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Glucose

 

GlucoseD-glucose or dextrose or grape sugar is the dextro-isomer of glucose (C6H12O6). The molecule is the mirror-image of L-glucose. D-glucose is a simple sugar (monosaccharide) and an important carbohydrate in biology. Cells use it as a source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and starts cellular respiration. Starch and cellulose are polymers derived from the dehydration of glucose. The name “glucose” comes from the Greek word glukus, meaning “sweet.” The suffix “-ose” denotes a sugar.

Glucose exists in several different structures, but all of these structures can be divided into two families of mirror-images (stereoisomers). Only one set of these isomers exists in nature, those derived from the “right-handed form” of glucose, denoted D-glucose. D-glucose is often referred to as dextrose. The term dextrose is derived from dextrorotatory glucose. Solutions of dextrose rotate polarized light to the right (in Latin: dexter = “right” ).

Structure

Although it is called a “simple sugar” (meaning that it is a monosaccharide), glucose is a complicated molecule because it adopts several different structures. These structures are usually discussed in the context of the acyclic isomer, which exists in only minor amounts in solution.

Glucose is derived from hexanal, a chain of six carbon atoms terminating with an aldehyde group. The other five carbon atoms each bear alcohol groups. Glucose is called an aldohexose. In solution, glucose mainly exists as the six-membered ring containing a hemiacetal group, which arises from the reaction of the hydroxy group at C-5 and the aldehyde at C-1. Containing five carbon atoms and one oxygen atom, this ring is a derivative of pyran. This cyclic form of glucose is called a glucopyranose, of which two isomers exist.

Function

Glucose metabolism and various forms of it in the process.

Glucose-containing compounds and isomeric forms are digested and taken up by the body in the intestines, including starch, glycogen, disaccharides and monosaccharides.

Glucose is stored in mainly the liver and muscles as glycogen.

-It is distributed and utilized in tissues as free glucose.

Scientists can speculate on the reasons why glucose, and not another monosaccharide such as[fructose (Fru), is so widely used in organisms. One reason might be that glucose has a lower tendency, relative to other hexose sugars, to react non-specifically with the amino groups of proteins. This reaction (glycation) reduces or destroys the function of many enzymes. The low rate of glycation is due to glucose’s preference for the less reactive cyclic isomer. Nevertheless, many of the long-term complications of diabetes (e.g., blindness, renal failure, and peripheral neuropathy) are probably due to the glycation of proteins or lipids.[6] In contrast, enzyme-regulated addition of glucose to proteins by glycosylation is often essential to their function.

As an energy source

Glucose is a ubiquitous fuel in biology. It is used as an energy source in most organisms, from bacteria to humans. Use of glucose may be by either aerobic respiration, anaerobic respiration, or fermentation. Carbohydrates are the human body’s key source of energy, through aerobic respiration, providing approximately 3.75 kilocalories (16 kilojoules) of food energy per gram. Breakdown of carbohydrates (e.g. starch) yields mono- and disaccharides, most of which is glucose. Through glycolysis and later in the reactions of the citric acid cycle (TCAC), glucose is oxidized to eventually form CO2 and water, yielding energy sources, mostly in the form of ATP. The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood. A high fasting blood sugar level is an indication of prediabetic and diabetic conditions.
Glucose is a primary source of energy for the brain, and hence its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g., self-control, effortful decision-making) are impaired.

Glucose in glycolysis

Compound C00031 at KEGG Pathway Database. Enzyme 2.7.1.1 at KEGG Pathway Database. Compound C00668 at KEGG Pathway Database. Reaction R01786 at KEGG Pathway Database.

Use of glucose as an energy source in cells is via aerobic or anaerobic respiration. Both of these start with the early steps of the glycolysis metabolic pathway. The first step of this is the phosphorylation of glucose by hexokinase to prepare it for later breakdown to provide energy.

The major reason for the immediate phosphorylation of glucose by a hexokinase is to prevent diffusion out of the cell. The phosphorylation adds a charged phosphate group so the glucose 6-phosphate cannot easily cross the cell membrane. Irreversible first steps of a metabolic pathway are common for regulatory purposes.

As a precursor

Glucose is critical in the production of proteins and in lipid metabolism. In plants and most animals, it is also a precursor for vitamin C (ascorbic acid) production. It is modified for use in these processes by the glycolysis pathway.

Glucose is used as a precursor for the synthesis of several important substances. Starch, cellulose, and glycogen (“animal starch”) are common glucose polymers (polysaccharides). Lactose, the predominant sugar in milk, is a glucose-galactose disaccharide. In sucrose, another important disaccharide, glucose is joined to fructose. These synthesis processes also rely on the phosphorylation of glucose through the first step of glycolysis.

Chinese Slimming Tea

Glucose is one the main ingredients in Natural Line’s Chinese Slimming Tea and helps achieve general health and get rid of extra weight.

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