13.1-13.2
LIPIDS
13.1: WHAT ARE LIPIDS?

Lipids have three important roles in human
biochemistry
 Energy
is stored within fat cells
 Help
to separate aqueous solutions in cell
membranes
 They
serve as chemical messengers
STORAGE

Animals and humans store energy in fat cells

When fats are burned, they produce twice as
much energy as carbohydrates produced
MEMBRANE COMPONENTS

Lipids are not water soluble due to the polar
groups being much smaller then the nonpolar
parts

This makes them perfect for separating
compartments within cells
MESSENGERS

Serve as chemical messengers

Steroid hormones are primary messengers

Prostaglandins and thromboxanes are
examples of secondary messengers who
activate the hormones responses
CLASSIFICATION OF STRUCTURE

Four lipid groups
 Simple
lipids(fats and waxes)
 Complex
lipids
 Steroids
 Prostaglandins,
thromboxanes, and leukotrienes
13.2 STRUCTURE OF TRIGLYCERIDS
Triesters of glycerol of long-chain carboxylic
acids
 Alcohol of triglycerides are always glycerol
 Acid component may be any number of fatty
acids
 Animal fats and plant oils

TRIGLYCERIDES & FATTY ACIDS
Unbranched carboxylic acids
 Chains from 10-20 carbons
 Even number carbon chains
 One functional group (OH – hydroxyl)
 Cis-isomer predominates

TRIACYLGLYCEROLS
Triglycerides
 Most common lipid material
 Mono & triglycerides are not infrequent

HYDROPHOBIC
Caused by long hydrocarbon
 Ester groups are buried in non-polar
environment
 Insoluble in water

13.3 PROPERTIES
Fats are usually solid at room temp
 Liquids are oils (plant and fish)

PHYSICAL PROPERTIES

Solid animal fats contain saturated fatty acids
 Some

Vegetable oils contain high amounts of
unsaturated fatty acids
 Some

have unsaturated
have saturated
Colorless, odorless, tasteless,
 Flavor
is caused by other dissolved substances
COCONUT AND VEGETABLE OIL

Vegetable Oil
 High

amounts of unsaturated fatty acids
Coconut Oil
 Small
amount of unsaturated fatty acids
 Rich in low-molecular-weight fatty acids
 (chiefly lauric acid)
ESSENTIAL FATTY ACIDS
Unsaturated fatty acids
 Linoleic and linolenic aicds
 Body cannot synthesize these acids
 Obtained from our diet

POLYUNSATURATED

Oils with an average of more than one double
bound per fatty acid chain
HYDROGENATION

Reduce C-C double bonds to single bonds
 Treated
with hydrogen and a catalyst
Hydrogenate all double bonds, a fat with no
double bonds may be too solid
 Margarine – partial hydrogenation of veg oils

 Contains
more unsaturation than fully
hydrogenated shortenings

Source of trans fatty acids
SAPONIFICATION

Glycerides are subjected to hydrolysis
 Carried

out by acids or bases
Base-promoted hydrolysis of fats and oils
producing glycerol and a mixture of fatty acid
salts
 Soaps