LIPIDS
What are Lipids? Class of biomolecules that are all water
insoluble No defining characteristic except that all
of them share the same trait: non-polar Most common are fatty acids and esters
of fatty acids Functions
Energy Storage Cell membrane Thermal blanket and cushion Precursors of hormones
Fatty Acids Fatty acids consist of a hydrocarbon
chain with a carboxylic acid at one end. A 16-C fatty acid: CH3(CH2)14-COO-
Non-polar polar General Structure:
(CH2)nCH3 COOH
n is almost always even
n = 0 : CH3COOH n = 1 : propionic acid
Fatty Acids Double bonds in fatty acids usually have
the cis configuration. Most naturally occurring fatty acids have
an even number of carbon atoms. IUPAC naming:
COOH carbon as C1 Farthest carbon is ω Total carbons/# double bonds/Δdouble bond position
Fatty Acids Some fatty acids and their common names:
14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid;
18:1 cisD9 oleic acid 18:2 cisD9,12 linoleic acid 18:3 cisD9,12,15 a-linonenic acid 20:4 cisD5,8,11,14 arachidonic acid 20:5 cisD5,8,11,14,17 eicosapentaenoic acid (an omega-3)
Essential fatty acids ALA- ω-3 FA precursor for EPA and DHA LA – ω-6 FA precursor of AA
Fatty Acid Chemistry Peroxidation
a non-enzymatic reaction catalyzed by oxygen
may occur in tissues or in foods (spoilage) the hydroperoxide formed is very reactive
and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer)
principle is also used in drying oils (linseed, tung, walnut) to form hard films
Drying Oils: Application of Peroxidation
based on the ease of autoxidation and polymerization of oils (important in paints and varnishes)
the more unsaturation in the oil, the more likely the “drying” process Non-drying oils:
Castor, olive, peanut, rapeseed oils Semi-drying oils
Corn, sesame, cottonseed oils Drying oils
Soybean, sunflower, hemp, linseed, tung, oiticica oils
Fatty Acid Chemistry Transesterification
Acid-catalyzed exchange betweein R groups of esters
Frequently-used in polyester, methanolysis and biodiesel industries
Fatty Acid Chemistry Hydrogenation
Reduces double bonds on unsaturated fatty acids
Prevents oils from going rancid
Fatty Acid Chemistry Saponification
Base hydrolysis of triglycerides to produce fatty acid salts
High saponification number, shorter chain length
Soaps Types of soaps:
Sodium soap – ordinary hard soap Potassium soap – soft soap (shaving soaps are
potassium soaps of coconut and palm oils) Castile soap – sodium soap of olive oil Green soap – mixture of sodium and potassium
linseed oil Transparent soap – contains sucrose Floating soap – contains air Calcium and magnesium soaps are very poorly
water soluble (hard water contains calcium and magnesium salts –these insolubilize soaps)
Fatty Acid Chemistry Iodine Number
measures the degree of unsaturation in a given amount of fat or oil
the iodine number is the number of grams of iodine absorbed by 100 grams of fat Cottonseed oil: 103 –111 Olive oil: 79 – 88 Linseed oil: 175 –202
frequently used to determine adulteration of commercial lots of oils
HH I I
HHI2
Fatty Acid Chemistry Acetyl Number
the number of milligrams of KOH needed to neutralize the acetic acid of 1 g of acetylated fat
fatty acid
OH
acetic anhydridefatty acid
O C
O
CH3
fatty acid
OH
+
COOHH3C
titrate with standardizedKOH
