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.
1. FATTY ACIDS – LIPID BUILDING BLOCKS
2. TRIACYLGLYCERIDES & PHOSPHOLIPIDS
3. SPHINGOMYELINS (NOT VERY DIFFICULT)
4. CHOLESTEROL & FRIENDS (STEROIDS)
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.
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.
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.
SOME EXAMPLES OF LIPIDS:
This lipid is a fat.
WHY ARE LIPIDS IMPORTANT?
1. They are a significant source of fuel/ energy
2. They form borders for cells and within cells
3. They are sources of hormones & vitamins.
TRIACYLGLYEROLS
HEART TISSUE
OTHER TISSUES (STARVATION)
INSULIN DEPENDENT TISSUES
(DIABETES)
PHOSPHOLIPIDS
CHOLESTEROL
FORM/ MAINTAIN PLASMA
MEMBRANES AND SUB-CELLULAR
ORGANELLE BOUNDARIES
t
CHOLESTEROL
PRECURSOR FOR MANY
HORMONES
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.
d+
d+
ENERGETICALLY,
LIPIDS ARE STABLE IN
NON-POLAR SOLVENTS
dAND THEY ARE CALLED
“HYDROPHOBIC” – WATER HATING COMPOUNDS.
H
H
O
OF COURSE, THERE ARE EXCEPTIONS. SOME LIPIDS HAVE
A PORTION OF THEIR COMPOSITION THAT IS
COMPATIBLE WITH WATER (CHARGED REGIONS). SUCH
LIPIDS ARE CALLED “AMPHIPATHIC” – DUAL ROLES.
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. This is energetically favorable
for the polar solvent.
It helps if the non-polar compound
(such as a lipid) has some hydrophilic
region(s).
The micelle structure to the right 
is composed of fatty acids in which
a) the alkyl groups are buried inward
b) the carboxyl groups interact with
the polar water molecules.
What if there are no hydrophilic regions?
TWO NON-POLAR SOLVENTS ARE SHOWN
HERE:
CH3
CH3
HEPTANE
CYCLOHEXANE
TWO PARTIALLY POLAR LIPIDS ARE SHOWN HERE:
POLAR ENDS
PALMITIC ACID
OLEIC ACID
Fatty acids: lipid building blocks
• 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+
DODECANOIC ACID or LAURIC ACID
Greek = 12 (dodekanos = dodekanos)
Latin = laurel plant (laurus)
FATTY ACID FACTS:
• FA have both IUPAC (systematic) &
common names.
• FA partially deionize.
• Most biological FA are 12-24 carbons long.
• FA are either completely saturated or have
one or more double bonds.
•  carbon length -  melting point
•  unsaturation -  melting point
Here are the effects of saturation and carbon
lengths on melting points of fatty acids
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 at C3 from the
methyl group (opposite of the carboxyl group)
This is an example of an omega-3 fatty acid.
Commercial hydrogenation converts FAs in the
cis configuration (shown on the left) into saturated
FA. However, side reactions also 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)
SATURATED VS. UNSATURATED FA
• There is a wide variety of FA consumed in our diets and
it depends on the source of the lipids.
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.
Analysis of Fatty Acids:
Treat (b) and
(c) With NaOH
and methanol
to produce
fatty acyl
methyl esters
(transesterification).
Process at (e) or (f).
STORED FAT: TRIACYLGLYCEROLS
(TGs)
TAG FACTS
• Most of the FAs in TAGs are of mixed
chain length and degree of saturation
(important for membrane properties).
• The energy obtained by metabolic
oxidation of TAGs is ~2.2x that of proteins
and carbohydrates.
• TAGs are an important temperature
insulator for animals.
SAPONIFICATION
(FAT HYDROLYSIS)
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.
STRUCTURAL FORMS OF
LIPIDS
• There are three types of lipids that are
used to form tissue structures
(membranes):
• GLYCEROPHOSPHOLIPIDS
• SPHINGOLIPIDS
• STEROIDS (CHOLESTEROL)
GLYCEROPHOSPHOLIPIDS
Glycerophospholipids (phospholipids) are a
variation of TGs, but they substitute a polar
headgroup for one of the FA parts. Shown
below is phosphatidic acid:
TYPES AND NATURE OF HEAD GROUPS:
Example – phosphatidyl choline
The choline group, shown in the box, is one type of
phospholipid head group that has a positive charge
located on the N. This groups interacts with water
on either side of a membrane.
OTHER POLAR HEAD GROUPS:
GLYCEROPHOSPHOLIPIDS ARE GLYCEROL*
UNITS TO WHICH ARE ESTERIFIED:
2 FATTY ACIDS AND ONE POLAR HEAD UNIT
THE FATTY ACIDS ARE COMMONLY MIXED –
ONE SATURATED AND ONE UNSATURATED
THE HEAD UNITS CONSIST OF SIX COMMON
TYPES – CHOLINE AND ETHANOLAMINE ARE
TWO OF THE MOST COMMON TYPES.
