Video Transcript
Monomers combine with each other
using bonds to form larger molecules known as polymers. Which of the following statements
shows a monomer that is correctly matched with its polymer? (A) An amino acid is a monomer of
proteins. (B) Glycerol is a monomer of fatty
acids. (C) Glucose is a monomer of
monosaccharides. Or (D) DNA is a monomer of nucleic
acids.
This question asks us to identify
which of the answer choices correctly pairs monomers with their polymers. These words can be broken down to
give us clues for what they mean. Here, the prefix poly- means many,
and -mer means unit. For the word “monomer,” we have
already seen that -mer means unit; well mono- means one. We can combine this information to
learn that polymers consist of single, repeating subunits that are called
monomers.
To answer this question correctly,
we should first review the key facts about the four biological macromolecule groups:
carbohydrates, nucleic acids, lipids, and proteins. Let’s look at these in turn to help
us narrow down the answer options.
Carbohydrates are built up of the
individual units called monosaccharides. The word “saccharide” means sugar,
so a monosaccharide is a single sugar unit. Glucose, fructose, and galactose
are all examples of monosaccharides. These monosaccharides can then be
joined together by glycosidic bonds to form polysaccharides, such as the storage
carbohydrates glycogen and starch. Both of these are composed of many
glucose molecules joined together. Therefore, we can rule out the
option (C) as glucose is a monosaccharide and is therefore also a monomer.
Now, let’s look at nucleic
acids. DNA is a type of nucleic acid found
in the nucleus of our cells. It is made up of repeating
monomers, called nucleotides. These nucleotides are held together
by phosphodiester bonds. DNA stores information that
contains instructions for making all of the proteins in the body. We can therefore also rule out
option (D) as DNA is a nucleic acid.
The next biological macromolecules
in our list are lipids. These include the phospholipids,
found in cell membranes, and triglycerides, used for energy stores. They are not considered polymers
since they do not contain repeating, monomer subunits. Phospholipids, for example, are
made up of different types of molecules, two fatty acids, a phosphate group, and a
glycerol molecule, held together by ester bonds. Therefore, we can remove option (B)
from the possible answers as both glycerol and fatty acids are molecules that make
up lipids, and lipids are not polymers.
Finally, we come to proteins. Proteins are made up of one or more
polypeptide chains. A peptide is a short chain of amino
acids, so a polypeptide is a long chain of amino acids. The amino acids are held together
by peptide bonds.
We can now return to our
question. Seeming as proteins are made of one
or more polypeptide chains, and polypeptides are made up of amino acids, we now know
that the correct answer is (A). The statement that shows a monomer
that is correctly matched with its polymer is “An amino acid is a monomer of
proteins.”
