Lipids – Structure, types and Functions (Biological Molecules) Part 1 |Biochemistry lecture|

Lipids are a diverse group of hydrophobic molecules. Lipids are varied in form and function.
They include waxes and certain pigments, but we will focus
on the types of lipids that are most biologically important:
fats, phospholipids, and steroids.
A fat is constructed from two kinds of smaller molecules:
glycerol and fatty acids . Glycerol is an alcohol;
each of its three carbons bears a hydroxyl group. A fatty
acid has a long carbon skeleton, usually 16 or 18 carbon
atoms in length.
In making a fat, three fatty acid molecules are each joined
to glycerol by an ester linkage, a bond formed by a dehydration
reaction between a hydroxyl group and a carboxyl
group. The resulting fat, also called a triacylglycerol, thus
consists of three fatty acids linked to one glycerol molecule.
The terms saturated fats and unsaturated fats are commonly
used in the context of nutrition. These
terms refer to the structure of the hydrocarbon chains of
the fatty acids. If there are no double bonds between carbon
atoms composing a chain, then as many hydrogen atoms as
possible are bonded to the carbon skeleton. Such a structure
is said to be saturated with hydrogen, and the resulting fatty
acid is therefore called a saturated fatty acid .
An unsaturated fatty acid has one or more double bonds,
with one fewer hydrogen atom on each double-bonded carbon.
Nearly all double bonds in naturally occurring fatty acids
are cis double bonds, which cause a kink in the hydrocarbon
chain wherever they occur.
Phospholipids
Cells as we know them could not exist without another
type of lipid—phospholipids. Phospholipids are essential
for cells because they are major constituents of cell membranes.
a phospholipid is similar to a fat molecule but
has only two fatty acids attached to glycerol rather than
three. The third hydroxyl group of glycerol is joined to a
phosphate group, which has a negative electrical charge
in the cell.