Another major class of lipids is steroids, which have structures
totally different from the other classes of lipids. The main
feature of steroids is the ring system of three cyclohexanes
and one cyclopentane in a fused ring system as shown below. There
are a variety of functional groups that may be attached. The
main feature, as in all lipids, is the large number of carbon-hydrogens
which make steroids non-polar.
Steroids include such well known compounds as cholesterol,
sex hormones, birth control pills, cortisone, and anabolic steroids.
Cholesterol - Chime
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The best known and most abundant steroid in the body is cholesterol.
Cholesterol is formed in brain tissue, nerve tissue, and the
blood stream. It is the major compound found in gallstones and
bile salts. Cholesterol
also contributes to the formation of deposits on the inner walls
of blood vessels. These deposits harden and obstruct the flow
of blood. This condition, known as atherosclerosis, results in
various heart diseases, strokes, and high blood pressure.
Much research is currently underway to determine if a correlation
exists between cholesterol levels in the blood and diet. Not
only does cholesterol come from the diet, but cholesterol is
synthesized in the body from carbohydrates and proteins as well
as fat. Therefore, the elimination of cholesterol rich foods
from the diet does not necessarily lower blood cholesterol levels.
Some studies have found that if certain unsaturated fats and
oils are substituted for saturated fats, the blood cholesterol
level decreases. The research is incomplete on this problem.
| Quiz: Cholesterol exists as an ester
with fatty acids.What is the functional group at carbon 3 which
is used to make an ester?
|What is the feature on carbon 17?