Lipids (PowerPoint)

What are the kinds of lipids?
What are lipids?
Lipids are hydrophobic molecules composed of carbon,
hydrogen and oxygen. They contain fewer polar O-H
bonds and more nonpolar C-H bonds than do
carbohydrates, thus they are insoluble in water but
soluble in nonpolar substances.
Why are lipids important?
Organisms use lipids for:
1. Storing energy
2. Building membranes and other cell parts
Energy Units
One calorie = 1 cal = 4.18 J
One Kilocalorie = 1 Kcal = 1 Cal =4.18 KJ
1g of fat = 9 Kcal
1g of protein = 4 Kcal
1g of carbohydrates = 4 Kcal
* The calorie is not an SI unit
What are the most common fats found in
plants and animals?
Are the triacylglycerols (triglycerides), which
contain three fatty acids attached to a
single molecule of glycerol.
The structure of glycerol and triglycerides:
H – C – OH
H – C – OH
H – C – OH
H – C – O – fatty acid
H – C – O – fatty acid
H – C – O – fatty acid
How do fatty acids attach to glycerol?
Fatty acids attach to glycerol through a
condensation reaction that takes place
between the hydroxyl group of glycerol and
the carboxyl group of fatty acids, the
resulting bond is called an ester linkage, and
the process is called esterification.
Dehydration synthesis
Saturated and unsaturated fatty acids
Saturated fatty acids: have only single bonds
between the carbon atoms.
e.g.: stearic acid
Unsaturated fatty acids: have one or more
carbon – carbon double bonds.
e.g.: oleic acid
Stearic acid
stearic acid
Oleic acid
oleic acid
What is a wireframe or Kekule structure?
A kekule structure or a wireframe is a short notation,
where neither the carbon atoms nor the hydrogen
atoms are shown in the diagram , the carbon atoms
are assumed to exist at every free end or bend of
the wireframe.
1) Triglycerides
A saturated triglyceride
Why are the unsaturated fatty acids liquids at
room temperature?
In the triglyceride molecule, the molecule bends at
the carbon – carbon double bond of the fatty acid,
these bends and kinks keep the fatty acid tails
away from each other, reducing the number of Van
Der Waals attractions that can form along their
length, and hence are liquid at room temperature.
What does hydrogenation of oils mean?
Hydrogenation of oils is adding hydrogen
atoms to the double bonds of unsaturated
triglycerids to change them into semisolid
materials such as margarine and shortening.
2) Phospholipids
Phospholipids are composed of a glycerol molecule to
which is attached two fatty acids and a highly polar
phosphate group.
The phosphate group may be thought of as a polar
head and the fatty acids as long nonpolar tails.
The polar head is hydrophilic and the nonpolar tails
are hydrophobic.
Phospholipids and the cell membrane
The cell membranes are mostly composed of phospholipids.
3) Steroids
Steroids and the cell membrane
Membranes also contain a class of lipids called sterols
(steroids). These are compact hydrophobic
molecules containing four fused hydrocarbon rings
and several different functional groups.
Cholesterol is an important steroid component of cell
Phospholipids/Steroids and the cell membrane
Bile salts
(Digestion of fats in small intestine)
Sex hormones
Vitamin D
(Healthy Bones & teeth)
4) Waxes
Are lipids containing long chain fatty acids linked to alcohols
or carbon rings.
They are hydrophobic molecules with firm pliable consistency,
this property makes waxes ideally suited to form
waterproof coating on various plant parts to conserve water
and to prevent infection, they also cover some animal
feathers and fur ( Penguin and Polar Bear).
E.g.: the water resistant coat on cherries called cutin.

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