Carbohydrates: Chemistry & Identification
Today, scientists use a combination of biology and chemistry for their understanding of life and life processes.
Thus, an understanding of some chemistry of living things is necessary. Carbohydrates make up a large group
of chemical compounds found in cells. Carbohydrates are an energy source or are used in making cell
structures. There are three different groups of carbohydrates. They are called monosaccharides, disaccharides,
and polysaccharides. “Saccharide” means sugar.
Identifying Carbohydrates Using Models
Group 1. Monosaccharides- Monomers of Carbohydrates
A single molecule of sugar is called a monosaccharide. The prefix “mono-” means one. Sugars (saccharides) are
ring shaped (hexagon or pentagon). Look at the three examples of monosaccharides below (in figure 6-1) and
answer the following questions:
1. What three chemical elements are present in the three monosaccharides shown? ____ ____ _____
2. Add subscripts to the following to indicate the proper molecular formula. Fill in the blanks by counting the
total number of carbon, hydrogen, and oxygen atoms in each molecule.
glucose C ___ H ___ O ___
fructose C ___ H ___ O ___
galactose C ___ H ___ O ___
Group 2. Disaccharides- Polymers of Carbohydrates
Two monosaccharide sugar molecules can join chemically to form a larger carbohydrate molecule called a
double sugar, or disaccharide. The prefix “di-” means two. By chemically joining a glucose molecule with a
fructose molecule, a double sugar called sucrose (common table sugar) is produced. The process of joining
smaller molecules together to former larger molecules is called polymerization. When polymerization occurs
between organic molecules, water is released.
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Locate the models of fructose and glucose. How can you tell them apart? (Discuss)
3. Draw a simple version of the sugar molecules (just the rings, none of the bonds coming off the rings).
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In order to join the molecules, remove an –O-H end from one molecule, and an –H end from the
other
Join the two molecules together at the sights where your removed the –O-H and -H
4. Add the bonds to your picture in question 3 to show your monosaccharides now joined as a dissacharide.
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Join the –O-H and –H that your previously removed from the monosaccharides to each other
5. What molecule did you form by joining the –O-H and the –H? ________ or _____________
Group 3. Polysaccharides- Polymers of Carbohydrates with more than 2 rings
Just as double sugars were formed from two single sugar molecules, polysaccharides are formed when many
single sugars are joined chemically. The prefix “poly-” means many. Starch, glycogen, and cellulose are the
three most common polysaccharides in biology. They consist of long chains of glucose molecules joined
together.
6. Draw a simple version (rings only, none of the bonds coming of the ring) of a starch molecule made from 6
glucose molecules.
7. How many water molecules do you think would be made in making the starch molecule in number 6? ____
Analysis
1. “Mono-” means one, “di-” means two, and “poly-” means many. What are these terms used in describing the
three types of sugars?
2. Which types of sugars are considered polymers of carbohydrates?