Download OILS

Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 18:
Lipids
Jennifer P. Harris
IMPORTANT FUNCTIONS OF LIPIDS
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Protective wax coatings found on some plants
Energy-rich compounds with low densities
Storage form of energy for plants and animals
Structural components, especially in cellular membrane
formation
LIPID CLASSIFICATION
• Lipids are biological compounds that are soluble only in
nonpolar solvents.
LIPID CLASSIFICATION (continued)
• Saponifiable lipids contain an ester that can undergo basic
hydrolysis.
• Triglycerides, waxes, phospholipids, and sphingolipids
• Simple lipids contain a fatty acid and alcohol.
• Triglycerides and waxes
• Complex lipids contain a fatty acid, alcohol, and other
components.
• Phospholipids and sphingolipids
• Nonsponifiable lipids do not contain an ester and cannot be
hydrolyzed.
• Steroids and prostaglandins
FATTY ACIDS
• Fatty acids:
• are the building blocks of many lipids.
• are long chain carboxylic acids.
• have long nonpolar tails responsible for fatty/oily
characteristics.
• The carboxyl group is very hydrophilic under conditions of
physiological pH (exists as –COO-).
FATTY ACIDS (continued)
• In water, fatty acids will form spherical clusters called
micelles.
• Micelles are important for biological functions, like the
transport of insoluble lipids in the blood.
FATTY ACIDS (continued)
• Fatty acids are:
• usually straight chains (no branching).
• usually from C10 to C20.
• usually an even number of carbons.
• either saturated (no C=C bonds) or unsaturated (has C=C
bonds, usually in the cis configuration).
• Examples of saturated, monounsaturated, and
polyunsaturated fatty acids containing 18 carbon atoms
include:
FATTY ACIDS (continued)
• Cis C=C causes “kinking” of the carbon chain:
FATTY ACIDS (continued)
• Fatty acids with C=C bonds
cannot pack closely together
because of shape. This leads to
decreased intermolecular
attractions and lower melting
points.
• Fatty acid melting points
decrease as the number of C=C
bonds increases.
• Most unsaturated fatty acids are
liquids at room temperature.
FATTY ACIDS (continued)
• Essential fatty acids are those needed by the body, but not
synthesized within the body in adequate amounts.
• For humans, linoleic and linolenic acid are essential, but easily
obtainable from plant and fish oils.
FATTY ACIDS (continued)
• Linoleic (an omega-3 fatty acid) and linolenic (an omega-6
fatty acid) acids:
• are used to produce hormonelike substances that regulate
a wide range of functions and characteristics, including:
• e.g. blood pressure, blood clotting, blood lipid levels,
the immune response, and the inflammation response
to injury and infection.
• can be converted to other omega-3 and omega-6 fatty
acids.
STRUCTURE OF FATS AND OILS
• Fats are:
• usually from animal sources.
• solids at room temperature.
• usually composed to a high degree of saturated fatty
acids.
• Oils are:
• usually from plant and fish sources.
• liquids at room temperature.
• usually composed of more unsaturated fatty acids than
fats.
STRUCTURE OF FATS AND OILS (continued)
• Fats and oils are triglycerides (triacylglycerols) which are
triesters of glycerol.
STRUCTURE OF FATS AND OILS (continued)
• Fatty acid components in naturally occurring triglyceride
molecules are rarely identical.
• Natural triglycerides are usually mixtures of different
triglyceride molecules.
STRUCTURE OF FATS AND OILS (continued)
• An example of the esterification process:
STRUCTURE OF FATS AND OILS (continued)
• Excessive fat in the diet:
• is recognized as a risk factor influencing the development
of chronic disease.
• is a concern because of its role in raising blood
cholesterol levels.
• High cholesterol is a risk factor in the development of
coronary heart disease (leading cause of death in
Americans every year).
REACTIONS OF FATS AND OILS
• Hydrolysis is important for fat and oil digestion.
• Enzymes (lipases) can catalyze the hydrolysis process.
REACTIONS OF FATS AND OILS (continued)
• Saponification is the commercial production of the salts of fatty
acids (soaps).
REACTIONS OF FATS AND OILS (continued)
• Soaps depend on the base used for saponification.
• Sodium salts (hard salts) found in cake soap.
• Potassium salts (soft soaps) found in shaving creams and
liquid soap preparations.
• Traditional soap making:
• uses animal fat is the source of triglycerides.
• uses lye (crude NaOH) or an aqueous extract of wood
ashes is the source of the base.
• was lost with fall of Roman Empire.
• The soapless centuries AD 500-1500 resulted in
devastating plagues in an unsanitary western Europe.
REACTIONS OF FATS AND OILS (continued)
• Hydrogenation decreases the degree of unsaturation and is
used to make margarines from oils.
• Complete hydrogenation results in a hard and waxy product.
• Partial hydrogenation results in a smooth, creamy product
that is desired by consumers.
• Isomerization of cis to trans fatty acids will occur during this
process.
• Current dietary advice includes reducing the consumption of
saturated and trans fatty acids.
TRIGLYCERIDE REACTION MAP
WAXES
• Waxes are esters of fatty acids and long chain alcohols (1232 carbon atoms). They are:
• water insoluble and not easily hydrolyzed.
• often found in protective coatings.
• used commercially to make cosmetics, candles,
ointments, and protective polishes.
WAXES (continued)
PHOSPHOGLYCERIDES
• A phosphoglyceride is a phospholipid that contains glycerol,
fatty acids, phosphoric acid, and an alcohol (usually an amino
alcohol).
PHOSPHOGLYCERIDES (continued)
PHOSPHOGLYCERIDES (continued)
• Lecithins:
• contain the amino alcohol choline.
• are an important cell membrane component.
• are emulsifying and micelle-forming agents.
• Cephalins:
• contain ethanolamine or serine as the alcohol.
• are found in most cell membranes, especially brain tissue
and blood platelets (role in blood-clotting process).
PHOSPHOGLYCERIDES (continued)
• Phosphatidylcholine (lecithin):
PHOSPHOGLYCERIDES (continued)
• Cephalin: