FACT
You will learn more
about how
cholesterol can clog
arteries and lead to
heart disease in the
chapter on
transport systems in
animalsFigure 2.14: Fatty acids can be saturated, mono-unsaturated or polyunsaturated depending on the
number of double bonds present. Double bonds result in ”kinks” in the fatty acid chain.
Cholesterol
Cholesterol is an organic chemical substance known as asterol. You are not required to
understand its molecular makeup or its structural composition. It is an important component
in cell membranes. The major dietary sources of cholesterol include cheese, egg, pork,
poultry, fish and shrimp. Cholesterol is carried through the body by proteins in the blood
known aslipoproteins. A lipoprotein is any combination of lipid and protein.
Cholesterol is carried in the blood through the body byhigh density lipoprotein,low density
lipoproteinand throughtriglycerides.
1.Low density lipoprotein (LDL): Low density lipoprotein transports cholesterol around
the body. It has a higher proportion of cholesterol relative to protein. It is often known
as ”bad” cholesterol because higher levels of LDL are associated with heart disease.
2.High density lipoprotein (HDL): High density lipoprotein is the smallest of the lipopro-
teins. It has a high proportion of protein relative to cholesterol and is therefore often
known as the ”good” cholesterol. HDL transports cholesterol away from cells and to
the liver where it is broken down or removed from the body as waste.High levels of LDL can cause heart disease. Cholesterol builds up in blood vessels that carry
blood from the heart to the tissues and organs of the body, called arteries. This leads to a
hardening and narrowing of these vessels, which interferes with the transport of blood, and
can potentially lead to a heart attack. The biggest contributor to the amount of cholesterol in
your blood is the type of fats you eat. Saturated fats are less healthy than unsaturated fats as
they increase the amount of LDL cholesterol in your blood.
Test for lipids
The test for lipids relies on the fact that lipids leave a translucent ‘grease spot’ on brown
paper bags, while non-lipid substances do not.
Chapter 2. The chemistry of life 37