You may have heard that sugar is bad for you. Well, that’s not exactly true. When people say sugar is bad for you, they usually refer to sugars added to foods and drinks, like table sugar (sucrose). While it is true that consuming high levels of sugars too often can lead to negative health effects, sugars are essential to the survival of living organisms.
Carbohydrates are the most common type of organic compound. A carbohydrate is an organic compound such as sugar or starch and is used to store energy. Like most organic compounds, carbohydrates are built of small, repeating units that form bonds with each other to make a larger molecule. In the case of carbohydrates, the small repeating units are called monosaccharides. Carbohydrates contain only carbon, hydrogen, and oxygen.
A monosaccharide, the monomer of carbohydrates, is a simple sugar such as fructose or glucose. Fructose is mostly found in fruits, whereas glucose generally results from the digestion of other carbohydrates. Glucose (C6H12O6) is used for energy by the cells of most organisms and is a product of photosynthesis.
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Another monosaccharide, fructose, has the same chemical formula as glucose, but the atoms are arranged differently. Molecules with the same chemical formula but with atoms in a different arrangement are called isomers. Compare the glucose and fructose molecules in the Figure below. Can you identify their differences? The only differences are the positions of some of the atoms. These differences affect the properties of the two monosaccharides.
If two monosaccharides bond together, they form a carbohydrate called a disaccharide. An example of a disaccharide is sucrose (table sugar), which consists of the monosaccharides glucose and fructose (Figure above). Monosaccharides and disaccharides are also called simple sugars. They provide the major source of energy to living cells.
A polysaccharide is a complex carbohydrate that forms when simple sugars bind together in a chain. Polysaccharides may contain just a few simple sugars or thousands of them. Complex carbohydrates have two main functions: storing energy and forming structures of living things. Some examples of complex carbohydrates and their functions are shown in the Table below. Which type of complex carbohydrate does your own body use to store energy?
| Name | Function | Example |
|---|---|---|
| Starch | Used by plants to store energy. |
A potato stores starch in underground tubers. |
| Glycogen | Used by animals to store energy. |
A human stores glycogen in liver cells. |
| Cellulose | Used by plants to form rigid walls around cells. |
Plants use cellulose for their cell walls. |
| Chitin | Used by some animals to form an external skeleton. |
A grasshopper uses chitin for its exoskeleton. |
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For years there’s been a buzz, both positive and negative, about generating ethanol fuel from corn. Is this a good idea? Is it necessary? These questions need to be discussed. However, the Bay Area of California is rapidly becoming a world center for the next generation of green fuel alternatives. The Joint BioEnergy Institute is developing methods to isolate biofuels from the sugars in cellulose.
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