Lipids
Lipids
Lipids are a large and
diverse group of
naturally occurring
organic compounds that
share some general
properties.
General Properties of Lipids
1. Insoluble in water.
2. Soluble in non-polar organic solvents e.g.
ether, acetone,..
3. Contain carbon, hydrogen, and oxygen;
sometimes contain nitrogen and phosphorus.
4. On hydrolysis they give fatty acids.
5. Take part in plant and animal metabolism.
Functions of Lipids
1.
2.
3.
4.
5.
6.
Energy storage, mobilization, and utilization.
Cell differentiation and growth.
Cell membrane structure.
Signal transmission.
Hormone synthesis.
Bile acid synthesis.
Fatty Acids
Fatty acids are the building blocks of lipids;
they are straight-chain organic acids.
All fatty acids have an even number of carbon
atoms.
Fatty acids are important sources of fuel because, metabolized,
they yield large quantities of ATP. Many cell types can use
either glucose or fatty acids for this purpose. In particular,
heart and skeletal muscle prefer fatty acids
Structure of Fatty Acids
• Fatty acids consist of one carboxyl group
(-COOH) attached to a non-polar hydrocarbon
tail.
• General Formula: CH3(CH2)n -COOSaturated Fatty Acids
Non-Saturated Fatty Acids
Types of Fatty Acids
I- Saturated fatty acids:
• Contain only single bonds between carbon atoms.
• Have high melting points.
• At room temperature they are fats (solid form).
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II- Unsaturated fatty acids:
Contain one or more double bonds between carbon atoms.
Have low melting points.
At room temperature they are oils (liquid form).
They are subdivided into: Monounsaturated (one double
bond) and Polyunsaturated (many double bonds) fatty acids.
Saturated and Non-Saturated Fatty Acids
Essential Fatty Acids
• Fatty acids which are essential for the
complete nutrition of the human body.
• There are twenty different needed fatty acids
in your body, but they are all made from two:
- Linoleic acid (omega-6 fatty acid) found in
seed oils like corn, peanut, cotton seeds,..
- Linolenic acid (omega-3 fatty acid) found in
seed oils like soybeans, walnuts,..
• These two fatty acids are essential. You must get
them from the foods you eat because your body
cannot manufacture them. Thus, essential fatty acids
are the building blocks for all the other fats in your
body.
• Linoleic acid and Linolenic acid essential fatty acids
are especially important for making prostaglandins
(hormone) in your body.
• They also play a role in controlling your blood
pressure, your heart, your kidneys, your digestive
system, and body temperature.
• They are important for allergic reactions, blood
clotting and making other hormones.
Classification of Lipids
Lipids are divided into three main types:
1. Simple.
2. Complex.
3. Precursor & derived lipids.
I- Simple Lipids
• Simple lipids are esters of fatty acids.
• When hydrolyzed they yield fatty acids and
alcohol.
• If the simple lipid yield 3 fatty acids and glycerol
it is called: fat or oil.
• If the simple lipid yield one fatty acid and high
molecular weight alcohol it is called: wax.
II- Complex Lipids
When hydrolyzed they give (yield) one or
more fatty acids, an alcohol, and other
compounds.
Examples of Complex Lipids:
Phospholipids, Glycolipids, and lipoproteins.
III- Precursor and Derived Lipids
Precursor lipids
Precursor lipids are compounds produced when
simple and complex lipids are hydrolyzed to
produce fatty acids, glycerol, and other alcohols.
Derived lipids
Derived lipids are formed by metabolic
transformation of fatty acids to steroids, ketone
bodies, lipid-soluble vitamins,..
e.g: Prostaglandins, Steroids,..
Simple Lipids: FATS AND OILS
Triglycerides
Triglycerides (TAG, Triacylglycerol) are major
form of fat stored by the body. A triglyceride
consists of three molecules of fatty acid
combined with a glycerol. Triglycerides come
from the food we eat as well as from being
produced by the body
Triglycerides
Glycerol
3 Fatty Acids
FAT (TAG)
TAG
TAG
Triglycerides
• TAG that contains one type of fatty acid is
called simple TAG, whereas TAG that contains
2 or 3 types of fatty acids is called mixed TAG.
