Video Transcript
What type of reaction forms a
triglyceride from a glycerol molecule and three fatty acids? (A) Hydrolysis, (B)
condensation/dehydration, (C) oxidation, (D) reduction, or (E) substitution.
This question is asking about the
biological molecules lipids and one group of them in particular called
triglycerides. Let’s review the key facts about
these lipids and how they are formed so we can come up with the correct answer to
the question.
Triglycerides, like all lipids, are
made up of carbon, hydrogen, and oxygen atoms, with far more hydrogen and carbon
than oxygen. The tri- part of their name refers
to their three fatty acid chains. The “glyceride” part refers to the
glycerol molecule, which is their other component. Glycerol, as its name suggests, is
an alcohol with three carbons. A fatty acid is a molecule made up
of a carboxyl group attached to a hydrocarbon tail, which is a chain of carbon atoms
two to 27 carbons with hydrogen atoms attached. When three fatty acids bind to one
glycerol molecule, they form a triglyceride.
Let’s now look at this reaction so
we can answer the question. If you look at the glycerol
molecule in the diagram, you will see that each of the three carbon atoms is bound
to a hydroxyl group and either one or two hydrogens. Also, as mentioned earlier, the
fatty acids have a carboxyl group at one end. The carboxyl group consists of one
carbon atom, an oxygen, which has formed a double bond with the carbon, and a
hydroxyl group.
Covalent bonds, called ester bonds,
will form between the carboxyl group of each fatty acid and the hydroxyl groups on
the glycerol, as shown here. You may also notice on the diagram
that a water molecule is released when each ester bond forms. When a reaction occurs resulting in
two molecules combining to form a single molecule, with the loss of a small
molecule, such as water, it is known as a condensation reaction. If water is lost, it can also be
called dehydration synthesis.
Now that we have reviewed how fatty
acids combine with glycerol to form triglycerides, we can return to the
question. We now know that the correct answer
is option (B). A triglyceride forms from a
glycerol and three fatty acids as a result of a condensation reaction.
