspension of one liquid in another.An emulsion is a colloidal suspension of one liquid in another.
‣ An example is mayonnaise, which is a colloidal suspension of oil and An example is mayonnaise, which is a colloidal suspension of oil and water.water.
• LecithinLecithin, which is another name for the phospholipid , which is another name for the phospholipid phosphotidylcholine, is used as an emulsifying agent in phosphotidylcholine, is used as an emulsifying agent in mayonnaise and other prepared foods. mayonnaise and other prepared foods.
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• The sphingolipids function similarly to the The sphingolipids function similarly to the glycerophospholipids, but structurally they are different.glycerophospholipids, but structurally they are different.
• There is not glycerol coreThere is not glycerol core
• The glycerol and one of the fatty acids found in glycerophospholipids The glycerol and one of the fatty acids found in glycerophospholipids is replaced with a molecule called is replaced with a molecule called sphingosinesphingosine..
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Phospholipids and GlycolipidsPhospholipids and Glycolipids
PhosphospholipidsPhosphospholipids
• The sphingolipids are found in the myelin membranes that The sphingolipids are found in the myelin membranes that insulate the nerve cells.insulate the nerve cells.
• Some sphingolipids use sugars for the alcohol portion of Some sphingolipids use sugars for the alcohol portion of the moleculethe molecule
• These are called These are called glycolipidsglycolipids..
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SteroidsSteroids
Steroids are a type of lipid that is not derived form a fatty Steroids are a type of lipid that is not derived form a fatty acid.acid.• They are based instead on a system of five cycloalkane They are based instead on a system of five cycloalkane
rings that are fused together.rings that are fused together.
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SteroidsSteroids
Steroids are a type of lipid that is not derived form a fatty Steroids are a type of lipid that is not derived form a fatty acid.acid.• They are based instead on a system of five cycloalkane They are based instead on a system of five cycloalkane
rings that are fused together.rings that are fused together.
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SteroidsSteroids
Cholesterol is the steroid that used as the starting point for Cholesterol is the steroid that used as the starting point for the synthesis of other steroids.the synthesis of other steroids.
Note the fused ring Note the fused ring systemsystem
Note the fused ring Note the fused ring systemsystem
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SteroidsSteroids
• Cholesterol is only found in animalsCholesterol is only found in animals• Besides being used to synthesize the other steroids, Besides being used to synthesize the other steroids,
cholesterol is dissolved in membranes to keep them fluid.cholesterol is dissolved in membranes to keep them fluid.• Plants use the alternative strategy of using polyunsaturated fatty Plants use the alternative strategy of using polyunsaturated fatty
acids to make their phospholipids.acids to make their phospholipids.
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LipoproteinsLipoproteins
LipoproteinsLipoproteins are used to transport the are used to transport the water insoluble lipids such as water insoluble lipids such as triglycerides, phospholipids and triglycerides, phospholipids and cholesterol, in the blood.cholesterol, in the blood.• Lipoproteins contain lipids and Lipoproteins contain lipids and
proteins.proteins.• They include:They include:
• ChylomicronsChylomicrons transport primarily transport primarily triglycerides from the digestive track.triglycerides from the digestive track.
• LDLsLDLs (low density lipoproteins) transport (low density lipoproteins) transport cholesterol, triglycerides and cholesterol, triglycerides and phospholipids from the liver to other phospholipids from the liver to other tissues.tissues.
• HDLsHDLs (high density lipoproteins) transport (high density lipoproteins) transport cholesterol and phospholipids back to the cholesterol and phospholipids back to the liver.liver.
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LipoproteinsLipoproteins
The HDL and LDL levels in the blood can be used to assess The HDL and LDL levels in the blood can be used to assess ones risk for atherosclerosis.ones risk for atherosclerosis.
• High levels of HDL is considered goodHigh levels of HDL is considered good
• This is why HDL is sometimes referred to as “good cholesterol”This is why HDL is sometimes referred to as “good cholesterol”
• > 40 mg/dL is good.> 40 mg/dL is good.
• High levels of LDL is considered badHigh levels of LDL is considered bad
• This is why LDL is sometimes referred to as “bad cholesterol”This is why LDL is sometimes referred to as “bad cholesterol”
• > 100 mg/dL is bad.> 100 mg/dL is bad.
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EicosanoidsEicosanoids
Eicosanoids are derived from arachidonic acid:Eicosanoids are derived from arachidonic acid:
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MembranesMembranes
Fluid mosaic modelFluid mosaic model
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MembranesMembranes
Transport across membranesTransport across membranes