Fatty acids forming TAG can be saturated,
unsaturated, or a combination.
Uses of Fats in the Body
1. Energy source: fats produce more than
double the energy produced by proteins and
carbohydrates.
2. Storage: a mean to store food in the body for
energy and to protect internal organs.
3. Keeps our bodies warm in cold weather.
4. Present in cell structure and nerve tissues.
Physical Properties of Fats and Oils
1. Pure fats are generally white solids and oils
are generally yellow liquids.
2. Tasteless and odorless.
3. Fats and oils are insoluble in water but are
soluble in organic liquids like benzene,
acetone,..
4. Do not pass through membranes.
5. Are lighter than water.
oil
Fat
oils are insoluble in water
oils are lighter than water
Chemical Reactions of Fats
1.
2.
3.
4.
5.
React with Iodine.
Hydrolysis.
Saponification.
Hydrogenation.
Rancity.
I- Reaction with Iodine
Unsaturated fats and oils will react with
Iodine but saturated fats and oils will
not.
II- Hydrolysis
Fats will hydrolyze (break down) to form
glycerol and free fatty acids when they are
treated with enzymes, acids, or bases.
3
III- Saponification
Saponification is the heating of a fat with a
strong base (e.g. NaOH or KOH) to produce
glycerol and the salt of fatty acid. The Na or K
salts of a fatty acid are called Soaps.
FAT + NaOH or KOH
Heat
Soap
Saops
Saponification
VI- Hydrogenation
Hydrogenation is the process of converting
vegetable oils to fats by the addition of
hydrogen in the presence of a catalyst.
In this process some but usually not all of the
double bonds in oils have been reduced by the
addition of H2 e.g. Margarine.
Hydrogenation
Margarine
V- Rancidity
When fats are left at room temperature for a
short period of time they develop unpleasant
odor and taste i.e. they become Rancid. This
occurs due to 2 reactions: oxidation and
hydrolysis of fat.
Complex Lipids: PHOSPHOLIPIDS
Structure of Phospholipids
Phospholipids are complex fat in which one
fatty acid has been replaced by phosphoric
acid (phosphate group) and one of several
nitrogen-containing molecules. Phospholipids
are found in all tissues in the human body,
especially brain, liver, and spinal tissue and
also in cell membranes.
When hydrolyzed they give (yield) one or
more fatty acids, an alcohol, and other
compounds
Types of Phospholipids
According to the alcohol part, phosphospholipids
are divided into:
1. Phosphoglycerides: contain glycerol. E.g.
Lecithin, cephalins.
2. Phosphosphingosides: contain sphingosine. E.g.
sphingomyelins.
Properties of Phospholipids
Amphipathic:
Amphipathic lipids are molecules that have
non-polar (hydrophobic) end or tail and a
polar or ionic (hydrophilic) end or head.
Complex Lipids: GLYCOLIPIDS
They are sugar containing lipids also called
cerebrosides because they are found in large
amounts in the brain tissue.
Structure of Glycolipids
Glycolipids are composed of one fatty acid, one
sphingosine molecule, and a galactose sugar.
There are many types depending on the type of
fatty acid present.
Complex Lipids: LIPOPROTEINS
Lipoproteins are lipids associated with special proteins
to give plasma lipoproteins.
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Examples of Lipoproteins
Chylomicrons: 90% lipids and 10% protein.
Very Low Density Lipoproteins (VLDL): 60% lipids and
40% protein.
Low Density Lipoproteins (LDL): 8% lipids and 92%
protein.
High Density Lipoproteins (HDL): 5% lipids and 95%
protein.
The Cell Membrane
Cell membranes are composed of 40-50%
lipids, 50-60% proteins, cholesterol, and a
small amount of carbohydrate. These
components vary in amounts depending on
the type of cells.
Functions of the Cell Membrane
1. Give structure and protection to the cells.
2. Hold up proteins that transport molecules
across the cells.