acetylated fatty acid
Fatty Acid Chemistry Reichert-Meisl Number
measures the amount of volatile fatty acids (low MW and water soluble Fas)
the R-M number is the number of milliliters of 0.1N alkali required to neutralize the soluble fatty acids distilled from 5 Gm of fat
butter fat has a high R-M number Indicator of non-fat compounds in edible
fats, or volatile fatty acids
Fats and Oils fats are solids or semi solids oils are liquids melting points and boiling
points are not usually sharp (most fats/oils are mixtures)
when shaken with water, oils tend to emulsify
pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)
Waxes simple esters of fatty acids
(usually saturated with long chain monohydric alcohols) Beeswax – also includes some
free alcohol and fatty acids Spermaceti – contains cetyl
palmitate (from whale oil) –useful for pharmaceuticals (creams/ointments; tableting and granulation)
Carnauba wax – from a palm tree from brazil – a hard wax used on cars and boats
H3C (CH2)14 C
O
O CH2 (CH2)28-CH3
long chain alcoholfatty acid
Bee’s wax
Spermaceti source
Carnauba wax source
Glycerides Function
Storage of energy Cushions
O
OH
OH
R
O
O
OH
O
R
O
R
O
O
O
R
O
R
O
OR
O
MONOGLYCERIDE DIGLYCERIDE TRIGLYCERIDE
Triglycerides Esters of fatty acids and glycerol Constituent of fats and oils
Phosphoglycerides aka glycerophospholipids Major constituent of cell
membranes Structure
Glycerol backbone with esterifies fatty acids at C1 and C2
Fatty acids are usually non-identical
Phosphate group attached to C1
A polar group is usually esterified to Pi (usually serine, choline, ethanolamine, glycerol, or inositol
X = H (phosphatidic acid) - precursor to other phospholipids
X = CH2-CH2-N+(CH3)3 phosphatidyl choline
X = CH2-CH(COO-)NH3+ phosphatidyl serine
X = CH2-CH2-NH3+ phosphatidyl ethanolamine
Phosphoglycerides Structure=Function
Polar region – glycerol, phosphate group, X
Nonpolar region – fatty acid
Amphiphatic character
Ideal for forming bilayers
Phosphoglyceride
Phosphatidyl inositol Inositol as a polar head group Has roles in cell signaling as well as a cell
membrane component
O P
O
O
H2C
CH
H2C
OCR1
O O C
O
R2
OH
H
OH
H
H
OHH
OH
H
O
H OH
phosphatidyl- inositol
Ether glycerophospholipids Possess an ether linkage
instead of an acyl group at the C-1 position of glycerol PAF ( platelet activating factor) -
a potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptom
The ether linkage is stable in either acid or base
Plasmalogens: cis a,b-unsaturated ethers The alpha/beta unsaturated
ether can be hydrolyzed more easily
Sphingolipids derivatives of the lipid
sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group
Like phosphoglycerides, are also constituents of cell membranes
Can be reversibly phosphorylated and utilized as signaling molecule
Sphingolipid Derivatives Ceramide - amino group
of sphingosine forms an amide bond with a fatty acid carboxyl
Sphingomyelin has a phosphocholine or phosphethanolamine head group. common constituent of
plasma membranes similar in size and shape
to the glycerophospholipid phosphatidyl choline
H2CHC
OH
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
ceramide
Sphingolipid Derivatives Cerebroside a sphingolipid
(ceramide) with a monosaccharide such as glucose or galactose as polar head group.
