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 is 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, glycerolipids, spingolipids, and polyketides.
Now, fatty acids are a 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 then that's nonpolar
and cannot act -- 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 the fat is, the more double bonds it contains.
Fats also vary in -- or 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 two carbons each.
The smallest being lauric acid with 12 carbons, myristic with 14,
palmitic acid with 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 a 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 caboxyl group, that can ionize at physiological pH.
The rest of the molecule contains only carbon and hydrogen, and is very nonpolar.
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 single 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 our membranes.
Now, this shows a structure of oleic acid, and you can notice the double bond in oleic acid.
The biological fatty acids almost always contain a 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 risk 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 is contained by normal biological -- biologically-produced fatty acids
has a physical bend located inside of it.