Page 89 - Demo 1

The bulk of the membrane that surrounds cells and organelles is made up of a
bilayer of phospholipids. A cell membrane is crical to the structure and funcon
of a cell; thus, phospholipids are essenal to humans and other organisms.
Steroids: Building Blocks of Hormones and Vitamins

Steroids are lipids that are composed of four fused rings. They are
similar to phospholipids and fats because of their hydrophobic nature, but are
also different because they do not contain fay acids.

Cholesterol is a steroid that makes up the cell membrane of an animal
cell. It is the precursor of sex hormones, such as testosterone and estrogen and
vitamins, such as Vitamin E and Vitamin K. Cholesterol is mainly synthesized in
the liver and is important in the producon of bile salts which help in the
breakdown of fats and their subsequent absorpon by cells.

Figure 41. Structure of Common Steroids
Source: http://1.bp.blogspot.com/--Ajmzn6H5eM/UPi8nI4p9SI/AAAAAAAAA8I/uuOG7HaAxT8/s1600/steroids.gif

Waxes: Protecve Coang
Waxes are composed of an ester of a long-chain alcohol (–OH) and a
fay acid. Examples of animal waxes include beeswax and lanolin. Some animals
also have wax-coated fur or feathers to repel water. Many plants have leaves
and fruits with wax coangs to help prevent them from drying out. Unlike most
waxes, ear wax is composed of phospholipids and esters of cholesterol.

81