Everything Life Sciences Grade 10

FACT

When drawing
organic molecules,
it can easily get
confusing writing
out all of the ’C’s
and ’H’s for carbon
and hydrogen
respectively.
Scientists overcome
this by drawing the
carbon backbone,
and leaving out the
hydrogens. Carbon
will always make 4
bonds with other
atoms, so it is easy
to figure out how
many hydrogens
there must be. The
carbon is indicated
by a point, and the
bonds between
carbon molecules
are indicated by
lines joining the
points.

FACT
You will learn about
the important role
that lipids play in
cell membranes in
the following
chapter onthe basic
units of life.

Lipids contain carbon (C), hydrogen (H) and oxygen (O) but have less oxygen than carbohy-

drates. Examples of lipids in diet include cooking oils such as sunflower and olive oil, butter,

margarine and lard. Many nuts and seeds also contain a high proportion of lipids.

Structural composition

Triglycerides are one of the most common types of lipids. Triglyceride molecules are made

up of glycerol and three fatty acids (Figure 2.14). The fatty acid tails are made up of many

carbons joined together. The number of carbons in the fatty acid chains can differ.

Figure 2.13: A triglyceride molecule.

Role in animals and plants

Lipids are an important energy reserve and contain 37.8 kilojoules (kJ) of energy per gram.

Triglyceride lipids are broken down to release glycerol and fatty acids. Glycerol can be con-

verted to glucose and used as a source of energy, however the majority of energy provided

by lipids comes from the breakdown of the fatty acid chains. Some fatty acids are essential

nutrients that cannot be produced by the body and need to be consumed in small amounts.

Non-essential fatty acids can be produced in the body from other compounds.

Lipids are important for the digestion and transport of essential vitamins, help insulate body

organs against shock and help to maintain body temperature. Lipids also play an important

role in cell membranes.

Saturated and unsaturated fats

Carbon can form four bonds with other atoms. Most carbons in a fatty acid chain are bonded

to two adjacent carbons, and to two hydrogen atoms. Fatty acids which form four single

bonds, and have the maximum number of hydrogen atoms are calledsaturatedfatty acids

because they are ”saturated” with hydrogen atoms. However, sometimes two adjacent car-

bons will from a double bond. In this case the carbons taking part in the double bond are

each joined to only one hydrogen. Fatty acids that have carbon-carbon double bonds are

known asunsaturated, because the double bond can be ’broken’ and an additional bond

with hydrogen can be made. Double bonds are stronger than single bonds and they give

the fatty acid chain a ’kink’. These kinks mean that the molecules can not pack together

tightly, and the lipids are more fluid. This is why unsaturated fats tend to be liquid at room

temperature, while saturated fats tend to be solid. Fatty acid chains with many double bonds

are calledpoly-unsaturatedfatty acids.

36 2.4. Organic compounds