Though the word 'fat' may strike terror in
the hearts of many people, it's true that
fats are important storage forms of energy,
for animals and oils, in the case of plants.
In the picture you can see on the right here,
there's an obese mouse and a normal mouse.
The obese mouse lacking a gene called leptin
that has induced its obesity. Lipids are compounds
that include the category of fats and oils
and in this talk I'm going to talk about some
of those components. These will include fatty
acids, glycerol lipids, sphingolipids and
Now fatty acids are part of what makes a fat
molecule and fatty acids are interesting lipids
in the sense that they are amphiphilic. Amphiphilic
molecules are molecules that have a portion
of them that is very polar and can interact
with water and another portion of them that's
nonpolar and cannot interact with water. Fatty
acids of course are used to make soaps.
Fatty acids vary in their saturation, saturation
referring to the amount of single bonds that
it has. The less saturated a fat is, the more
double bonds it contains. Fatty acids also
vary in their length.
Now we can see here the most common fatty
acids that are found in cells. These are the
saturated fatty acids and you can notice that
they differ in size by 2 carbons each, the
smallest being lauric acid with 12 carbons,
myristic with 14, palmitic acid was 16, stearic
with 18 and arachidic acid with 20 carbons.
The reason that they differ in carbons by
two is that the synthesis of fats occurs with
the unit that adds two carbons every time.
This is a depiction of the structure of one
of the fatty acids here, stearic acid and
you can see on the left side a carboxyl group
that can ionize at physiological pH. The rest
of the molecule contains only carbon and hydrogen
and is very nonpolar and it's for this reason
that we describe fatty acids as being amphiphilic.
Fatty acids are also unsaturated, that is,
some fatty acids don't contain all double
bonds. Palmotoleic acid for example, contains
16 carbons, but one of the bonds in that molecule
is a double bond. Oleic acid contains 18 carbons
with one double bond and you can see linoleic
has 18 with two double bonds, linolenic 18,
with three double bonds and arachidonic acid
has 20 carbons with four double bonds. Each
of these fatty acids is very important for
making fats and the components that make up
Now, this shows the structure of oleic acid and
you can notice the double bond in oleic acid.
The biological fatty acids almost always contain
the double bond in the cis configuration.
Most people have heard of trans fats and trans
fats are usually produced as a result of chemical
modification of food and have some health
risks associated with them. You can see on
the screen here a common trans fatty acid
known as elaidic acid, compared to oleic acid,
and you can notice the difference in shape
of these molecules. The cis bond that's contained
by normal biologically produced fatty acids
has a physical band located inside of it.