*GLYCEROL IS A “HINGE MOLECULE”
GLYCEROPHOSPHOLIPIDS (PL) FOR
MOST OF US SERVE AS MEMBRANE
COMPONENTS PRIMARILY AND AS
FUEL SECONDARILY.
THE POLAR BEAR USES PL AS:
1) AN INSULATOR
2) A FUEL
3) A SOURCE OF WATER:
PL  PHG + FA  FA (- 2C)  HOH
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?
A CLASS OF LIPIDS WHOSE
STRUCTURE PERPLEXED
INVESTIGATORS WERE
KNOWN AS SPHINGOLIPIDS
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SPHINGOLIPIDS USE SPHINGOSINE AS THEIR
HINGE MOLECULE INSTEAD OF GLYCEROL.
Examples of some sphingolipids:
WHERE AND WHY ARE
SPHINGOLIPIDS PRESENT?
1. ARE OFTEN FOUND IN NERVOUS
MEMBRANES OF HIGHER ANIMALS.
2. SPHINGOMYELIN IS ALSO FOUND IN
MUSCLE MEMBRANES.
3. GLYCOSPHINGOLIPDS ARE ALSO
IMMUNOMARKERS FOR CELLS.
A NOTE TO CONSIDER:
THE DEGRADATION 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 (GM2) IS ONLY PARTIALLY DEGRADED
DUE TO THE DEFICIENCY OF THE ENZYME: HEXOSAMINIDASE A. THE EXCESS LIPID CAUSES MENTAL
RETARDATION AND EVENTUALLY DEATH.
ISOPRENE & CHOLESTEROL
• A final consideration with lipids and
membranes is with the steroid known as
cholesterol (no fatty acid components
here).
• Cholesterol is synthesized from terpene
units known as isoprene:
ISOPRENE IS A DANGEROUS
LIPID:
1.
2.
3.
4.
IT IS A COLORLESS LIQUID
HIGHLY INFLAMMABLE
OBTAINED FROM REFINING OIL
STARTING MATERIAL FOR
MAKING SYNTHETIC RUBBER
BUT, IN THE BODY –
IT IS MADE FROM acetyl CoA
SOME COMMONLY KNOWN TERPENES:
CHOLESTEROL
1. is a steroid - a terpenoid lipid with four
fused rings.
2. is the starting molecule for hormone
synthesis.
3. An important component of plasma
membranes, some intracellular
organelles, and blood lipoprotein
complexes.
2
1
3
1. The hydroxyl group on cholesterol
is often esterified to fatty acids to
make cholesteryl esters.
2. The methyl groups on cholesterol
can be substituted with other
groups (e. g., fluorine) and
profoundly change the properties
of the molecule.
3. The tail of the cholesterol molecule
is often shortened and substituted
to form hormones.
SUMMARY
• FATTY ACIDS ARE THE BUILDING BLOCKS OF
MOST BIOLOGICAL LIPIDS.
• FATS ARE STORED AS TRIACYLGLYERIDES.
• LIPIDS ARE INCORPORATED INTO
MEMBRANES AS PHOSPHOLIPIDS,
SPHINGOMYELINS AND CHOLESTEROL.
• THE PROPERTIES OF EACH OF THESE
CLASSES OF LIPIDS DETERMINES THEIR
BIOLOGICAL USE.
IMPORTANT THINGS TO STUDY FROM THIS LECTURE:
1.
2.
3.
4.
5.
6.
WHAT IS THE DIFFERENCE BETWEEN FAT AND LIPIDS?
WHAT ARE THE BIOLOGICAL USES OF LIPIDS?
ARE LIPIDS NON-POLAR? WHAT DOES THAT MEAN?
WHAT GENERAL STRUCTURAL PROPERTIES DO FATTY ACIDS HAVE?
HOW ARE THEY NAMED?
WHAT PROPERTIES DO SATURATION/UNSATURATION GIVE TO FATTY
ACIDS? WHAT ARE TRANS FATTY ACIDS?
7. IN REFERENCE TO 6. – WHAT KINDS OF FATTY ACIDS ARE IMPORTANT
IN THE DIET?
8. HOW CAN FATTY ACIDS BE ANALYZED?
9. WHAT IS SAPONIFICATION? HOW ARE FATS METABOLIZED IN TISSUES
FOR EXAMPLE – TO PRODUCE STORAGE FORMS IN CELLS?
10. CAN YOU DISTINGUISH BETWEEN GLYCEROPHOSPHOLIPID AND
SPHINGOLIPID STRUCTURES? WHERE DO THESE LIPIDS OCCUR?
11. CAN YOU GIVE SOME BASIC STRUCTURAL PROPERTIES OF
CHOLESTEROL AND WHERE IT IS LOCATED IN THE BODY?