Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
Lipids
Slide #1- Lipids
 It is almost impossible to watch TV ads without some company talking about fats and
dieting. We’re familiar with that, but we still crave the foods that contain fats and still
know very little about them.
Slide #2- What are we going to be covering today?
 Fatty acids- Lipid building blocks
 Triacylglycerides and Phospholipids
 Sphinomyelins (not very difficult)
 Cholesterol and Friends (Steriods)
Slide #3- Essential Information
 Fats are lipids, but NOT ALL LIPIDS ARE FATS. Both substances are soluble in
non-polar solvents -- like benzene and xylene (liquids used in organic chemistry).
However, the terms lipids and fats have different meanings even though they are both
soluble in these non polar solvents.
 Fats are esters formed from fatty acids and the compound glycerol. Animals use fats
for energy storage and insulation.
 Lipids are compounds soluble in a non-polar solvents, but they don’t have to be esters
Slide #4
 So a lipid could include stuff like gasoline or jet engine fuel (specially formulated
kerosene)
 Or even be in that material in our bodies that the weight reduction people call
“cellulite”- tissue composed of cells full of triacylglerols, a type of fat
 We have to be careful how the terms are used. All the compounds used in this course
are all accurately called lipids.
Slide #5- Some Examples of Lipids
 Top left hand side- Cholesterol- bad name over the years but you can not live without
it
 Bottom left hand side- Warfarin (Coumadin)- blood thinner. Also used as a poison to
kill rodents. If the rodent ingests it he will die because he bleeds out- used quite
commonly.
 Right- Tristearin- this is a fat.- triacylglycerol or triglyceride- has l3 long tail like
structures that are part of a fatty acid and on the top is a glycerol molecule
Slide #6- Why are lipids important?
1. They are a significant source of fuel/ energy.- Lipids are more of a source of energy
than proteins or carbohydrates.
2. They form borders for cells and within cells
3. They are sources of hormones & vitamins.
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Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
Slide #7- Some Examples
 Triacylglycerols-Important fuel for heart tissue
-Under starvation they can nourish other tissues particularly in diabetes- insulin
dependent tissues no longer to absorb carbohydrates; use triacylglycerides as a fuel
substitute; however causes problems after awhile.
 Phospholids and Cholesterol-Form and maintain plasma membranes
-Sub-cellular organelle boundaries
-Cholesterol itself which is used for many types of hormones.
Slide #8- Lipid Solubility Characteristics
 It goes without saying that lipids are soluble in non-polar solvents. That is, there is
no partial charge in any part of a lipid solvent such as is found in water.
 In water, the oxygen molecule is electron withdrawing, it tends to pull electrons away
from the hydrogen. The hydrogen atoms attain a positive charge and the oxygen a
negative charge- Polarity
 Energetically, Lipids are stable in non-polar solvents and are called hydrophobicwater hating compounds
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Of course, there are exceptions. Some lipids have a portion of their composition that is
compatible with water. For example: Fatty acid- one end of the molecule has a carboxyl
group partially ionized (charged), rest of molecule has no charge.
Fatty acid with long chain- not very soluble in water
Short chain fatty acids- very soluble in water. Example vinegar- 5% acetic acid, completely
soluble
Most lipids are not very soluble in water.
amphipathic- dual roles- polar end and non-polar end
Slide #9- What exactly is a hydrophobic bond?
 It is not a true bond, but an association of non-polar compounds made to minimize
their contact with a polar solvent (usually water). This is energetically favorable for
the polar solvent.
 It helps if the non-polar compound (such as a lipid) has some hydrophilic region(s).
 See diagram- Series of fatty acids in water- non polar ends start to associate in a
structure called a micelle
 The micelle structure is composed of fatty acids in which
a) the alkyl groups are buried inward
b) the carboxyl groups (charged) interact with
the polar water molecules.
 What if there are no hydrophilic regions?
Suppose you had a lipid in water and a drop of oil fell in. What would occur? Contact
between lipid and water is minimized. Take a separatory funnel and you have water and
lipid and shake it, you get a phase separation- you have minimal contact between the
water molecules and the lipid itself. Energetically favorable for the polar solvent.
