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Lipids
Have four main physiological roles
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3
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Fatty acids are fuel molecules
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Simple lipids: Esters of fatty acids with various alcohols
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Fats: Esters of fatty acids with glycerols
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Fatty acids

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•

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Natural fats – usually straight chain derivatives containing an even number of
carbon atoms
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Saturated – no double bonds
Unsaturated –has double bonds
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– In fully saturated there is freedom of rotation around each carbon-carbon
bond which gives the hydrocarbon chain greater flexibility: the most stable
conformation is the fully extended chain in which steric hindrances are
minimal
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Molecules can not pack as tightly as fully saturated fatty acids and
their interactions with each other is weaker
– Because it takes less thermal energy to disorder the poorly ordered arrays of
unsaturated fatty acids, they have lower melting points than saturated fatty
acids of the same chain length
– Membrane lipids which must be fluid at all environmental temperatures are
more unsaturated than storage lipids
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Waxes serve as energy stores and water repellents
• Biological waxes are esters of long-chain (C14 to C36) saturated and unsaturated fatty acids
with long-chain (C16 to C30) alcohols
• In plankton waxes are the chief storage form of metabolic energy
• Their melting points are generally higher than those of triacylglycerols
• Certain skin glands of vertebrates secrete waxes to protect hair and skin and to keep it pliable,
lubricated and water proof
• In waterfowls feathers are coated in waxes

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STRUCTURAL LIPIDS IN MEMBRANES
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Its absence from the lungs of
premature infants causes respiratory distress syndrome

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0 that
distinguishes them from globosides

• Sphingolipids at cell surfaces are sites of biological recognition
– The carbohydrate moieties of certain sphingolipids define the human
blood groups

Sphingosine
Fatty acid
Ceramide

O Antigen
Glc

Gal

GalNAc

Gal

Fuc

A Antigen
GalNAc
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B Antigen

Gal

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Does not occur in plants
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A major constituent of plasma membranes and lipoproteins
Sterols are also precursors of
• Steroid hormones
• Bile acids are polar derivatives of cholesterol that act as detergents in the
intestine
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LIPIDS AS SIGNALS, COFACTORS, AND PIGMENTS IN
MEMBRANES
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– Thromboxanes
• Produced by platelets and act in the formation of a blood clot and the reduction of
blood flow to the site of the clot
• Nonsteroidal anti-inflammatory drugs (NSAIDs) eg aspirin, ibuprofen etc
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Fat soluble vitamins (A, D, E and K)

D and A serve as hormone precursors
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Vitamin D3 (cholecalciferol)

7-dehydrocholesterol
UV light

2 steps in skin

Regulates gene expression - turning
on the synthesis of an intestinal Ca 2+ -binding
protein which in turn regulate calcium uptake in
the intestine and calcium levels in the kidney and
bone
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Vit K2 (menaquinone) is
formed by bacteria residing in the vertebrate intestine

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Why is it that at room temperature animal fats have a waxy consistency, whereas fats
from plants are oily liquids?
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Which enzymes break triacylglycerols to form glycerol and fatty acids?
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Which lipid is a very effective surface detergent, preventing adhesion, due to surface
tension, of the inner surfaces of the lungs
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Which paracrine hormone stimulates contractions of the uterine smooth muscles
during menstruation and labour?
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Which vitamin plays a role in calcium metabolism?
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Which vitamin is deficient in infants who suffer from hemorrhagic disease of the new
born?
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