Lipids
 Lipids are a major source of energy used by cells, however lipids are more difficult for your body to break
down. They produce nearly twice the amount of energy than proteins or carbohydrates.
 Lipids are essential in our diets as they:
 Are useful as insulation,
 Are necessary components of cell membranes,
 help absorb vitamins,
 are even useful in hormone production.
 Lipids are used to store and excess energy from extra carbohydrates in
animals
 Lipids are made up of Carbon, Hydrogen, and lesser amounts of Oxygen
when compared to carbohydrates
 They are generally non-polar, thus they do not dissolve in water; this
insolubility in water contributes to their ability to form cell membranes.
Lipids in living organisms fall into 5 main categories:
1. Fatty Acids
2. Fats
3. Phospholipids
4. Steroids
1) Fatty Acids
Fatty acids are molecules that consist of a single hydrocarbon
chain with a carboxyl functional group (-COOH) at one end. It is
this carboxyl group allows for the fatty acid chain to interact with
other molecules and gives it its acidic properties.
Fatty acid chains consist of four or more carbons in their
hydrocarbon backbone. The most common forms of fatty acids have
an even number of carbons ranging from 14 to 22.
Saturated chains are chains that are made up of carbons bonded
together by single covalent bonds. An unsaturated chain made have
one or more double covalent bonds between carbons making up the
chain.
Monounsaturated, only one double covalent bond present in the
chain, polyunsaturated chain has many double covalent bonds
present.
5. Waxes
Saturated Fats vs. Unsaturated Fats
Saturated fats
 Contain as many hydrogen atoms as possible with single covalent bonds between the Carbon
atoms
 Common in animals.
 Difficult to digest.
 In general, the greater number of hydrogen atoms, the firmer the fat.
Unsaturated fats
 Some hydrogen atoms are missing due to the double bonds present in the molecule.
 Commonly found in plants and are in the oil variety. (canola oil, olive oil, sunflower oil, etc.)
 Mono-unsaturated fats:
 Considered to be the healthiest type of fat. Believed to lower cholesterol and may assist in
reducing heart disease.
 Ex. Olive oils, nuts, seeds. Commonly found in plants.
Monounsaturated fatty acid
 Poly-unsaturated fats:
 Found in vegetable oils like soybean, corn, sunflower and safflower. They also occur in oily
fish.
 Look for Omega-3 fatty acids as they are essential fatty acids (EFA’s).
Polyunsaturated fatty acid
Double bonds react more easily, which means the double bonds of the unsaturated fats are more easily
broken down for the cells of your body.
But what are Trans fats?
 Unsaturated fats in foods make it more likely to spoil, so scientists found a way to add hydrogen to
these fats, creating hydrogenated fats, or Trans fatty acids.
 Trans fats tend to raise total blood LDL cholesterol levels (Bad cholestrerol).
 Example: Margarine made of olive oils (BECEL)
2) Fats (Triglycerides)
 Most common type of Lipid.
 Made up of one glycerol molecule and three fatty acid chains linked together by a dehydration
synthesis between the hydroxyl group of the glycerol and the carboxyl group of the fatty acid
 Fats obtained from animals, such as butter and lard usually contain only saturated fatty acids so they
are called saturated fats.
 Fats derived from plants such as olive oil, usually contain more unsaturated and polyunsaturated
fatty acids which is why they are called unsaturated fats. These are generally referred to as oils.

The more saturated fats, such as butter, are solid because their chains are long and straight and can
be packed closely together to form a solid structure at room temperature. Fatty acids that have kinks
(ex: double bonds) are bent and cannot be packed as tightly as saturated fats. These molecule are
more fluid at room temperature.
3) Phospholipids
 Cells could not exist without the phosphate containing lipids called phospholipids as they are the primary lipid
of the cell membranes.
 One of the fatty acid chains bound to the
glycerol backbone is replaced by a charged
phosphate group.
 This forms a polar end that is water soluble.
 This molecule has one end that is water
soluble, and one end that is soluble in oils and
grease
 Phospholipids make up the lipid bilayer of the cell membrane. The hydrophilic end of a phospholipid faces
outward toward the water, and the hydrophobic fatty acid tails face inward toward each other.
4) Steroids
Steroid - is a lipid that is composed of four carbon rings.
Sterol is the most abundant steroid and has a single -OH (hydroxyl) group at one end of the ring framework and a
complex hydrocarbon chain at the other. The -OH gives this otherwise hydrophobic molecule a slight hydrophilic
character at one end.
Cholesterol is a steroid that
 is essential for animal cell membranes and
 converts into a number of compounds; such as vitamin D.
Cholesterol can also be harmful. A high concentration of cholesterol in your diet may lead to atherosclerosis and
eventually to heart attacks.
Sex hormones, such as; estrogen, progesterone, and testosterone are specialized steroids, that control the
development of secondary sex characteristics as adolescents reach puberty.
Anabolic steroids, banned by all major sporting bodies, mimics testosterone and are used by athletes to increase
muscle mass, and are used to gain an advantage over other competitors. Steroids can be very harmful to your
body.
5) Waxes
Wax - is a lipid that is formed when long fatty acid chains are joined to alcohols or carbon rings.
Waxes are hydrophobic, extremely non-polar, and ideal for water proofing in plants and animals.
Please review your notes, and with the help of the textbook, complete the following table as a summary for Lipids.
Type
Structure
Fatty Acids
Carboxyl group linked to a
hydrocarbon chain
Fat
Function
Example
Energy storage
Insulation
Phospholipid
Steroid
Wax
Wax coating on fruit,
leaves and stems