Video Transcript
Which polymers are formed when
monosaccharides, e.g., glucose or fructose, join together via glycosidic bonds? Option (A) proteins, option (B)
carbohydrates, option (C) lipids, or option (D) glycerols.
This question is asking about the
formation of polymers. To answer this question, we need to
go over the key facts about the three main types of biological macromolecules and
how they are formed.
Let us first examine the concept of
monomers versus polymers. A monomer is a single subunit:
mono- meaning one and -mer meaning part. Polymers are made up of many
monomers bonded together. Poly- means many. So proteins are made from
polypeptides, which are polymers made up of many amino acids, the monomers, joined
together.
Complex carbohydrates, such as
starch, are polymers called polysaccharides. These are made up of many monomers
called monosaccharides joined together. The main monosaccharides you need
to know are glucose, fructose, and galactose. Note the suffix -ose for
sugars.
Lipids are not polymers, as they
are not made up of repeating units. The type of lipid shown here is a
triglyceride, which is a common one and made up of glycerol and fatty acids.
The single units are covalently
bonded together to make up the macromolecules. Each type of macromolecule will use
a different kind of bond. In proteins, it’s a peptide
bond. In carbohydrates, it’s a glycosidic
bond. And in lipids, it’s commonly an
ester bond.
Now that we have reviewed these key
facts, let’s narrow down our answer options. The question is asking, which
polymers are formed when monosaccharides, e.g., glucose or fructose, join together
via glycosidic bonds? The question asks us about
polymers, so we know it is referring to macromolecules that are made up of many
repeating units joined together. This therefore rules out lipids, as
lipids are not polymers. And it also rules out glycerols, as
glycerols are subunits of lipids.
We are left with the two polymers
proteins and carbohydrates. The question asks us about which
polymer is made up of monosaccharides, such as glucose or fructose. Saccharide means sugar, so the
polymer group the question asks about must be carbohydrates, which are made up of
monosaccharides bonded together by glycosidic bonds. Glucose and fructose are
monosaccharides. And when monosaccharides bond
together to form a polysaccharide, they use glycosidic bonds. Therefore, the correct answer is
(B), carbohydrates.
