The familiar term blood sugar is actually a reference to a specific chemical compound known to scientists as glucose. There are many types of sugars, but of these, glucose is the most common. It's found either on its own or incorporated into other, larger molecules. For instance, both table sugar and starch contain glucose. Glucose is an important source of energy for cells, and is the primary fuel source for the brain.
Chemical Characteristics
The glucose molecule occurs in nature either as a straight chain or as a ring structure--the ring is more common, particularly when glucose is combined with other molecules into larger compounds. The glucose ring consists of a backbone of five carbon atoms and one oxygen atom, forming a rough hexagon shape. This ring structure is called a "pyranose," explain Drs. Reginald Garrett and Charles Grisham. As such, glucose is sometimes called glucopyranose, to refer to its ring backbone. There are substituents, or arms, coming off the pyranose backbone--these are composed mostly of oxygen and hydrogen, arranged into groups called alcohols, each of which consists of one atom of oxygen and one atom of hydrogen. The many alcohol groups make glucose very soluble in water.
Optical Activity
Glucose is a so-called "chiral" molecule, meaning that it's asymmetric. This is important in chemistry, particularly in biochemistry, because for molecules to be active in the body, they must bind to the appropriate receptors. Glucose exists in two forms, which are mirror images of each other. Only one form occurs commonly in nature, but the mirror image form of glucose, though it contains all the same chemical components, can't bind to glucose receptors in the body, and therefore has no bioactivity. The active form of glucose shows right-handed optical activity, meaning that it rotates polarized light to the right, notes the "CRC Handbook of Chemistry and Physics." Only right-handed glucose can be absorbed by the body and provide cells with energy.
Polymerization
Many biomolecules can polymerize, meaning that they can combine with other similar molecules to produce short or long chains of repeating units. Glucose often combines with one other sugar unit, called fructose, to make table sugar, or sucrose. Even more common in nature, glucose can combine with hundreds of other glucose units to make long chains of glucose. Depending upon the orientation of the linkage between glucose units, these long chains have different chemical identities. One linkage orientation results in the production of starch, such as found in rice or potatoes, explain Drs. Mary Campbell and Shawn Farrell in their book, "Biochemistry." Other linkage orientations produce glycogen, which the liver uses to store glucose, and cellulose, which is indigestible plant fiber.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "CRC Handbook of Chemistry and Physics"; David Lide; 1974
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
