Glucose
Glucose, also known as dextrose, is a simple carbohydrate with the molecular formula C6H12O6, making it one of the smallest and most fundamental carbohydrates, classified as a monosaccharide. It is a crucial energy source for living organisms, including humans, and plays a significant role in human metabolism as the primary sugar found in the bloodstream. Discovered in the 18th century by Andreas Sigismund Marggraf, glucose was named after the Greek word "glycos," meaning sweet. This compound can be produced by plants during photosynthesis, where it serves various functions, including storage as starch and incorporation into proteins and cellulose.
Glucose is metabolized in the body through a complex series of biochemical reactions, beginning with glycolysis, which converts glucose into pyruvate. This pyruvate then enters the Krebs cycle, a metabolic pathway that generates energy-rich molecules essential for cellular functions. The energy released during glucose metabolism also forms adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH), which are vital for energy transfer within cells. Glucose is not only important for its nutritional value but also for its application in medical settings, where it can be administered as an intravenous dietary supplement for individuals unable to digest food normally.
On this Page
Subject Terms
Glucose
Glucose, also called dextrose, is a carbohydrate, an organic compound composed solely of carbon and water with a general molecular formula of Cn (H2O)n. Glucose is considered a simple carbohydrate because, with a chemical composition of C6H12O6, it is one of the smallest carbohydrates. Carbohydrates are also called saccharides or sugars. Glucose is a monosaccharide or simple sugar, the smallest unit of such molecules. Other monosaccharides include galactose, a sugar found in dairy products, and fructose, a sugar found in fruits and vegetables.
Glucose is an important source of food for most living organisms, including humans, because it provides cells with energy. Of the three dietary sugars, glucose is the most important in human metabolism.
Overview
In 1747, after isolating sucrose from sugar beets, German pharmacist and chemist Andreas Sigismund Marggraf became the first person to isolate glucose from raisins. The white powder that Marggraf purified was sweet, but not as sweet as table sugar (sucrose), and he later found that its melting point was about 302 degrees Fahrenheit. Nineteenth-century French chemist Jean-Baptiste André Dumas named Marggraf’s raisin sugar molecule “glucose” after the Greek word for “sweet,” glycos.
In the late nineteenth century, Emil Fischer determined the molecular composition and structure of glucose. He also discovered that glucose occurs in two main forms, or isomers, only one of which is found in nature. The naturally occurring isomer rotates plane-polarized light to the right. Fischer called this form “D-glucose” for its dextrorotatory characteristics, as opposed to L-glucose, which rotates plane-polarized light to the left. In 1902 Fischer won the Nobel Prize in Chemistry for his work with glucose and other sugars.
Glucose is found in plant sap and fruit juices. It occurs as one of the products of photosynthesis, the process by which plants make glucose and oxygen from light, water, and carbon dioxide. Plants have glucose in their sap and can store glucose molecules as starches, oils, or fats. Plants can also convert glucose into proteins for repair and growth or into cellulose, a component of a plant’s cell walls.
In humans, glucose can be found in the blood, where it is known as “blood glucose” or “blood sugar,” and is the body’s main source of energy. As such, it does not need to be digested and can be provided as an intravenous dietary supplement to patients whose normal process of digestion has been disrupted. When the body metabolizes, or oxidizes, glucose, it yields energy as well as water, carbon dioxide, and nitrogen compounds. Cells use the energy to work or to provide heat.
The body’s metabolism of glucose takes place via a set of complex biochemical reactions. Glycolysis, the first series of reactions, converts glucose or another monosaccharide to pyruvate. The resulting pyruvate is a key component of the Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle. This cycle is a major metabolic pathway in all aerobic organisms. It produces energy-rich phosphate compounds, a primary source of cellular energy.
Glycolysis also releases free energy that forms adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH), two high-energy compounds. ATP transfers chemical energy within cells for metabolism. NADH is used in cells to transfer electrons.
Bibliography
Augustine, Demetrius. Cellular Metabolism in Cell Biology. Delhi: Research World, 2012. Digital file.
Coffey, Rebecca. “20 Things You Didn’t Know about . . . Sugar.” Discover. Kalmbach, 30 Oct. 2009. Web. 24 Sept. 2013.
Hollman, Siegfried. Non-Glycolytic Pathways of Metabolism of Glucose. New York: Academic, 1964. Print.
Hull, Peter. Glucose Syrups: Technology and Applications. Chichester: Wiley, 2010. Print.
Nicolaou, K. C., and Tamsyn Montagnon. Molecules That Changed the World. Weinheim: Wiley, 2008. Print.
Preedy, Victor R., ed. Dietary Sugars: Chemistry, Analysis, Function and Effects. Cambridge: RSC, 2012. Print.
Salway, J. G. Metabolism at a Glance. 3rd ed. Malden: Blackwell, 2004. Print.
Johnson, Carter C., and Davis B. Williams, eds. Glucose Uptake: Regulation, Signaling Pathways and Health Implications. New York: Nova, 2013. Print.