Slide #102
Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
 Non-polar solvents
 Partially polar lipids- region of non-polarity is the alkyl groups and the carboxylic
acid groups
Slide #11- Fatty acids: lipid building blocks
 Fatty acids are lipid building blocks of most lipids even cholesterol (fatty acids will
for esters with the cholesterol itself)
 Fatty acids have two parts: a hydrocarbon tail and a carboxylic head
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COO- H+
 Fatty acid above: DODECANOIC ACID (systematic name) or LAURIC
ACID(common name- source from where first observed)
 Greek = 12 (dodekanos = dodekanos)
 Latin = laurel plant (laurus)
Slide #12
 Examples of names:
 Saturated fatty acid- Palmitic acid and Stearic acid
 Can take fatty acids and remove hydrogens and get double bonds
 Monosaturated- one double bond- Oleic acid
 Diunsaturated- 2 double bonds- Linoleic acid
 Polyunsaturated- 3 or more double bonds- alpha-Linolenic acid (3) and Arachidonic
acid (4) (Arachinoid- spider)
Slide #13- Fatty acid facts
 FA have both IUPAC (systematic) & common names.
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FA partially deionize.- why some can be used as buffers
Most biological FA are 12-24 carbons long- up to about 36
FA are either completely saturated or have one or more double bonds.
 carbon length -  melting point
 unsaturation -  melting point
Slide #14
 Some examples- see graph
 Important for cell membranes- if you increase the degree of unsaturation (number of
double bonds) in fatty acids, you increase randomness or disorder of a fatty acid in a
membrane; thus, making it more fluid.
 Cell membranes will be a mixture of degrees of saturation and unsaturation.
Slide #15- Some Shorthand Naming
 Short-hand methods for naming FA begin with either the carboxylic acid end or the
methyl end of the molecule:
 lauric acid = 12:0; oleic acid = 18:1
 linolenic acid = 18:3 D9,12,15 (This is also an w-3 fatty acid)
18:3 indicates an 18C fatty acid with three double bonds;
D9,12,15 shows the positions of the double bonds; and w-3 states the double bond begins
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Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
at C3 from the methyl group (opposite of the carboxyl group)
Slide #16
 Look at linolenic acid.
Slide #17
 Commercial hydrogenation converts FA in the cis configuration (shown on the left)
into saturated FA. However, side reactions produce trans FA (shown on the right). Trans
FA increase LDL* lipids in the body that cause a buildup of arterial lipid deposits leading
to atherosclerosis. *low density lipoprotein (containing so called “bad” cholesterol)
Slide #18- Saturated vs. Unsaturated FA
 See table
 There is a wide variety of FA consumed in our diets and it depends on the source of
the lipids.
 Saturated FA- high in beef
 Whole milk- high palmitic and stearic acid
 Want to have more unsaturated than saturated fat in diet.
Slide #19
 There are two issues, then, concerning the consumption of FA in the diet:
1.
excessive intake of saturated FA (beef and butter as examples)
2.
excessive intake of trans-FA (margarine made by hydrogenation)
 Some oils that tend to be low in saturated and trans-FA are canola, olive and flax
seed.
Slide #20- Analysis of Fatty Acids:
 Know this!
1. Take tissue (example is a piece of liver) and homogenize in
chloroform/methanol/H2O.
2. Put extract in separatory funnel and get two separate phases.
3. Analyze each phase by either:
a. absorbtion chromotography- silicic acid in solvent
b. thin layer plate which contains silicic acid, and after you run a solvent and get
separation of different types of lipids.
 How do you get FA after you have made the separation? Treat (b) or (c) NaOH and
methanol to produce fatty acyl methyl esters (transesterfication). Purpose: to make
fatty acid derivatives that are easily volitized- can be converted into gas.
 Put on high performance liquid chromatography or a gas liquid chromatograph
converting these to gases.
 Gases will go through a series of coils and separate out. When get to the end of coil,
burned at a hydrogen flame which will send a signal to an apparatus which will print
out and get shorter chain at bottom and longer chains that have unsaturated
 Can tell what is there and the quantity.
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Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
Slide #21- Stored Fat: Triacylglycerols (TGs)
 adipocytes
 When consume lipids gastrointestinal system will convert them and break them down
to fatty acids, and transported to fat cells where they will be assembled into a TG
 Reaction occurs by acyl transferase; 3steps- each step puts one FA onto glycerol
molecule.
 Glycerol comes from glucose and is a biproduct in the EM pathway.
 TGs stored in small lipid bodies within the adipocyes.
