Video Transcript
Which of the following best
explains why carbohydrates and proteins are classified as polymers? (A) Because there are many copies
of carbohydrates and proteins within the human body; poly- means many. (B) Because they are made up of
many different large units, monomers. (C) Because they are made up of
many similar small units, monomers. Or (D) because they are joined up
to other biological molecules.
As is correctly stated in answer
option (A), the prefix poly- means many. However, rather than meaning many
molecules, polymer actually describes a single large molecule composed of many
smaller units bonded together. Let’s consider the examples given
in the question. Starch is a common example of a
carbohydrate polymer. Starch is just a long chain of
glucose molecules joined together with glycosidic bonds. The small units, in this case
glucose, which make up the polymer are known as monomers.
Hemoglobin is an example of a
protein. Proteins tend to be more complex
molecules than carbohydrates, often being composed of multiple subunits. Hemoglobin consists of four
subunits. Each subunit is composed of amino
acids joined together with peptide bonds. In this case, each subunit is a
polymer and the amino acids are the monomers. It’s important to note that we
define monomers as similar small units because they are not always identical within
the same polymer. For example, a protein might
contain arginine, lysine, valine, and histidine, which are all amino acids but which
have slightly different chemical structures, represented by different colors on this
diagram.
We have therefore determined that
the correct answer is (C). The best explanation for why
carbohydrates and proteins are classified as polymers is because they are made up of
many similar small units, monomers.
