Chem 150 Unit 5 - Biological Molecules I Lipids

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Chem 150Unit 5 - Biological Molecules ILipids

• Like organic molecules, biological molecules are
  grouped into families. There are four major
  families of biological molecules, including
  proteins, nucleic acids, carbohydrates, and
  lipids. The lipids are the subject of this unit.
  Of these four families, the lipids are the
  structurally the most diverse. This is because
  unlike members of the other three families,
  members of this families do no share a common
  structural feature, but rather share a common
  physical property the are hydrophobic.

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Introduction

• Lipids are hydrophobic, nonpolar molelcules.
• They are soluble in nonpolar solvent.
• They are insoluble in polar solvents, such as
  water
• They are isolated from the other biological
  molecules by extracting them with nonpolar
  solvents.

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Introduction

• The types of lipids that we will look at include.
• Fatty Acids
• In the carboxylic acid family
• Waxes
• Fatty Acids Alcohols
• Triglycerides
• 3 Fatty acids glycerol
• Phospholipids and glycolipides
• 2 fatty acids glycerol phosphate X
• Steroids
• Derivatives of cholesterol
• Eicosanoids
• Derivatives of the Fatty acid arachidonic acid
• Membranes
• Formed from phospholipids and glycolipids

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Fatty Acids

• Melting points for saturated fatty acids

Melting Temperature C
No. of Carbons
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Fatty Acids

• Some fatty acids contain double bonds
• unsaturated
• monounsaturated
• polyunsaturated
• polyunsaturated

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Fatty Acids

• The common fatty acids found in biological
  systems are shown in Table 8.1 of Raymond.

Text
Linolenic acid is one of the omega-3 fatty acids.
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Fatty Acids

• Normally the double bonds are cis
• This lowers the melting points for fatty acids
  containing double bonds.

Melting Temperature C
No. of Double Bonds
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Fatty Acids

• The cis double bonds produce kinks, which disrupt
  the London forces by preventing the tails from
  packing close to one another.

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Fatty Acids

• As acids, the carboxylic acid group in fatty
  acids can react with a base to produce a
  carboxylate ion
• By donating its proton (H) to the base the fatty
  acid becomes negatively charged.
• We will talk more about acids and bases in Unit 6

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Fatty Acids

• The negative charge makes the polar head portion
  of the the fatty acid even more more polar and
  hydrophilic.

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Fatty Acids

• The salts of fatty acids are also called soaps,
  and are considered amphipathic, meaning they have
  a part that is very hydrophobic along with a part
  that is very hydrophilic.
• In Unit 3 we discussed how amphipathic molecules
  form interesting structures when exposed to water.

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Biochemical Compounds Their Interactions with
Water (Unit 3)

• When placed in water, amphipathic molecules, form
  structures, such as micelles, which attempt to
  address the conflict.

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Fatty Acids

• The salts of fatty acids are also called soaps,
  and are considered amphipathic, meaning they have
  a part that is very hydrophobic along with a part
  that is very hydrophilic.
• In Unit 3 we discussed how amphipathic molecules
  form interesting structures when exposed to water.

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Waxes

• Waxes are made by combining fatty acids with long
  chain alcohols.
• In Unit 2 we discussed how carboxylic acids react
  with alcohols to from esters.

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Alcohols, Carboxylic Acids Esters (Unit 2)

• We look now at three families that are
  distinguished by a functional group that contains
  the element oxygen.
• Esters
• Chemically, esters can be synthesize by reacting
  a carboxylic acid with and alcohol

Ethyl propanoate
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Waxes

• Waxes are very hydrophobic and are used by plants
  and animals for protective, water-proof coatings

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Questions

• Draw the skeletal structures for the products
  formed when beeswax undergoes base-catalzyed
  hydrolysis (saponification).

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Reactions Involving Water (Unit 4)

• Hydrolysis
• Hydrolysis can also be catalyzed using a base
  (OH-).
• 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 carboxylic acid to produce a carboxylate
  ion.
• The base catalyzed hydrolysis of esters is also
  called saponification
• We will be discussing acids and bases in Unit 6

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Triglycerides

• Triglycerides are a storage form of fatty acids
  in mammals.
• Often when blood tests are done, they measure
  your triglycyeride levels.
• High triglyceride levels in the blood are a risk
  indicator for artherosclerosis.

American Heart Association
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Triglycerides

• Triglycerides are a combination of three 3 fatty
  acid molecules with a glycerol molecule.

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Triglycerides

• Glycerol, which is also called glycerin, is an
  alcohol with three hydroxyl groups.
• As with the waxes, the fatty acids can react with
  the hydroxyl groups to form esters.
• Since there are three hydroxyl groups, three
  fatty acids can react to form three esters.

