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LIPIDS
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Primarily C and H atoms (hydrophobic)
Energy storage (~80% total), membranes, signaling molecules
Four families: fats, phospholipids, steroids, and waxes
1. Fats
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Compact energy storage
Thermal insulation for animals
Cushions organs
Triacylglycerols (triglycerides)
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Three fatty acids attached to a glycerol molecule (not a polymer)
fatty acid
fatty acid
fatty acid
Glycerol
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Triacylglycerol (TAG)
Fatty acids are usually 16 or 18 carbon atoms long
nonpolar → hydophobic
Triacylglycerol Formation
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Condensation reaction between a hydroxyl group of glycerol and the carboxyl
group of a fatty acids **Dehydration synthesis**
o Forms an ester linkage (esterification)
Ester linkage
Saturated fats
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hydrocarbon chains saturated with H atoms (no double bonds)
Straight chains fit closely together → London forces along their length →
SOLIDS at room temperature
 Predominantly produced by animals
Unsaturated fats
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1+ carbon-carbon double bonds
o Polyunsaturated fatty acids = many double bonds
 Double bond causes a bend in the fatty acid, reducing the strength of the
London forces → LIQUIDS at room temperature (oils)
 Predominantly produced by plants (olive oil, canola oil, etc.)
****Hydrogenation
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Industrial process where H-atoms are added to double bonds in unsaturated
fatty acids → semi-solids (margarine and shortening)
 Produces trans fats (almost all natural fat = cis fats)
cis
trans
2. Phospholipids
 Glycerol molecule attached to 2 fatty acid chains and a phosphate
 Amphipathic: Hydrophilic heads (phosphate group) and
hydrophobic tails (fatty acids)
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When in water phospholipids form spheres called micelles or
produce phospholipid bilayers ( liposomes)
o Hydrophilic head faces the aqueous environment and the
hydrophobic tails are tucked away from contact with water
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Polar molecules can not pass through the membrane because of the nonpolar
centre
 Cell membranes contain proteins and hydrophilic pores that allow polar
material to pass
3. Sterols: Steroids
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Compact hydrophobic molecules containing 4 fused hydrocarbon rings and
several functional groups
 Different steroids have different functional groups attached
 Lacks a fatty acid component
Cholesterol
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Precursor of all steroid hormones (e.g. sex hormones) and other compounds
such as vitamin D and bile salts
 Also present in cell membranes, where it increases membrane rigidity
Cholesterol
Estrogen
Testosterone
4. Waxes
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Long-chain fatty acids linked to alcohols or carbon rings
Hydrophobic with firm, pliable consistency
Used as waterproof coatings by plants (leaves, stems, etc.) and animals (bird
feathers, beeswax, etc.)
Omega fats
Essential fatty acids that cannot be made by the body
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alpha-linolenic acid (ALA), an essential n−3 fatty acid
eicosapentaenoic acid (EPA).
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Linoleic acid (LA)
Lipoproteins
Protein-lipid complexes that carries fat in the blood
HDL
- High Density Lipoprotein (good cholesterol)
- High protein/fat ratio
- scavengers – collect fat from body and return to liver
LDL
- Low Density Lipoprotein (bad cholesterol)
- High fat/protein ratio
- Transports fat from liver → body