Lesson 7: Lipids Flashcards
Lipids
Lipids contain carbon, hydrogen and oxygen.
Lipids are insoluble in water but they are soluble in polar
solvents.
The most common lipids are fats, oils, steroids and
phospholipids.
Fats and Oils
The major component of fats and oils are triglycerides.
Triglycerides are composed of one glycerol and three fatty acids.
Glycerol is a molecule of three carbons, each of which contains an
alcohol group.
Fatty acids are long chain carboxylic acids.
An esterification reaction takes place
between the carboxyl group of a fatty acid
and each of the hydroxide groups of the
glycerol.
This forms an ester link
A glycerol condenses with three fatty acids
to form a triglyceride.
The three fatty acids that form a
triglyceride do not have to be the same.
Fatty Acids
Fatty acids differ in the length of the
carbon chain (14-22) and the position
and number of double bonds between
carbons.
Fatty acids with no double bonds are
called saturated
Fatty acids with one double bond are
called monounsaturated
Fatty acids with more than one
double bond are called
polyunsaturated
Saturated Fatty Acids
Saturated fatty acids have high melting points, are solid at room
temperature.
These are known as fats and are derived from animals.
These properties are the result of the carbon –carbon single bond angles
being tetrahedral (109.5) which allows them to pack closely together which
leads to significant van der Waals forces between molecules.
Unsaturated Fatty Acids
Unsaturated fatty acids have lower melting points and are liquid at room
temperature.
These are known as oils and are derived from plants.
The properties are caused by the carbon-carbon double bond having a bond
angle of 120 which creates kinks in the chain that make packing close
together difficult which leads to lower intermolecular forces.
Essential Fatty Acids
The human body can synthesize all of the fatty acids it requires except two:
Linoleic acid (omega-6-fatty acid)
Linolenic acid (omega-3-fatty acid)
The terms omega-6 and omega-3 indicate the position of the first double bond in
the molecule relative to the terminal -CH3 group to represent its distance from the
carboxyl group.
These fatty acids must be obtained in the diet.
They are found in plants and fish.
These essential fatty acids play a role in prostaglandin production and help lower
LDL cholesterol.
Digestion of Fats and Oils
Since fats and oils are insoluble they must be broken down into fatty acids
and glycerol in order to be transported.
This is done through the process of hydrolysis which is controlled by a
group of enzymes known as lipases.
These are the slowest molecules to break down in the digestive system as
lipases act sequentially in different parts of the digestive system.
Steroids
Lipids with a four fused ring
structure.
The most important is
cholesterol which is used by the
body to synthesize hormones.
Cholesterol is present in out diet
and made by the body.
Cholesterol
Cholesterol has been linked with many circulatory conditions.
Cholesterol is insoluble in blood, therefore it is transported by binding to
different phospholipids.
LDL (low density lipoprotein)
HDL (high density lipoprotein)
Phospholipids
Similar to triglycerides but they only have two fatty acids condensed onto
the glycerol.
The remaining hydroxide group condenses with a phosphate group.
Phospholipids vary in the fatty acids attached and the group that binds with
the phosphate.
The most common phospholipid is lecithin.
Structure of
Lecithin
Phospholipids have a hydrophilic
head region and a hydrophobic tail
region.
This causes them to spontaneously
form phospholipid bilayers that
maximize the interaction of the
polar region with water while the
interior is non polar.
The bilayer is the basis of
membrane structure
Function of Lipids
Lipids contain stored energy.
Since lipids are less oxidized than carbohydrates, they can undergo more oxidation and therefore
release more energy per unit mass.
A gram of lipid releases twice as much energy as a gram of carbohydrate.
However, the energy in lipids is not as readily available since more reactions are required to break it
down.
Cholesterol is a component of cell membranes (keeps membrane fluid) and also serves as the basis of
steroid hormones.
Bile salts (aid in the digestion of fats) are also steroid based.
Phospholipids are components of cell membranes which govern transport into and out of the cell
Lipids help absorb fat-soluble vitamins such as A,D,E, and K.
Adipose Tissue
The fat storing cells in the body are known as adipose tissue.
Adipose tissue surrounds the organs, such as the kidneys, for
protection and a layer of adipose tissue insulates the body.
Lipids in our Diet
The food industry uses addition reactions to chemically modify the fats
that we eat.
This decreases the degree of unsaturation across the fat.
This creates a fat with a higher melting point which allows it to be solid
at room temperature for easy transport and storage.
This also gives the fat a longer shelf life.
Hydrogenation requires the fat to be
exposed to heat and pressure which
affects the remaining double bonds by
altering the position of the groups.
The groups are altered from a cis position
to a trans position.
These are known as trans fats.
Trans fats are present in many processed
foods and are always present if the food
is labelled “partially hydrogenated”
Consuming trans fats raises the level of
LDL cholesterol which is a risk factor for
heart disease and reduces HDL
cholesterol which protects against heart
disease.
Effects of Excess Lipids
Atherosclerosis is caused by lipid deposits on the walls of major blood
vessels.
The low solubility of lipids allows this deposit to occur. The deposits
lead to high blood pressure and heart disease.
Obesity is caused by the storage of excess lipids in adipose tissue.
Linked to many health issues such as diabetes, cancer and heart
disease.
