Back | Return to Index | Forward
Glucose | Return to Home | Wheat
Captain's Cards
I guess I'm not cut out for the simple life. I didn't know that being part of a monosaccharide like glucose would be so routine. I think it's time to move on. I've heard some of the other glucose molecules talking about joining forces and becoming a long chain called a polysaccharide. I was a little nervous about this because I didn't even know what a polysaccharide was, but some of the other glucans informed me that we're going to become a starch. Why didn't they just say that in the first place? Well, now I'm pretty excited. I'm going to be a complex carbohydrate -- sounds more intriguing than a simple sugar!
The products of photosynthesis are assembled in the wheat plant to make glucose. Glucose (C6H12O6) is a monosaccharide or single sugar. The plant uses glucose as short-term energy storage. Like all other organisms, however, the wheat plant must store energy "for a rainy day" (or for a dry day in this case!) Some of its glucose, therefore, is converted into a polysaccharide called starch, allowing the plant to store most of the energy collected in photosynthesis in the chemical bonds between the sugars. When the plant or the animal who ate the plant needs energy, the bonds holding the glucose molecules together are broken, and energy is released. Starch is a better way to store energy than glucose because it has more bonds to hold potential energy and it can be stored in large amounts without disturbing the rest of the plant.
The plant converts the monosaccharide (one sugar) to a polysacccharide (many sugars) by a process called starch synthesis. Basically, many glucose molecules link up and form a long chain which has new properties and is known as starch or amylose. The actual bonds between glucose molecules are formed through dehydration synthesis. This process literally means assembling by removing water. An atom of hydrogen (H) is removed from one of the glucans, and a hydroxyl group (OH) is removed from another. (The H and OH that were removed will react to form water,H2O.) The removal of the H and OH leaves free reactive sites which join together, linking the two glucans by a glycosidic bond to form a disaccharide (two sugars). Additional sugars are added to the chain by the same process to form the polysaccharide starch.
There are actually two types of starch molecules: amylose and amylopectin. These two types of starch molecules are both made up of glucose molecules. The only difference between the two is the arrangement of the molecules. Amylose is essentially linear while amylopectin has many branches like a tree. For sake of simplicity, we will follow Captain Carbon through
amylose. Amylose is made up of between 1000 and 4400 glucans. That is a long chain of
glucose molecules! These chains are stored in the endosperm of the wheat kernel. Plants can
package starch into small granules which can be stored in large amounts without upsetting the
balance of liquids going in and out of the cell. Starch, therefore, is able to store surplus
energy in a readily accessible form without disturbing the rest of the cell and plant, making it
an ideal means of long-term energy storage.