Difference between revisions of "Glucose" - New World Encyclopedia
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==The function of glucose== | ==The function of glucose== | ||
| − | We can speculate on the reasons why glucose, and not another monosaccharide such as [[fructose]] (Fru) , is so widely used in evolution/the ecosystem/metabolism. 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 non-specifically react with the [[amino]] groups of [[protein]]s | + | We can speculate on the reasons why glucose, and not another monosaccharide such as [[fructose]] (Fru) , is so widely used in evolution/the ecosystem/metabolism. 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 non-specifically react with the [[amino]] groups of [[protein]]s (their preference for a ring form makes them less reactive). |
===As an energy source=== | ===As an energy source=== | ||
| − | + | Glucose is a ubiquitous fuel in [[biology]]. Carbohydrates are the human body's key source of energy, providing 4 [[kilocalorie]]s (17 [[kilojoule]]s) of [[food energy]] per [[gram]]. The breakdown of carbohydrates, whether stored as [[glycogen]] or taken in through the diet, yields mono- and disaccharides, many of which are glucose molecules. In the [[anaerobic]] process of [[glycolysis]] and later in the reactions of the [[Citric acid cycle]] (TCAC), glucose is [[oxidize|oxidized]] to form [[carbon dioxide|CO<sub>2</sub>]] and [[water]], yielding energy, mostly in the form of [[adenosine triphosphate|ATP]]. | |
| − | |||
| − | Glucose is a ubiquitous fuel in [[biology]]. Carbohydrates are the human body's key source of energy, providing 4 [[kilocalorie]]s (17 [[kilojoule]]s) of [[food energy]] per [[gram]]. | ||
===As a precursor to other biological molecules=== | ===As a precursor to other biological molecules=== | ||
| − | Glucose is critical in the production of [[protein]]s and in [[lipid]] metabolism. | + | In plants and most animals, glucose is a precursor for the production of [[vitamin C]] (ascorbic acid). Glucose is also critical in the production of [[protein]]s and in [[lipid]] metabolism. [[Glycation]] and [[glycosylation]] are two important types of reactions undergone by glucose. |
| − | Glucose is used as a precursor for the synthesis of several important | + | Glucose is used as a precursor for the synthesis of several important carbohydrates. [[Starch]], [[cellulose]], and [[glycogen]] are common glucose [[polymer]]s ([[polysaccharide]]s). Glycogen is the body's auxiliary energy source, tapped and converted back into glucose when there is need for energy. |
| + | [[Lactose]], the predominant sugar in milk, is a glucose-[[galactose]] disaccharide. In [[sucrose]], another important [[disaccharide]], glucose is joined to fructose. | ||
==The body's regulation of glucose== | ==The body's regulation of glucose== | ||
| − | The insulin | + | The body regulates the concentration of glucose in the blood through the action of the hormones [[insulin]], which directs the flow of glucose into cells, and [[glucagon[[ and [[epinephrine]], which retrieve glucose from its storage form as glycogen in liver and muscle tissue. Low blood sugar (hypoglycemia). Elevated blood sugar (hyperglycemia) in [[diabetes]]. |
==Commercial production== | ==Commercial production== | ||
Revision as of 01:18, 31 July 2006
| Glucose | |
|---|---|
| |
| Chemical name | 6-(hydroxymethyl)oxane-2,3,4,5-tetrol |
| Synonym for D-glucose | dextrose |
| Varieties of D-glucose | α-D-glucose; β-D-glucose |
| Abbreviations | Glc |
| Chemical formula | C6H12O6 |
| Molecular mass | 180.16 g mol−1 |
| Melting point | α-D-glucose: 146°C β-D-glucose: 150°C |
| Density | 1.54 g cm-3 |
| CAS number | 50-99-7 (D-glucose) |
| CAS number | 921-60-8 (L-glucose) |
| SMILES | C(C1C(C(C(C(O1)O)O)O)O)O |
Glucose (Glc) is a monosaccharide (or simple sugar) with the chemical formula C6H12O6. It is the major free sugar circulating in the blood of higher animals, and the preferred fuel of the brain and nervous system, as well as red blood cells.
Glucose is of central importance in the metabolism of all life forms, as a universal substrate for the production of cellular energy in the form of ATP. It is both one of the main products of photosynthesis, the process by which plants, algae, some bacteria, and some protists convert energy from sunlight into chemical energy to be used by the cell, and a major starting point for cellular respiration, the process by which the chemical bonds of energy-rich molecules such as glucose are converted into energy usable for life processes.
All major dietary carbohydrates contain glucose, either as their only building block, as in starch and glycogen, or in combination with another monosaccharide, as in sucrose (“table sugar”) and lactose, the primary sugar found in milk.
