Video Transcript
Glucose is a hexose sugar that
takes the form of two isomers. The basic structures of these
isomers are outlined in the provided diagram. Which of the two isomers shows the
structure of 𝛼-glucose? (A) Isomer X, (B) isomer Y, or (C)
neither of them.
This question shows us two diagrams
of different isomers of glucose, then asks us to choose the diagram that represents
𝛼-glucose. An isomer is a molecule that has
the same chemical formula but different structure. Both of the molecular diagrams have
a chemical formula of C6H12O6. This means that there are six atoms
of carbon, 12 atoms of hydrogen, and six atoms of oxygen in each glucose
molecule. Each of the vertices in the
hexagon, except for the one occupied by an atom of oxygen, actually represents an
atom of carbon. So what is the structural
difference?
We can see here, where the first
carbon atom is located, that the position of the hydrogen atom and the hydroxyl
group are switched. This difference affects how the
different isomers of glucose form chemical bonds. Because of the arrangement of the
atoms in isomer X, it will tend to make curved, branched chains when it
polymerizes.
One common polymer made from this
isomer of glucose is starch, a material used for glucose storage in plants. Starch is a polymer of
𝛼-glucose. Because of the arrangement of the
atoms in isomer Y, it will tend to make long, unbranched chains when it
polymerizes. One common polymer made from this
isomer of glucose is cellulose, the material that strengthens the cell walls of
plants. Cellulose is a polymer of
𝛽-glucose.
Using this information, we can
choose the correct answer to the question. The isomer that shows the structure
of 𝛼-glucose is isomer X.
