Ribose and glucose are both monosaccharides, meaning they are sugars. Chemically, they're fairly similar. Both are carbohydrates, both are highly water soluble, and both consist of the elements carbon, hydrogen, and oxygen. While glucose is far more ubiquitous in nature and prevalent in food than ribose, cells can use both sugars to provide for energy needs.
Glucose Function
Glucose has two functions as a component of cellular material. It is primarily an energy molecule, and humans take it in, store it as necessary, and burn it in cells. Plants, similarly, burn glucose for energy. They also use it for structural material, however, and plant fibers are made up of long chains of glucose molecules linked together. These chains are called cellulose and are indigestible to humans, note Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Ribose Function
Although cells can metabolize and use ribose to provide for energy needs, it isn't as common in the diet as glucose. This is because it's not as ubiquitous in nature, showing up only in one very important place--as a structural component of the genetic material RNA. As Drs. Garrett and Grisham explain, RNA is similar to DNA, but most organisms don't rely upon it as a source of permanent genetic information--instead, RNA molecules are made as needed and broken down quickly.
Features
Both the raw materials--carbon, oxygen, and hydrogen--and the molecular structure of glucose and ribose are similar. Both are aldoses, meaning that the sugars contain an aldehyde functional group composed of a single carbon, hydrogen, and oxygen. Glucose is a hexose, or six-carbon sugar, while ribose is a pentose, or five-carbon sugar. Both have many alcohol, or OH, groups, which makes them both very water soluble, note Mary Campbell, Ph.D., and Shawn Farrell, Ph.D., in their book "Biochemistry."
Glucose Metabolism
The pathway through which the human body processes the majority of glucose starts with a series of reactions called glycolysis, which result in the production of two molecules of pyruvate, note Drs. Campbell and Farrell. The pyruvate then passes into the Kreb's cycle, through which it's converted into the waste products carbon dioxide and water. Ultimately, chemical combustion of glucose leads to the production of a significant amount of energy that can be used to run cellular processes.
Ribose Metabolism
Unlike glucose, ribose doesn't have a metabolic pathway custom-tailored to extract energy from the molecule. Instead, a series of enzyme-catalyzed reactions convert ribose into intermediates, or chemical waypoints, in glycolysis. From here, the molecules can finish out the process of glycolysis, eventually becoming pyruvate, and enter the Kreb's cycle. While each glucose produces two pyruvate molecules, each ribose produces only one, and since the mechanisms are different, ribose yields less than half the energy per sugar that glucose does, note Drs. Campbell and Farrell.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
