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The chemical formula for glucose is C 6 H 12 O 6 or H-(C=O)-(CHOH) 5 -H. Glucose is a sugar that is produced in plants during photosynthesis, and that circulates in the blood of people and other animals, being their main source of energy. Glucose is also known as dextrose, blood sugar, corn sugar, grape sugar, or by its IUPAC systematic name (2R , 3S , 4R , 5R ) -2,3,4,5,6 -Pentahydroxyhexanal.
glucose
The name glucose comes from the Greek term gleûkos which means “must or sweet wine”; The must is the first product of the pressing of the grapes that are later used to make wine. The ending “-ose” indicates that the molecule is a carbohydrate.
Because glucose is a molecule that has six carbon atoms, it is classified as hexose. It is an aldohexose. It is a type of monosaccharide or simple sugar. It can be structured in a linear or cyclical way, the latter being the most common way. In its linear form, it has a six-carbon backbone in which the C-1 carbon is the one that carries the aldehyde group, while the other five carbons each carry one hydroxyl group.
In glucose, hydrogen and hydroxyl (-OH) groups can rotate around carbon atoms, generating isomers. The D isomer, D-glucose, is the one found in nature participating in the processes of cellular respiration in plants and animals. The L isomer, L-glucose, is a synthetic compound, that is, it is not found in nature.
Pure glucose is a white or crystalline powder with a molecular mass of 180.16 grams per mole and a density of 1.54 grams per cubic centimeter. The melting point depends on the isomer. The melting point of α-D-glucose is 146°C while the melting point of β-D-glucose is 150°C.
Why do organisms use glucose instead of another carbohydrate? It could be because glucose is less likely to react with the amino groups of proteins. The reaction between carbohydrates and proteins, called glycation, is part of the natural aging process and leads to diseases, such as diabetes, that affect the functions of proteins. Rather, glucose can enzymatically combine with proteins and lipids through the process of glycosylation, forming active glycolipids and glycoproteins.
In the human body, glucose supplies energy of about 3.75 kilocalories per gram. It is metabolized producing carbon dioxide and water, releasing energy that is stored chemically as ATP (adenosine triphosphate). Although it is necessary for many functions, glucose is particularly important because it supplies almost all the energy needed by the human brain.
Glucose has the most stable cyclic form of all the aldohexoses because almost all of its hydroxyl (-OH) groups are in the equatorial position. The exception is the hydroxyl group on the anomeric carbon.
Glucose is soluble in water forming a colorless solution. It also dissolves in acetic acid, but is sparingly soluble in alcohol.
The glucose molecule was first isolated in 1747 by the German chemist Andreas Marggraf, who obtained it from raisins. Emil Fischer investigated the structure and properties of the molecule, winning the Nobel Prize in Chemistry in 1902 for his work. In the Fischer projection, glucose is spatially distributed in a specific pattern. The hydroxyl groups at carbons C-2, C-4, and C-5 are to the right of the carbon backbone, while the hydroxyl group at carbon C-3 is to the left.
Sources
- Robyt, John F. Essentials of Carbohydrate Chemistry . Springer Science & Business Media. 2012. ISBN:978-1-461-21622-3.
- Rosanoff, M. A. On Fischer’s Classification of Stereo-Isomers . Journal of the American Chemical Society. 28: 114–121. doi: 10.1021/ja01967a014
- Schenck, Fred W. Glucose and Glucose-Containing Syrups. Ullmann’s Encyclopedia of Industrial Chemistry. doi: 10.1002/14356007.a12_457.pub2