Ganglioside – a ceramide with polar head group that is a complex oligosaccharide, including the acidic sugar derivative sialic acid
Both are collectively known as glycosphingolipids and are commonly found on the outer leaflet of the cell membrane
cerebroside with -galactose head group
H2CHC CH
NH CH
C
CH2
CH3
OH
C
R
O
OH O
H H
H
OHH
OH
CH2OH
HO
H
( )12
Ganglioside Structure
Ganglioside Cerebrosides
One sugar molecule Galactocerebroside – in neuronal membranes Glucocerebrosides – elsewhere in the body
Sulfatides or sulfogalactocerebrosides A sulfuric acid ester of galactocerebroside
Globosides: ceramide oligosaccharides Lactosylceramide
2 sugars ( eg. lactose) Gangliosides
Have a more complex oligosaccharide attached Biological functions: cell-cell recognition; receptors for
hormones
Cardiolipids A polyglycerol phospholipid; makes up 15% of
total lipid-phosphorus content of the myocardium – associated with the cell membrane
Cardiolipids are antigenic and as such are used in serologic test for syphilis (Wasserman test)
C
H2C O
O
H2C O P
O
OH
O
C
O
R1
C
O
R2
CH2 C
OH
H
CH2 O P O
OH
O
CH2
C OH
CH2O
C
O
R3
C
O
R4
H
glycerolglycerol
glycerol
Sulfolipids also called sulfatides or cerebroside sulfates contained in brain lipids sulfate esters of cerebrosides present in low levels in liver, lung, kidney, spleen, skeletal
muscle and heart function is not established
Lipid Storage Diseases
Lipid Storage Diease a group of inherited metabolic disorders in
which harmful amounts of fatty materials (lipids) accumulate in various tissues and cells in the body
also known as sphingolipidoses genetically acquired due to the deficiency or absence of a
catabolic enzyme Tay Sachs disease Gaucher’s disease Niemann-Pick disease Fabry’s disease
Tay Sachs Disease
Fabry’s Disease
Niemann Pick Disease
Cholesterol and related compounds
Cholesterol an important constituent of cell
membranes, has a rigid ring system and a short branched hydrocarbon tail. serves as a component of
membranes of cells (increases or moderates membrane fluidity)
precursor to steroid hormones and bile acids
storage and transport –cholesterol esters
Cholesterol is largely hydrophobic.
But it has one polar group, a hydroxyl, making it amphipathic.
C holestero lH O
cholesterol PDB 1N83
Steroid Ring System
A B
C D1
2
34
56
7
8910
1112
13
14 15
16
1718
19
Eicosanoids Includes prostaglandins and related
compounds Derivatives of arachidonic acid Serves as local hormones and
intercellular signaling Key hormones in inflammation responseCOOH
20
8
12
prostanoic acid
9
1115
Eicosanoids Types of
Eicosanoids Prostaglandins Prostacyclins Thromboxanes Leukotrienes epoxyeicosatrien
oic acids.
Biological Functions Inflammation Fever regulation of blood
pressure blood clotting immune system
modulation control of reproductive
processes and tissue growth
regulation of the sleep/wake cycle
Terpenes simple lipids, but lack
fatty acid component formed by the
combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene)
monoterpene (C-10) – made up of 2 isoprene units
sesquiterpene (C-15) – made up of 3 isoprene units
diterpene (C-20) – made up of 4 isoprene units
limonene
CHO
citronellal
OH
menthol camphene
HOH
squalene lanosterol
Terpenes tetraterpenes (C-40) are not
as common as mono, di, and triterpenes include the carotenoids such as
beta-carotene (precursor of vitamin A) and lycopene found in tomatoes
usually colorful compounds due to highly conjugated system
polyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22) examples include dolichol
phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q
Lipid-linked proteins and Lipoproteins
Lipid-linked proteins Proteins that have lipids covalently bonded to them Usually found in cell membranes 3 types are most common:
Prenylated proteins Farnesylated proteins (C15 isoprene unit) Geranylgeranylated proteins (C20 isoprene unit)
Fatty acylated proteins Myristoylated proteins (C14) Palmitoylated proteins (C16)
glycosylphosphatidylinositol-linked proteins (GPI-linked proteins) occur in all eukaryotes, but are particularly abundant in parasitic
protozoa located only on the exterior surface of the plasma membrane
Fatty acylated proteins
Prenylated proteins
GPI-linked proteins
Lipoproteins particles found in plasma that transport
lipids including cholesterol lipoprotein classes
chylomicrons: take lipids from small intestine through lymph cells
very low density lipoproteins (VLDL) intermediate density lipoproteins (IDL) low density lipoproteins (LDL) high density lipoproteins (HDL)
LipoproteinLipoprotein class
Density (g/mL)
Diameter (nm)
Protein % of dry wt
Phospholipid %
Triacylglycerol % of dry wt
HDL 1.063-1.21 5 – 15 33 29 8
LDL 1.019 – 1.063
18 – 28 25 21 4
IDL 1.006-1.019
25 - 50 18 22 31
VLDL 0.95 – 1.006
30 - 80 10 18 50
chylomicrons
< 0.95 100 - 500 1 - 2 7 84