Slide #22- TG Facts
 Most of the FAs in TGs are of mixed chain length and degree of saturation (important
for membrane properties).
 The energy obtained by metabolic oxidation of TGs is ~2.2x that of proteins and
carbohydrates. Under starvation, lipids are the main thing broken down.
 TGs are an important temperature insulator for animals.
Slide #23- Saponification (Fat Hydrolysis)
 Artificially: Treat TG with KOH or NaOH then heat and get glycerol and potassium
or sodium salt (Soap). Old days: ash and animal fat- soap
 Cells produce their own form of TG hydrolysis by using lipase enzymes to separate
FAs prior to transporting them and combining them into new lipids.
 Lipids constantly being broken down or separated from their parent compound, being
put into fat cells and transported to some location in body where they are needed to
make membranes.
Slide #24- Structural Forms of Lipids
There are three types of lipids that are used to form tissue structures (membranes):
•
Glycerophospholipids
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Sphingolipids
•
Steroids (Cholesterol)
Slide #25- Glycerophospholipids
 Glycerophospholipids (phospholipids) are a variation of TGs, but they substitute a
polar headgroup for one of the FA parts.
 See phosphatidic acid picture
 glycerol molecule is a hinge molecule
Slide #26- Types and Nature of Head Groups:
 Choline
 Ethanol amine
 Serine (an AA)
 Phosphoglycerol
 Diglycerol phosphate (Cardiolypin)
 Phosphtidylinositol (derivative of glucose)
 Polar head groups are unique.
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Fundamentals I
Lipids
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Whikehart
 Each head group has some degree of polarity.
Slide #27
 Glycerophospholipids are glycerol units to which are esterified: 2 Fatty acid and one
polar head unit.
 The fatty acids are commonly mixed- one unsaturated and one saturated
 The head units consist of 6 common types- choline and ethanolamine are two of the
most common types.
 Glycerol is a hinge molecule.
Slide #28
 Glycerophospholipids (PL) for most of us serve as membrane components primarily
and as fuel secondarily.
 The polar bear uses PL as:
1)
An insulator- gathers alot of fat
2)
A fuel- only eats 4 months of the year
3)
A source of H2O(cant drink):
PL  PHG + FA  FA (- 2C)  HOH
 Takes the PL and breaks it down into phospholipid and polar head group. Then it
takes the fatty acid and uses it to push through TCA cycle. Then onto oxidative
phosphorylation, where biproduct is H2O.
 Very efficient
Slide #29- Sphingolipids
THE RIDDLE OF THE SPHINX:
What goes on four feet in the morning;
Two feet in the afternoon; and
Three feet in the evening?
 See man, bird, lion which guarded the city of Theives; if a person wanted to get into
town they had to answer this riddle. If they did not answer it correctly, then they
were strangled. Lions will kill prey by strangulation. Story is Egyptian in origin, but
this is the Greek version. There are also oriental versions.
Sphingolipids- a class of lipids whose structure perplexed investigators
Slide #30
 Sphingolipids use sphingosine as their hinge molecule instead of glycerol.
 See sphingosine molecule
 Hybrid molecule
 Glycerol in the center
 On C2 there is an amino group
 One end is the remains of a fatty acid held together in a double bond that is now an
ester bond.
Slide #31- Examples of Sphingolipids
 Ceramide-bound to a FA through an amide bond on C2- wax compound
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Fundamentals I
Lipids
9/9/08 10-11am
Whikehart
 Cerebroside- add 1 sugar or carbohydrate group
 Sphingomyelin- bound to a choline group
 Gangliside- 2 or more sugar or carbohydrate groups
 Cerebroside and Gangliside are isolated from nervous tissue, and some from muscle
tissue.
Slide #32
1. Are often found in nervous membranes of higher animals.
2. Sphingomyelin is also found in muscle membranes.
3. Glycosphingolipids are also immunomarkers for cells-sugar molecules to identify cells
as “friend or foe“.
Slide #33- A Note to Consider
 The degredation of gangliosides occurs in lysosomes and is an important process. If a
deficiency in one or more degradative enzymes occurs there, then a disease known as
a metabolic storage disease may occur.
 An example is Tay-Sach’s Disease in which a ganglioside is only partially degraded
due to the deficiency of the enzyme: hexosaminidase A. The excess lipid causes
mental retardation and eventually death.
**Break**
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