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Triglycerides

• For triglycerides, all three hydroxyls of the
  glycerol have a fatty acid residue attached to it.

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Figure 8.6 from Raymond
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Triglycerides

• Just as with fatty acids, where the presence of
  cis double bonds lower the melting points,
  triglycerides made from unsaturated fatty acids
  have lower melting points than those made from
  saturated fatty acids.
• Triglycerides from animals tend to have a higher
  proportion of saturated fatty acids.
• Most are solids at room temperature and are
  called fats.
• Examples include butter, lard and bacon grease
• Triglycerides from plants tend to have a higher
  proportion of unsaturated fatty acids.
• Most are liquids at room temperature and are
  called oils.
• Examples include corn oil, canola oil, peanut
  oil and olive oil.

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Triglycerides

• Triglycerides as primarily used as a form of
  stored energy.
• This is why when you eat more than you need to
  meet your energy requirements, the excess energy
  is stored in the form of fat.
• Fat can store almost twice as much energy per
  gram as carbohydrates and proteins
• In mammals the fats are stored in the adipose
  tissue.
• Adipose tissue also functions to protect organs
  from shock and cold.

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Triglycerides

• Reactions that involve triglycerides include
• Hydrogenation
• Oxidation
• Base-catalyzed hydrolysis (saponification)

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Triglycerides

• Hydrogenation of triglycerides
• This is the same reaction that we saw in Unit 4
  with the hydrogenation of alkenes.
• Unsaturated fats and oils contain alkenes and can
  be hydrogenated to produce saturated fats.
• Commercially, vegetable oils are often
  hydrogenated to produce a solid product that has
  better qualities for making baked goods.
• Animal fats, such as butter and lard, which are
  naturally saturated, can also be used, but unlike
  the vegetable oils, they come with cholesterol,
  which is undesirable for health reasons.

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Oxidation and Reduction (Unit 4)

• Hydrogenation
• Another type of oxidation/reduction reaction is
  the hydrogenation reaction
• In this example, an alkene is reduced to an
  alkane.
• This is considered reduction, because the
  hydrogen is bringing in additional electrons to
  the molecule.
• The alkane that is produced in this reaction is
  considered saturated because it can no longer
  absorb any more hydrogen atoms.

saturated
unsaturated
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Triglycerides

• Hydrogenation of triglycerides
• This is the same reaction that we saw in Unit 4
  with the hydrogenation of alkenes.
• Unsaturated fats and oils contain alkenes and can
  be hydrogenated to produce saturated fats.
• Commercially, vegetable oils are often
  hydrogenated to produce a solid product that has
  better qualities for making baked goods.
• Animal fats, such as butter and lard, which are
  naturally saturated, can also be used in baking,
  but unlike the vegetable oils, they come with
  cholesterol, which is undesirable for health
  reasons.

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Triglycerides

• Hydrogenation of triglycerides
• Total hydrogenation

liquid
solid
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Transport of fats
VLDL moves triglycerides from liver to tissues.
LDL transfers cholesterol to tissues from liver.
HDL carries cholesterol from tissues to liver.
Monoglycerides and fatty acids are absorbed
by intestines - transported as chylomicrons in
lymph system to blood.-Fat Blocker-Xenical
(orlistat)
Dietary fat
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Fun Topic ! Fake Fats
Side effects?
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Triglycerides

• Hydrogenation of triglycerides
• Partial hydrogenation

liquid
solid
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Triglycerides

• Hydrogenation of triglycerides
• Partial hydrogenation cab produce trans fats.
• Trans fats have been found to lower your HDL
  (Good cholesterol) levels.

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Triglycerides

• Saturated vs Unsaturated Fats

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Triglycerides

• Saturated vs Unsaturated Fats

Fat (Triacylglyceride)
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Triglycerides

• Oxidation of triglycerides
• Unsaturated triglycerides can react with oxygen
  to produce small change fatty acids another small
  molecules.
• These often do not smell very good
• This is what happens when butter goes rancid.
• This makes solid fats and oils more stable than
  liquid oils and is why the solid fats are
  preferred for deep frying.

