Glucose is a carbohydrate, a chemical compound made of C, H, and O on 1 to 2 to 1 ratio. Specifically, glucose is a monosaccharide, which means that it consists of a single sugar ring. Because of the structure of this ring, there are two forms of glucose, called alpha and beta, with slightly different chemical properties.
Structure of Glucose
The glucose molecule has the chemical formula C6H12O6. It consists of a six-membered ring, made of five atoms of carbon and one atom of oxygen. The remaining hydrogens, oxygens, and carbon form arms off the central ring. The orientation of one particular arm -- which consists of an oxygen and a hydrogen atom -- determines whether a particular glucose molecule is alpha-glucose or beta-glucose. In the beta form, the arm points upward, while in the alpha form, the arm points downward.
Form Conversion
In solution, alpha- and beta-glucose can freely interconvert between forms. This process is called "mutarotation" in biochemistry. The beta form is slightly more stable than the alpha form, so in a solution of free glucose, there will be a bit more beta-glucose than alpha-glucose, but molecules routinely switch their orientations, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." This is true in the body as well -- free glucose in the digestive tract, blood, or cells, can convert between alpha and beta forms.
Form Locking
Glucose becomes locked into either the alpha or beta form when it chemically bonds to other molecules -- often other molecules of sugar -- to form larger molecules. For instance, when glucose bonds to the similar sugar fructose to form sucrose, or table sugar, glucose gets locked into the alpha position. All the glucose molecules bonded together to form amylose, or starch, are locked into the alpha position. Glucose molecules bonded together to form cellulose, or fiber, are locked into the beta position.
Use of Glucose
Because free glucose can mutarotate between alpha and beta forms, the body uses alpha- and beta-glucose in identical manners. Your cells can break down alpha- and beta-glucose to provide energy to fuel various cellular processes, explains Dr. Lauralee Sherwood in her book "Human Physiology." You can convert either alpha- or beta-glucose into fat, storing the energy for later use. Finally, you can synthesize glycogen, a molecule that stores glucose, from either alpha- or beta- glucose -- though the glucose molecules get locked into the alpha position as you synthesize the glycogen molecule.
Digestion
When you consume a source of digestible glucose, even if the molecules are locked into position, enzymes in your digestive tract break the glucose molecules apart. When you eat starch, you break the alpha-glucose molecules apart from one another, and they are then free to convert into beta-glucose. As such, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry," you can eat entirely alpha-glucose, and still end up with a mixture of alpha- and beta-glucose in the digestive tract and bloodstream.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