The natural form of glucose (D-glucose) is also referred to as dextrose, especially in the food industry.
The structure of glucose
Sugars are classified according to the number of carbon atoms and the type of functional group (either an aldehyde or ketone group) they contain. Glucose is referred to as an aldohexose because it contains six carbon atoms (i.e., it is a hexose sugar) and an aldehyde group (-CHO).
The glucose molecule can exist in an open-chain (acyclic) and a ring (cyclic) form. In solution and at neutral pH, the cyclic form is predominant at equilibrium. When glucose exists in cyclic form, the functional group is not free, making the molecule less reactive.
Isomers
Glucose has 4 optic centers which means that in theory glucose can have (4²-1) = 15 optical stereoisomers. Only 7 of these are found in living organisms, and of these galactose (Gal) and mannose (Man) are the most important. These eight isomers (including glucose itself) are all diastereoisomers in relation to each other and all belong to the D-series.
Natural sources of glucose
- Glucose is one of the products of photosynthesis in plants and some prokaryotes.
- In animals and fungi, glucose is the result of the breakdown of glycogen, a process known as glycogenolysis. In plants - the breakdown substrate is starch.
- In animals, glucose is synthesized in the liver and kidneys from non-carbohydrate intermediates, such as pyruvate and glycerol, by a process known as gluconeogenesis.
The function of glucose
We can speculate on the reasons why glucose, and not another monosaccharide such as fructose (Fru) , is so widely used in evolution/the ecosystem/metabolism. 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 non-specifically react with the amino groups of proteins (their preference for a ring form makes them less reactive).
As an energy source
Glucose is a ubiquitous fuel in biology. Carbohydrates are the human body's key source of energy, providing 4 kilocalories (17 kilojoules) of food energy per gram. The breakdown of carbohydrates, whether stored as glycogen or taken in through the diet, yields mono- and disaccharides, many of which are glucose molecules. In the anaerobic process of glycolysis and later in the reactions of the Citric acid cycle (TCAC), glucose is oxidized to form CO2 and water, yielding energy, mostly in the form of ATP.
As a precursor to other biological molecules
In plants and most animals, glucose is a precursor for the production of vitamin C (ascorbic acid). Glucose is also critical in the production of proteins and in lipid metabolism. Glycation and glycosylation are two important types of reactions undergone by glucose.
Glucose is used as a precursor for the synthesis of several important carbohydrates. Starch, cellulose, and glycogen are common glucose polymers (polysaccharides). Glycogen is the body's auxiliary energy source, tapped and converted back into glucose when there is need for energy. Lactose, the predominant sugar in milk, is a glucose-galactose disaccharide. In sucrose, another important disaccharide, glucose is joined to fructose.
The body's regulation of glucose
The body regulates the concentration of glucose in the blood through the action of the hormones insulin, which directs the flow of glucose into cells, and [[glucagon[[ and epinephrine, which retrieve glucose from its storage form as glycogen in liver and muscle tissue. Low blood sugar (hypoglycemia). Elevated blood sugar (hyperglycemia) in diabetes.
Commercial production
Glucose is produced commercially through the breakdown of starch in an enzyme-catalyzed process called hydrolysis (a chemical reaction in which a molecule is split into two parts through the addition of water). The enzymatic process has two stages:
- Over the course of 1-2 hours near 100 °C, these enzymes break the starch into smaller carbohydrates containing on average 5-10 glucose units each. Some variations on this process briefly heat the starch mixture to 130 °C or hotter one or more times. This heat treatment improves the solubility of starch in water, but deactivates the enzyme, so that fresh enzyme must be added to the mixture after each heating.
- In the second step, known as saccharification, the partially hydrolyzed starch is completely hydrolyzed to glucose using the glucoamylase enzyme from the fungus Aspergillus niger. Typical reaction conditions are pH 4.0–4.5, 60 °C, and a carbohydrate concentration of 30–35% by weight. Under these conditions, starch can be converted to glucose at 96% yield after 1–4 days. Still higher yields can be obtained using more dilute solutions, but this approach requires larger reactors and the processing of a greater volume of water, which is not generally economical.
The resulting glucose solution is then purified by filtration and concentrated in a multiple-effect evaporator. Solid D-glucose is then produced by repeated crystallizations.
Many crops can be used as sources of starch in the commerical production of glucose, including maize, rice, wheat, potato, cassava, arrowroot, and sago. In the United States, cornstarch (from maize) is used almost exclusively.
External links
- EINECS number 200-075-1 (D-glucose)
- EINECS number 213-068-3 (L-glucose)
- CID 5793 from PubChem (D-glucose)
- CID 206 from PubChem (L-glucose)
- More on the chemistry and function of glucose in biology at EvoWiki
- Computational Chemistry Wiki
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