Glucose

Glucose, a simple monosaccharide sugar, is one of the most important carbohydrates and is used as a source of energy in animals and plants. Glucose is one of the main products of photosynthesis and starts respiration. The natural form (D-glucose) is also referred to as dextrose, especially in the food industry.

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Glucose (C6H12O6, molecular weight 180.18) is a hexose—a monosaccharide containing six carbon atoms. Glucose is an aldehyde (contains a -CHO group). Five of the carbons plus an oxygen atom form a loop called a "pyranose ring", the most stable form for six-carbon aldoses. In this ring, each carbon is linked to hydroxyl and hydrogen side groups with the exception of the fifth atom, which links to a 6th carbon atom outside the ring, forming a CH2OH group. This ring structure exists in equilibrium with a more reactive acyclic form, which makes up 0.0026% at pH 7.

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Glucose is a ubiquitous fuel in biology. We can speculate on the reasons why glucose, and not another monosaccharide such as fructose, is so widely used. Glucose can form from formaldehyde under abiotic conditions, so it may well have been available to primitive biochemical systems. Probably more important to advanced life is the low tendency of glucose, by comparison to other hexose sugars, to nonspecifically react with the amino groups of proteins. This reaction (glycosylation) reduces or destroys the function of many enzymes. The low rate of glycosylation is due to glucose's preference for the less reactive cyclic isomer. Nevertheless, many of the long-term complications of diabetes (e.g., blindness, kidney failure, and peripheral neuropathy) are probably due to the glycosylation of proteins.

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In respiration, through a series of enzyme-catalysed reactions, glucose is oxidized to eventually form carbon dioxide and water, yielding energy, mostly in the form of ATP. It is also broken down from polysaccharides before use.

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Chemically joined together, glucose and fructose form sucrose. Starch, cellulose, and glycogen are common glucose polymers (polysaccharides).

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The older name dextrose arose because a solution of D-glucose rotates polarised light towards the right. In the same vein D-fructose was called "levulose" because a solution of levulose rotates polarised light to the left.

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Monosaccharide: Monosaccharides are carbohydrates in the form of simple sugars....

Sugar: :This article deals with sugar as food and as an important, widely traded commodity. The word also has other uses; see sugar (disambiguation)....

Carbohydrate: Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. Relatively complex carbohydrates are known as polysaccharides. Carbohydrates are naturally produced by plants and animals. ...