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Triglycerides

• Oxidation of triglycerides

These stink !
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Triglycerides

• Saponification of triglycerides
• Saponification is the base-catalyzed hydrolysis
  of the ester bonds in a triglyceride.
• We also discussed this reaction in Unit 4
• This cleaves the esters back into carboxylic
  acids (fatty acids) and an alcohol (glycerol).
• Because the reaction is base-catalyzed, the base
  also reacts with the carboxylic acids to from
  carboxylate ions
• We saw this on an earlier slide

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Reactions With Water (Unit 4)

• Hydrolysis example
• The base catalyzed hydrolysis of fats produces
  soap and glycerol

Fat
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Reactions With Water (Unit 4)

• Hydrolysis example
• The base catalyzed hydrolysis of fats produces
  soap and glycerol

Soap
Glycerol
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Phospholipids and Glycolipids

• Phospholipids and Glycolipids are the stuff that
  biological membranes are made of.
• Like the soaps, these molecules are highly
  aphipathic, and when mixed with water
  spontaneously form membranes that are described
  as lipid bilayers.

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Phospholipids and Glycolipids

• Phospholipids and Glycolipids are the stuff that
  biological membranes are made of.
• Like the soaps, these molecules are highly
  aphipathic, and when mixed with water
  spontaneously form membranes that are described
  as lipid bilayers.

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Phospholipids and Glycolipids

• Phosphospholipids
• There a are two types of phospholipids
• Glycerophospholipids

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Phospholipids and Glycolipids

• Phosphospholipids
• There a are two types of phospholipids
• Sphingolipids

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Phospholipids and Glycolipids

• Phosphospholipids
• The Glycerophospholipids have a structure similar
  to triglycerides, with one of the fatty acids
  replaced with a phosphate.

There is usually an additional alcohol attached
to the other side of the phosphate
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Phospholipids and Glycolipids

• Phosphospholipids
• The Glycerophospholipids have a structure similar
  to triglycerides, with one of the fatty acids
  replaced with a phosphate.

phosphoester bonds
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Phospholipids and Glycolipids

• Phosphospholipids
• The Glycerophospholipids have a structure similar
  to triglycerides, with one of the fatty acids
  replaced with a phosphate.

Phosphotidyl- refers to everything but the X
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Phospholipids and Glycolipids

• Phosphospholipids
• Phospholipids are used commercially as
  emulsifying agents.
• An emulsifying agent stabilizes an emulsion.
• An emulsion is a colloidal suspension of one
  liquid in another.
• An example is mayonnaise, which is a colloidal
  suspension of oil and water.
• Lecithin, which is another name for the
  phospholipid phosphotidylcholine, is used as an
  emulsifying agent in mayonnaise and other
  prepared foods.

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Phospholipids and Glycolipids

• Phosphospholipids
• The sphingolipids function similarly to the
  glycerophospholipids, but structurally they are
  different.
• There is not glycerol core
• The glycerol and one of the fatty acids found in
  glycerophospholipids is replaced with a molecule
  called sphingosine.

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Phospholipids and Glycolipids

• Phosphospholipids
• The sphingolipids are found in the myelin
  membranes that insulate the nerve cells.
• Some sphingolipids use sugars for the alcohol
  portion of the molecule
• These are called glycolipids.

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Steroids

• Steroids are a type of lipid that is not derived
  form a fatty acid.
• They are based instead on a system of five
  cycloalkane rings that are fused together.

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Steroids

• Steroids are a type of lipid that is not derived
  form a fatty acid.
• They are based instead on a system of five
  cycloalkane rings that are fused together.

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Steroids

• Cholesterol is the steroid that used as the
  starting point for the synthesis of other
  steroids.

Note the fused ring system
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Steroids

• Cholesterol is only found in animals
• Besides being used to synthesize the other
  steroids, cholesterol is dissolved in membranes
  to keep them fluid.
• Plants use the alternative strategy of using
  polyunsaturated fatty acids to make their
  phospholipids.

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Lipoproteins

• Lipoproteins are used to transport the water
  insoluble lipids such as triglycerides,
  phospholipids and cholesterol, in the blood.
• Lipoproteins contain lipids and proteins.
• They include
• Chylomicrons transport primarily triglycerides
  from the digestive track.
• LDLs (low density lipoproteins) transport
  cholesterol, triglycerides and phospholipids from
  the liver to other tissues.
• HDLs (high density lipoproteins) transport
  cholesterol and phospholipids back to the liver.

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Lipoproteins

• The HDL and LDL levels in the blood can be used
  to assess ones risk for atherosclerosis.
• High levels of HDL is considered good
• This is why HDL is sometimes referred to as good
  cholesterol
• gt 40 mg/dL is good.
• High levels of LDL is considered bad
• This is why LDL is sometimes referred to as bad
  cholesterol
• gt 100 mg/dL is bad.

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Eicosanoids

• Eicosanoids are derived from arachidonic acid

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Membranes

• Fluid mosaic model

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Membranes

• Transport across membranes

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The End